07ba12fb2068f5051d594fe4dbb95b2dea482043
92 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 Christopher Haster
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07ba12fb20 |
Moved gstate struct definitions into lfs3_t
Despite programming in C for quite a while, I didn't expect this to work. But it turns out you _can_ typedef nested structs, you just need to put the typedef outside the struct. IMO this makes it a bit easier to understand what state is exclusive to the lfs3_t struct. We do use these typedefs internally, but only for pointers into the core lfs3_t. No code changes. |
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Christopher Haster
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4f22d8c591 |
scripts: dbgflags.py: Added support for flag aliases
Also tweaked related flag comments a bit.
---
This adds another internal flag modifier ('a') to dbgflags.py to
indicate a flag is an alias for multiple other flags.
These still show up in -l/--list and name searches:
$ ./scripts/dbgflags.py -l +ck
LFS3_CK_MKCONSISTENT 0x00000100 Make the filesystem consistent
LFS3_CK_LOOKAHEAD 0x00000200 Repopulate lookahead buffer
LFS3_CK_COMPACT 0x00000800 Compact metadata logs
LFS3_CK_CKMETA 0x00001000 Check metadata checksums
LFS3_CK_CKDATA 0x00002000 Check metadata + data checksums
LFS3_CK_CK 0x00003000 Alias for all check work
LFS3_CK_GC 0x00003b00 Alias for all gc work
But are hidden from value searches, as they would be redundant and the
specific low-level flags are probably more useful:
$ ./scripts/dbgflags.py +ck 0x00003000
LFS3_CK_CKMETA 0x00001000 Check metadata checksums
LFS3_CK_CKDATA 0x00002000 Check metadata + data checksums
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Christopher Haster
|
124afb3034 |
Adopted LFS3_*_CK and LFS3_*_GC aliases, replacing LFS3_GC_ALL
This extends the hopefully useful LFS3_GC_ALL flag alias to the other functions, without trying to figure out what the heck LFS3_M_ALL should mean semantically. Current definitions: // an alias for ck work *_CK 0x00003000 ---- ---- ---- ---- --11 ---- ---- ---- // an alias for all possible gc work *_GC 0x00003b00 ---- ---- ---- ---- ++11 11+1 ---- ---- *_MKCONSISTENT 0x00000100 ---- ---- ---- ---- ---- ---1 ---- ---- *_LOOKAHEAD 0x00000200 ---- ---- ---- ---- ---- --1- ---- ---- *_PREERASE+ 0x00000400 ---- ---- ---- ---- ---- -+-- ---- ---- *_COMPACT 0x00000800 ---- ---- ---- ---- ---- 1--- ---- ---- *_CKMETA 0x00001000 ---- ---- ---- ---- ---1 ---- ---- ---- *_CKDATA 0x00002000 ---- ---- ---- ---- --1- ---- ---- ---- *_REPAIRMETA+ 0x00004000 ---- ---- ---- ---- -+-- ---- ---- ---- *_REPAIRDATA+ 0x00008000 ---- ---- ---- ---- +--- ---- ---- ---- + Planned One weird artifact of this is that LFS3_GC_CK ~= LFS3_GC_CKDATA, but I'm not sure that's a bad thing? Note this is very much not true for info flags, LFS3_I_CK != LFS3_I_CKDATA. No code changes. |
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Christopher Haster
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d54fef8099 |
Reorganized traversal flags again
One nice thing about merging LOOKAHEAD + LOOKGBMAP, is now our core
traversal flags fit in a single byte. This is useful for organizing
things, especially so as the traversal flags seem to permeate into
basically every flag set.
The main change was to actually group these flags into a byte, which
helps readability and in theory could make some bulk accesses cheaper
(in practice I don't think we currently leverage this):
T_MODE 0x00000001 ---- ---- ---- ---- ---- ---- ---- ---1
T_RDONLY 0x00000000 ---- ---- ---- ---- ---- ---- ---- ----
T_RDWR 0x00000001 ---- ---- ---- ---- ---- ---- ---- ---1
T_MTREEONLY 0x00000002 ---- ---- ---- ---- ---- ---- ---- --1-
T_EXCL 0x00000008 ---- ---- ---- ---- ---- ---- ---- 1---
T_MKCONSISTENT 0x00000100 ---- ---- ---- ---- ---- ---1 ---- ----
T_LOOKAHEAD 0x00000200 ---- ---- ---- ---- ---- --1- ---- ----
T_PREERASE* 0x00000400 ---- ---- ---- ---- ---- -1-- ---- ----
T_COMPACT 0x00000800 ---- ---- ---- ---- ---- 1--- ---- ----
T_CKMETA 0x00001000 ---- ---- ---- ---- ---1 ---- ---- ----
T_CKDATA 0x00002000 ---- ---- ---- ---- --1- ---- ---- ----
T_REPAIRMETA* 0x00004000 ---- ---- ---- ---- -1-- ---- ---- ----
T_REPAIRDATA* 0x00008000 ---- ---- ---- ---- 1--- ---- ---- ----
t_EVICT* 0x00000010 ---- ---- ---- ---- ---- ---- ---1 ----
t_TYPE 0xf0000000 1111 ---- ---- ---- ---- ---- ---- ----
t_ZOMBIE 0x08000000 ---- 1--- ---- ---- ---- ---- ---- ----
t_CKPOINTED 0x04000000 ---- -1-- ---- ---- ---- ---- ---- ----
t_DIRTY 0x02000000 ---- --1- ---- ---- ---- ---- ---- ----
t_STALE 0x01000000 ---- ---1 ---- ---- ---- ---- ---- ----
t_BTYPE 0x00ff0000 ---- ---- 1111 1111 ---- ---- ---- ----
* Planned
This gives btype a full byte as well, which is a bit overkill, but can
be reduced in the future if we run into traversal flag pressure.
This also pushes some future planned flags (DEDUP, COMPR, etc) into
higher-order bits, but that's not the end of the world.
Code changes basically nothing:
code stack ctx
before: 35152 2136 660
after: 35152 (+0.0%) 2136 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38080 2136 776
gbmap after: 38076 (-0.0%) 2136 (+0.0%) 776 (+0.0%)
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Christopher Haster
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7a57b1e2bd |
Renamed LFS3_T_COMPACTMETA -> LFS3_T_COMPACT (and gc_compact_thresh)
This effectively reverts
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Christopher Haster
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ffc565508a |
alloc: Merged LOOKAHEAD+LOOKGBMAP -> single LOOKAHEAD flag
Our flag space is already really packed, and I'm not sure having these
as separate flags is meaningful or useful for users. They both indicate
to repopulate allocators, and most users probably won't care that there
are two subtly different allocators operating under the hood.
There's an argument that LOOKAHEAD not touching disk is a useful
distinction, but in practice you really only need LOOKAHEAD work when
mounted RDWR.
So, merged the behaviors of LOOKAHEAD + LOOKGBMAP such that
LFS3_*_LOOKAHEAD requests repopulation of all allocators based on
gc_lookahead_thresh and gc_lookgbmap_thresh.
In priority order (some notes below):
1. If max(lookahead, gbmap) < gc_lookahead_thresh => repop lookahead
2. If gbmap < gc_lookgbmap_thresh => repop gbmap
As a plus, this makes it easier to avoid LFS3_IFDEF_GBMAP mess.
---
It's interesting to note LFS3_*_LOOKAHEAD will still repopulate the
lookahead buffer when the gbmap is present, but only if this would gain
more knowledge than was is currently in the gbmap.
I considered disabling lookahead scans completely when we have a gbmap,
but repopulating the lookahead buffer is still useful if the gbmap is at
risk of exhaustion. This is what gc_lookahead_thresh is for anyways, and
users can set gc_lookahead_thresh=0 if they want to disable this
behavior.
Relatedly, lookahead scans are actually prioritized over gbmap scans
(when they would gain knowledge). In theory this minimizes gc latency,
as gbmap scans risk triggering a full lookahead scan when building the
new gbmap.
---
Code changes minimal:
code stack ctx
before: 35152 2136 660
after: 35152 (+0.0%) 2136 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38076 2136 776
gbmap after: 38080 (+0.0%) 2136 (+0.0%) 776 (+0.0%)
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Christopher Haster
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7ccdee255b |
alloc: Reworked how lookahead/gbmap allocators interact
Before, the gbmap allocator worked by feeding the lookahead allocator,
so all allocation requests went through the lookahead buffer:
alloc ---> lookahead ---> gbmap
This worked, and was easy to strap on to the existing system, but
limited what we could cache to what fits in our lookahead buffer. This
doesn't have a big effect on runtime analysis, since fragmentation is
always a concern, but it does mean we're not taking advantage of the
gbmap range representation and accessing disk more than we need to.
It also limits in-use range skipping to a lookahead buffer at a time,
which is problematic as the whole reason for the gbmap is to make the
lookahead buffer mostly irrelevant.
On top of the range issues, this design makes it difficult to add
preerase info, which is coming up on the TODO list.
---
To fix this, I reorganized the two allocators to run in parallel, with
the gbmap being queried first before falling back to the lookahead
buffer:
alloc -+-> gbmap
'-> lookahead
Instead of relying on the lookahead buffer, the gbmap now stores one
range in the gbmap.free field, using the sign to indicate if it's free
vs in-use (not the best name, but oh well).
This adds a word of storage to the gbmap, but as a tradeoff we can track
a full region in RAM and avoid repeated gbmap lookups.
The lookahead buffer can still be populated by gc work, which may be
useful if the gbmap is exhausted, but will also be cleared during gbmap
allocations to avoid out-of-date state.
---
While reworking this, I also tweaked a number of other allocator things:
- Adjusted lookahead.window to point to next block candidate
(lookahead.window and gbmap.window should now always match)
- Renamed lfs3_alloc_zerogbmap -> lfs3_gbmap_zero
- Moved some alloc functions around
Code cost was mostly unaffected. Added an extra word to gbmap's ctx, but
as a tradeoff saved a chunk of stack by avoiding nested allocators:
code stack ctx
before: 35160 2136 660
after: 35152 (-0.0%) 2136 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38020 2152 772
gbmap after: 38076 (+0.1%) 2136 (-0.7%) 776 (+0.5%)
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Christopher Haster
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465e9fbe9d |
Reverted best-effort fsinfo.known_free/inuse prototype
See previous commit for motivation.
I can't think of how you could easily find this information from the
gbmap during/after mount, short of a O(d log_b d) scan through the
gbmap. Maybe useful, but probably not a great tradeoff for what is only
debug/diagnostic information.
So reverting, but maybe interesting to explore in the future with other
debug APIs.
Code changes:
code stack ctx
before: 35220 2136 660
after: 35160 (-0.2%) 2136 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38116 2152 776
gbmap after: 38020 (-0.3%) 2152 (+0.0%) 772 (-0.5%)
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Christopher Haster
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0b48faf898 |
Started prototyping best-effort fsinfo.known_free/inuse fields
The idea here was that we could provide best-effort known in-use/free
block info (and eventually pre-erased and bad block info) as a cheaper
alternative to lfs3_fs_usage. It's probably still not what users expect
from lfs3_fs_stat, but may be useful as debug/diagnostic info:
- fsinfo.known_free - Number of known free blocks
- fsinfo.known_inuse - Number of known in-use blocks
- fsinfo.known_preerased* - Number of pre-erased blocks
- fsinfo.known_bad* - Number of bad blocks
- fsinfo.block_count-(all of the above) - Number of unknown blocks
But while known_free/known_inuse is easy enough to find from the
lookahead buffer, it's surprisingly tricky from the gbmap. The best
option I can think of requires scanning the gbmap in O(d log_b d) either
(1) during mount, (2) during mkconsistent, or (3) during lookahead
scans. And that much extra work for debug/diagnostic info seems like a
poor tradeoff.
Note, though, that after scanning once, in theory the info would be
~free to maintain during gbmap rebuilds.
Will revert.
Code changes:
code stack ctx
before: 35160 2136 660
after: 35220 (+0.2%) 2136 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38020 2152 772
gbmap after: 38116 (+0.3%) 2152 (+0.0%) 776 (+0.5%)
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Christopher Haster
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1abd9d732f |
Tried to use correct types for cfg/fsinfo things
In theory, lfs3_size_t should be used for in-block sizes (though this is also mixed up with in-device sizes?), lfs3_off_t for file sizes, and lfs3_block_t for block counts (I don't think lfs3_off_t/lfs3_block_t will ever differ, but the notation is helpful). Though I've not done a great job at keeping these types organized... Changed: - cfg.block_count: lfs3_size_t -> lfs3_block_t - cfg.file_limit: lfs3_size_t -> lfs3_off_t - fsinfo.block_count: lfs3_size_t -> lfs3_block_t - fsinfo.file_limit: lfs3_size_t -> lfs3_off_t - lfs3_fs_usage: lfs3_ssize_t -> lfs3_sblock_t - geometry.block_size: lfs3_size_t -> lfs3_off_t - geometry.block_count: lfs3_size_t -> lfs3_block_t - and some internals No code changes. |
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Christopher Haster
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8db3ce342c |
rattrs: Replaced LFS3_tag_TAIL with single-recurse LFS3_tag_RATTRS
This originally started as an attempt to drop LFS3_tag_TAIL entirely,
but that didn't really go anywhere. Any attempt to work around the
double rattr-lists during mtree splits results in more mess than this
magic rattr.
But I did notice we only need to support "simple" rattrs during mtree
splits, which means we can just call lfs3_rbyd_appendrattrs to handle
these.
Maybe this will be problematic if we ever want to deduplicate
lfs3_mdir_commit___ and lfs3_rbyd_appendrattrs, but I don't see that
happening because of the different concerns (mdir-specific rattrs):
function code stack ctx
lfs3_mdir_commit___ 1052 744 396
lfs3_rbyd_appendrattrs 142 584 388
The benefit of a single-recurse LFS3_tag_RATTRS:
- Simplifies lfs3_mdir_commit__, no more awkward loop recursion.
- May have other use cases for nesting simple rattrs?
Adds a bit of code:
code stack ctx
before: 35316 2176 660
after: 35320 (+0.0%) 2176 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38148 2192 772
gbmap after: 38172 (+0.1%) 2192 (+0.0%) 772 (+0.0%)
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Christopher Haster
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ce6cbc3c77 |
rattrs: Allowed LFS3_RATTR_TAIL as alternate rattr-list terminator
LFS3_tag_RATTRS, now LFS3_tag_TAIL, is a bit funny in that it only
supports tail-recursive rattrs. The whole point of littlefs is
bounded-RAM after all. And if we know LFS3_tag_TAIL will terminate an
rattr-list, why bother with an additional LFS3_tag_NULL?
Like LFS3_RATTR_NULL, LFS3_RATTR_TAIL sets length=0 to indicate the end
of the rattr-lists.
Saves a bit of code:
code stack ctx
before: 35324 2176 660
after: 35316 (-0.0%) 2176 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38156 2192 772
gbmap after: 38148 (-0.0%) 2192 (+0.0%) 772 (+0.0%)
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Christopher Haster
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dca915dd95 |
rattrs: Converted rattrs to full variable-length isa
It's funny to see what originally started as a simple list of rbyd attrs
slowly morph into a full isa. But it makes sense. What we really want is
an abstract description of operations that can be played and replayed as
necessary to atomically update the mtree.
Using a fixed lfs3_rattr_t struct to represent this in C is easy, and
avoids strict-aliasing issues, but ultimately limited when it comes to
the wide-range of data we want to attach to attributes.
Unlike a computer's isa, we want to be able to include full 12-24 byte
branch pointers directly in the instruction!
---
So here's a full variable-length isa organized by words (max(uintptr_t,
uint32_t)).
The first 32-bit word extends the 16-bit tag with an extra 16-bits of
control information:
wwll llff ffcc cccc tttt tttt tttt tttt
^'-.-''-.-''--.--' : :
'--|----|-----|----:-----------------:-- compressed weight
:: '----|-----|----:-----------------:-- total len
:: '-----|----:-----------------:-- from encoder
:: '----:-----------------:-- optional count
:: rgmm kkkk -kkk kkkk
11 => w=-1 ^^ ^ '-.' '---.---'
00 => w=0 '|-|---|------|------ rm bit
01 => w=+1 '-|---|------|------ grow bit
10 => w=attached '---|------|------ mask bits
'------|------ tag suptype
'------ tag subtype
The 4-bit length field always encodes the full length of the
instruction, including the instruction itself and optional weight. The
4-bit from + 6-bit count fields operate independently and tell
lfs3_rbyd_appendrattr_ how to actually encode the data related to the
instruction.
To work around strict-aliasing issues, complex structs are expected to
be broken down into words and reconstructed in lfs3_rbyd_appendrattr_.
Most of our structs are organized into words anyways. For example:
// new child
*r++ = LFS3_RATTR(5, LFS3_TAG_BRANCH, -2, LFS3_FROM_BRANCH);
*r++ = LFS3_RATTR_WEIGHT(+child_->weight);
*r++ = LFS3_RATTR_ARG(child_->blocks[0]);
*r++ = LFS3_RATTR_ARG(child_->trunk);
*r++ = LFS3_RATTR_ARG(child_->cksum);
This also changes rattr-lists to be null-terminated, which makes a bit
more sense in a variable-length isa:
*r++ = LFS3_RATTR_NULL; // all zeros, including length
One concern with null-terminated rattr-lists is how easy it is to
forget the null-terminator, but an assert that all non-null rattrs have
non-zero length seemed to catch the many many mistakes during adoption.
Alternatively, separate LFS3_FROM_NULL/LFS3_FROM_NIL from fields could
be used if encoding space gets tight.
I'm also quite happy with the 2-bit weight feild, which allows omitting
the optional weight word for -1,0,+1 weights. These should cover at
least all mdir operations.
Note the exact encoding of the rattr fields is less of a concern than
the tag fields, as it doesn't reside on-disk can be changed on whim.
---
Saves a nice chunk of code and stack:
code stack ctx
before: 35920 2280 660
after: 35324 (-1.7%) 2176 (-4.6%) 660 (+0.0%)
code stack ctx
gbmap before: 38812 2296 772
gbmap after: 38156 (-1.7%) 2192 (-4.5%) 772 (+0.0%)
The stack savings are obvious, but the code savings a bit less so. A
variable length isa _is_ more complicated, but by limiting most encoding
decisions to compile-time (2-bit weights vs 32-bit weights for example),
the savings from fewer word manipulations on the stack wins.
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Christopher Haster
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cf34ba9aca |
Rearranged tag encodings, reserved suptype=0 for internal tags
This was motivated by a discussion with a gh user, in which it was noted
that not having a reserved suptype for internal tags risks potential
issues with long-term future tag compatibility.
I think the risk is low, but, without a reserved suptype, it _is_
possible for a future tag to conflict with an internal tag in an older
driver version, potentially and unintentionally breaking compatibility.
Note this is especially concerning during mdir compactions, where we
copy tags we may not understand otherwise.
In littlefs2 we reserved suptype=0x100, though this was mostly an
accident due to saturating the 3-bit suptype space. With the larger tag
space in littlefs3, the reserved suptype=0x100 was dropped.
---
Long story short, this reserves suptype=0 for internal flags (well, and
null, which is _mostly_ internal only, but does get written to disk as
unreachable tags).
Unfortunately, adding a new suptype _did_ require moving a bunch of
stuff around:
LFS3_TAG_NULL 0x0000 v--- ---- +--- ----
LFS3_TAG_INTERNAL 0x00tt v--- ---- +ttt tttt
LFS3_TAG_CONFIG 0x01tt v--- ---1 +ttt tttt
LFS3_TAG_MAGIC 0x0131 v--- ---1 +-11 --rr
LFS3_TAG_VERSION 0x0134 v--- ---1 +-11 -1--
LFS3_TAG_RCOMPAT 0x0135 v--- ---1 +-11 -1-1
LFS3_TAG_WCOMPAT 0x0136 v--- ---1 +-11 -11-
LFS3_TAG_OCOMPAT 0x0137 v--- ---1 +-11 -111
LFS3_TAG_GEOMETRY 0x0138 v--- ---1 +-11 1---
LFS3_TAG_NAMELIMIT 0x0139 v--- ---1 +-11 1--1
LFS3_TAG_FILELIMIT 0x013a v--- ---1 +-11 1-1-
LFS3_TAG_ATTRLIMIT? 0x013b v--- ---1 +-11 1-11
LFS3_TAG_GDELTA 0x02tt v--- --1- +ttt tttt
LFS3_TAG_GRMDELTA 0x0230 v--- --1- +-11 ----
LFS3_TAG_GBMAPDELTA 0x0234 v--- --1- +-11 -1rr
LFS3_TAG_GDDTREEDELTA* 0x0238 v--- --1- +-11 1-rr
LFS3_TAG_GPTREEDELTA* 0x023c v--- --1- +-11 11rr
LFS3_TAG_NAME 0x03tt v--- --11 +ttt tttt
LFS3_TAG_BNAME 0x0300 v--- --11 +--- ----
LFS3_TAG_REG 0x0301 v--- --11 +--- ---1
LFS3_TAG_DIR 0x0302 v--- --11 +--- --1-
LFS3_TAG_STICKYNOTE 0x0303 v--- --11 +--- --11
LFS3_TAG_BOOKMARK 0x0304 v--- --11 +--- -1--
LFS3_TAG_SYMLINK? 0x0305 v--- --11 +--- -1-1
LFS3_TAG_SNAPSHOT? 0x0306 v--- --11 +--- -11-
LFS3_TAG_MNAME 0x0330 v--- --11 +-11 ----
LFS3_TAG_DDNAME* 0x0350 v--- --11 +1-1 ----
LFS3_TAG_DDTOMB* 0x0351 v--- --11 +1-1 ---1
LFS3_TAG_STRUCT 0x04tt v--- -1-- +ttt tttt
LFS3_TAG_BRANCH 0x040r v--- -1-- +--- --rr
LFS3_TAG_DATA 0x0404 v--- -1-- +--- -1--
LFS3_TAG_BLOCK 0x0408 v--- -1-- +--- 1err
LFS3_TAG_DDKEY* 0x0410 v--- -1-- +--1 ----
LFS3_TAG_DID 0x0420 v--- -1-- +-1- ----
LFS3_TAG_BSHRUB 0x0428 v--- -1-- +-1- 1---
LFS3_TAG_BTREE 0x042c v--- -1-- +-1- 11rr
LFS3_TAG_MROOT 0x0431 v--- -1-- +-11 --rr
LFS3_TAG_MDIR 0x0435 v--- -1-- +-11 -1rr
LFS3_TAG_MSHRUB+ 0x0438 v--- -1-- +-11 1---
LFS3_TAG_MTREE 0x043c v--- -1-- +-11 11rr
LFS3_TAG_BMRANGE 0x044u v--- -1-- +1-- ++uu
LFS3_TAG_BMFREE 0x0440 v--- -1-- +1-- ----
LFS3_TAG_BMINUSE 0x0441 v--- -1-- +1-- ---1
LFS3_TAG_BMERASED 0x0442 v--- -1-- +1-- --1-
LFS3_TAG_BMBAD 0x0443 v--- -1-- +1-- --11
LFS3_TAG_DDRC* 0x0450 v--- -1-- +1-1 ----
LFS3_TAG_DDPCOEFF* 0x0451 v--- -1-- +1-1 ---1
LFs3_TAG_PCOEFFMAP* 0x0460 v--- -1-- +11- ----
LFS3_TAG_ATTR 0x06aa v--- -11a +aaa aaaa
LFS3_TAG_UATTR 0x06aa v--- -11- +aaa aaaa
LFS3_TAG_SATTR 0x07aa v--- -111 +aaa aaaa
LFS3_TAG_SHRUB 0x1kkk v--1 kkkk +kkk kkkk
LFS3_TAG_ALT 0x4kkk v1cd kkkk +kkk kkkk
LFS3_TAG_CKSUM 0x300p v-11 ---- ++++ +pqq
LFS3_TAG_NOTE 0x3100 v-11 ---1 ++++ ++++
LFS3_TAG_ECKSUM 0x3200 v-11 --1- ++++ ++++
LFS3_TAG_GCKSUMDELTA 0x3300 v-11 --11 ++++ ++++
* Planned
+ Reserved
? Hypothetical
Some additional notes:
- I was on the fence on keeping the 0x30 prefix on config tags now that
it is not longer needed to differentiate from null, but ultimately
decided to keep it because: 1. it's fun, 2. it decreases the chance
of false positives, 3. it keeps the redund bits readable in hexdumps,
and 4. it reserves some tags < config, which is useful since order
matters.
Instead, I pushed the 0x30 prefix to _more_ tags, mainly gstate.
As a coincidence, meta related tags (MNAME, MROOT, MRTREE) all shifted
to also have the 0x30 prefix, which is a nice bit of unexpected
consistency.
- I also considered reserving the redund bits across the config tags
similarly to what we've done in struct/gstate tags, but decided
against it as 1. it significantly reduces the config tag space
available, and 2. makes alignment with VERSION + R/W/OCOMPAT a bit
awkward.
Instead I think would should relax the redund bit alignment in other
suptypes, though in practice the intermixing of non-redund and redund
tags makes this a bit difficult.
Maybe we should consider including redund bits as a hint for things
like DATA? DDKEY? BSHRUB? etc?
- I created a bit more space for file btree struct tags, allowing for
both the future planned DDKEY, and BLOCK with optional erased-bit. We
don't currently use this, but it may be useful for the future planned
gddtree, which in-theory can track erased-state in partially written
file blocks.
Currently tracking erased-state in file blocks is difficult due to
the potential of multiple references, and inability to prevent ecksum
conflicts in raw data blocks.
- UATTR/SATTR bumped up to 0x600/0x700 to keep the 1-bit alignment,
leaving the suptype 0x500 unused. Though this may be useful if we ever
run out of struct tags (suptype=0x400), which is likely where most new
tags will go.
---
Code changes were minimal, but with a bunch of noise:
code stack ctx
before: 35912 2280 660
after: 35920 (+0.0%) 2280 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38800 2296 772
gbmap after: 38812 (+0.0%) 2296 (+0.0%) 772 (+0.0%)
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Christopher Haster
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c16c4a00d3 |
ck: Merged FSCK+CK -> CK flag namespace
Unintentionally arriving at the infamous "fsck" name is a bit funny. But it's probably something we don't want to conflict with if we can help it, on the off chance we want a sort of lfs3_fsck function in the future. (This is all hypothetical, but lfs3_fsck may expect an unmounted filesystem, and have a much larger scope than lfs3_fs_ck. Though typing this out now I'm realizing how confusing that might be...) Since lfs3_file_ck and lfs3_fs_ck share a subset of flags, it's not _entirely_ unreasonable for lfs3_file_ck and lfs3_fs_ck to share the same namespace. There's a risk of confusing users around what flags lfs3_file_ck accepts, but we have asserts, and said flags (LFS3_CK_MKCONSISTENT, LFS3_CK_LOOKAHEAD, etc) just don't really make sense in lfs3_file_ck: fs file y LFS3_CK_MKCONSISTENT 0x00000800 Make the filesystem consistent y LFS3_CK_LOOKAHEAD 0x00001000 Repopulate lookahead buffer y LFS3_CK_LOOKGBMAP 0x00002000 Repopulate the gbmap y LFS3_CK_PREERASE* 0x00004000 Pre-erase unused blocks y LFS3_CK_COMPACTMETA 0x00008000 Compact metadata logs y y LFS3_CK_CKMETA 0x00010000 Check metadata checksums y y LFS3_CK_CKDATA 0x00020000 Check metadata + data checksums y y LFS3_CK_REPAIRMETA* 0x00040000 Repair data blocks y y LFS3_CK_REPAIRDATA* 0x00080000 Repair metadata + data blocks * Planned Another option would be to document that lfs3_fs_ck accepts both LFS3_CK_* _and_ LFS3_GC_* flags, but I worry that would be more confusing. It would also lock us into supporting all LFs3_GC_* flags in lfs3_fs_ck, which may not always be the case. Though this is an argument for doing away with the whole LFS3_M/F/CK/GC/I_* duplication... (tbh another reason for this is to reduce the number of namespaces by at least one). No code changes. |
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|
Christopher Haster
|
5c0cebb00b |
ck: Traded ckmeta/ckdata for flag-based ck functions
TLDR: Replaced lfs3_file_ckmeta/ckdata and lfs3_fs_ckmeta/ckdata with
flag based ck functions:
- lfs3_file_ckmeta -> lfs3_file_ck + LFS3_CK_CKMETA
- lfs3_file_ckdata -> lfs3_file_ck + LFS3_CK_CKDATA
- lfs3_fs_ckmeta -> lfs3_fs_ck + LFS3_FSCK_CKMETA
- lfs3_fs_ckdata -> lfs3_fs_ck + LFS3_FSCK_CKDATA
Note lfs3_fs_ck is equivalent to lfs3_fs_gc, but:
1. Performs the work in one call (equivalent to littlefs2's lfs2_fs_gc)
2. Takes flags at call time (like lfs3_mount) instead of cfg time (like
lfs3_fs_gc)
3. Avoids the constant RAM necessary to track incremental GC state
---
Motivation:
I've been thinking: It's a bit weird that users are able to one-shot
janitorial work in lfs3_mount, but there's no equivalent function after
the filesystem is mounted.
Originally this is what lfs3_fs_gc was for, but after adding support for
incremental GC, it made sense to hide lfs3_fs_gc behind the opt-in
LFS3_GC ifdef due to the extra (ironically non-gc-able) state.
In theory lfs3_trv_t fills a bit of the gap, but, without the internal
i_flag handling and traversal restarts, it's a bit hard to use. And
basically requires duplicating said log, which we need anyways for
lfs3_mount!
So ideally we'd add an explicit one-shot GC function, but now lfs3_fs_gc
is taken.
While thinking about alternative names, I realized we can just call this
lfs3_fs_ck and completely replace lfs3_fs_ckmeta/ckdata.
This has some extra benefits:
- Avoids an explosion of ckmeta/ckdata/repairmeta/repairdata functions
- Discourages redundant traversals that could accomplish more work
- Makes it less confusing that ckdata implies ckmeta
---
I also tweaked lfs3_file_ck to match, but note that lfs3_file_ck is
internally very different from lfs3_fs_ck. For one, lfs3_file_ck only
supports "actual" check flags (LFS3_CK_*) vs all gc flags (LFS3_FSCK_*):
lfs3_file_ck:
LFS3_CK_CKMETA 0x00010000 Check metadata checksums
LFS3_CK_CKDATA 0x00020000 Check metadata + data checksums
LFS3_CK_REPAIRMETA* 0x00040000 Repair metadata blocks
LFS3_CK_REPAIRDATA* 0x00080000 Repair metadata + data blocks
* Planned
lfs3_fs_ck:
LFS3_FSCK_MKCONSISTENT 0x00000800 Make the filesystem consistent
LFS3_FSCK_LOOKAHEAD 0x00001000 Repopulate lookahead buffer
LFS3_FSCK_LOOKGBMAP 0x00002000 Repopulate the gbmap
LFS3_FSCK_PREERASE* 0x00004000 Pre-erase unused blocks
LFS3_FSCK_COMPACTMETA 0x00008000 Compact metadata logs
LFS3_FSCK_CKMETA 0x00010000 Check metadata checksums
LFS3_FSCK_CKDATA 0x00020000 Check metadata + data checksums
LFS3_FSCK_REPAIRMETA* 0x00040000 Repair metadata blocks
LFS3_FSCK_REPAIRDATA* 0x00080000 Repair metadata + data blocks
* Planned
As a plus, this also saves a bit of code:
code stack ctx
before: 35968 2280 660
after: 35924 (-0.1%) 2280 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38828 2296 772
gbmap after: 38812 (-0.0%) 2296 (+0.0%) 772 (+0.0%)
|
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|
Christopher Haster
|
867d201bce |
Bumped seek whence up to uint32_t
I can't think of a reason this should be uint8_t. Bumping it up to uint32_t matches the type used for other flags (even though whence is arguably not flags in a strict sense). No code changes. |
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|
Christopher Haster
|
ca678538d4 |
Adopted lowercase => internal pattern for LFS3_tag_* tags
This includes the mask/rm/grow bits: - LFS3_tag_RM - LFS3_tag_GROW - LFS3_tag_MASK0/2/8/12 Our in-device only handle types: - LFS3_tag_ORPHAN - LFS3_tag_TRV - LFS3_tag_UNKNOWN And in-device only tags with special behavior: - LFS3_tag_INTERNAL - LFS3_tag_RATTRS - LFS3_tag_SHRUBCOMMIT - LFS3_tag_GRMPUSH - LFS3_tag_MOVE - LFS3_tag_ATTRS Usually I'm not a big fan of case-sensitive naming patterns, but this has been useful for self-documenting what compat flags are in-device only. Might as well extend the idea to our tag definitions. |
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|
Christopher Haster
|
0f30021a0d |
Moved most on-disk definitions into lfs3.h
Having on-disk definitions in one place is useful for referencing them later, even if they aren't relevant for most API users. .h files in C are already forced to expose a bunch of internal details anyways, in order to provide struct size/alignment. Might as well include on-disk information that would have even bigger consequences if it changed. Moved: - Compat flag definitions - Tag definitions - DSIZEs and relevant encoding comments - Note some of these were already required to define lfs3_t |
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|
Christopher Haster
|
8233ac9dfe |
Renamed RELOOKAHEAD -> LOOKAHEAD, REGBMAP -> LOOKGBMAP
Yeah, after using these for a bit, the RE* names were not great. Trying LOOK* now, as an alternative that hopefully still implies the similar behavior without needing an additional prefix for LOOKAHEAD: - LFS3_*_RELOOKAHEAD -> LFS3_*_LOOKAHEAD - LFS3_*_REGBMAP -> LFS3_*_LOOKGBMAP - cfg.regbmap_thresh -> cfg.lookgbmap_thresh - cfg.gc_relookahead_thresh -> cfg.gc_lookahead_thresh - cfg.gc_regbmap_thresh -> cfg.gc_lookgbmap_thresh |
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|
Christopher Haster
|
4ccc8dc120 |
Added support for all mount-traversal flags in lfs3_format
I mean, why not? These redirect to the same internal lfs3_fs_gc_ function anyways. Might as well keep things consistent. Added: LFS3_F_MKCONSISTENT 0x00000800 Make the filesystem consistent LFS3_F_RELOOKAHEAD 0x00001000 Repopulate lookahead buffer LFS3_F_MKCONSISTENT is guaranteed to be a noop, but LFS3_F_RELOOKAHEAD forces a filesystem traversal, which may have some niche use case. No code changes. |
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|
Christopher Haster
|
b01a385bc9 |
Added LFS3_F_REGBMAP and LFS3_F_COMPACTMETA
These are unlikely to make much progress, but that doesn't seem like a great reason to disallow these flags in lfs3_format: LFS3_F_REGBMAP 0x00002000 Repopulate the gbmap LFS3_F_COMPACTMETA 0x00008000 Compact metadata logs These are actually guaranteed to do _no_ work when formatting _without_ the gbmap, but with the gbmap it's less clear. Looking forward to the planned ckfactory feature, these may be useful for cleaning up any rbyd commits created as a part of building the initial gbmap. --- Also tweaked the formatting for LFS3_F_* flags a bit, including making all ifdefs explicit (mainly ifdef LFS3_RDONLY). Mixed ifdefs are a real pain to read. No code changes. |
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|
Christopher Haster
|
9e75138f7a |
Rearranged O/M/F/GC/I flags
Now that we don't need to encode tstate info in our traversal flags, we
can move things around to be a bit more comfortable.
This is also after some tweaking to make space for planned features:
O flags:
O_MODE 0x00000003 ---- ---- ---- ---- ---- ---- ---- --11
O_RDONLY 0x00000000 ---- ---- ---- ---- ---- ---- ---- ----
O_WRONLY 0x00000001 ---- ---- ---- ---- ---- ---- ---- ---1
O_RDWR 0x00000002 ---- ---- ---- ---- ---- ---- ---- --1-
O_CREAT 0x00000004 ---- ---- ---- ---- ---- ---- ---- -1--
O_EXCL 0x00000008 ---- ---- ---- ---- ---- ---- ---- 1---
O_TRUNC 0x00000010 ---- ---- ---- ---- ---- ---- ---1 ----
O_APPEND 0x00000020 ---- ---- ---- ---- ---- ---- --1- ----
O_FLUSH 0x00000040 ---- ---- ---- ---- ---- ---- -1-- ----
O_SYNC 0x00000080 ---- ---- ---- ---- ---- ---- 1--- ----
O_DESYNC 0x00100000 ---- ---- ---1 ---- ---- ---- ---- ----
O_DEDAG* 0x00000100 ---- ---- ---- ---- ---- ---1 ---- ----
O_DEDUP* 0x00000200 ---- ---- ---- ---- ---- --1- ---- ----
O_COMPR? 0x00000400 ---- ---- ---- ---- ---- -1-- ---- ----
O_CKMETA 0x00010000 ---- ---- ---- ---1 ---- ---- ---- ----
O_CKDATA 0x00020000 ---- ---- ---- --1- ---- ---- ---- ----
O_REPAIRMETA* 0x00040000 ---- ---- ---- -1-- ---- ---- ---- ----
O_REPAIRDATA* 0x00080000 ---- ---- ---- 1--- ---- ---- ---- ----
o_WRSET 0x00000003 ---- ---- ---- ---- ---- ---- ---- --11
o_TYPE 0xf0000000 1111 ---- ---- ---- ---- ---- ---- ----
o_ZOMBIE 0x08000000 ---- 1--- ---- ---- ---- ---- ---- ----
o_UNCREAT 0x04000000 ---- -1-- ---- ---- ---- ---- ---- ----
o_UNSYNC 0x02000000 ---- --1- ---- ---- ---- ---- ---- ----
o_UNCRYST 0x01000000 ---- ---1 ---- ---- ---- ---- ---- ----
o_UNGRAFT 0x00800000 ---- ---- 1--- ---- ---- ---- ---- ----
o_UNFLUSH 0x00400000 ---- ---- -1-- ---- ---- ---- ---- ----
* Planned
? Hypothetical
T flags:
T_MODE 0x00000001 ---- ---- ---- ---- ---- ---- ---- ---1
T_RDONLY 0x00000000 ---- ---- ---- ---- ---- ---- ---- ----
T_RDWR 0x00000001 ---- ---- ---- ---- ---- ---- ---- ---1
T_MTREEONLY 0x00000002 ---- ---- ---- ---- ---- ---- ---- --1-
T_EXCL 0x00000008 ---- ---- ---- ---- ---- ---- ---- 1---
T_MKCONSISTENT 0x00000800 ---- ---- ---- ---- ---- 1--- ---- ----
T_RELOOKAHEAD 0x00001000 ---- ---- ---- ---- ---1 ---- ---- ----
T_REGBMAP 0x00002000 ---- ---- ---- ---- --1- ---- ---- ----
T_PREERASE* 0x00004000 ---- ---- ---- ---- -1-- ---- ---- ----
T_COMPACTMETA 0x00008000 ---- ---- ---- ---- 1--- ---- ---- ----
T_CKMETA 0x00010000 ---- ---- ---- ---1 ---- ---- ---- ----
T_CKDATA 0x00020000 ---- ---- ---- --1- ---- ---- ---- ----
T_REPAIRMETA* 0x00040000 ---- ---- ---- -1-- ---- ---- ---- ----
T_REPAIRDATA* 0x00080000 ---- ---- ---- 1--- ---- ---- ---- ----
t_EVICT* 0x00000010 ---- ---- ---- ---- ---- ---- ---1 ----
t_TYPE 0xf0000000 1111 ---- ---- ---- ---- ---- ---- ----
t_ZOMBIE 0x08000000 ---- 1--- ---- ---- ---- ---- ---- ----
t_CKPOINTED 0x04000000 ---- -1-- ---- ---- ---- ---- ---- ----
t_DIRTY 0x02000000 ---- --1- ---- ---- ---- ---- ---- ----
t_STALE 0x01000000 ---- ---1 ---- ---- ---- ---- ---- ----
t_BTYPE 0x00f00000 ---- ---- 1111 ---- ---- ---- ---- ----
* Planned
M/F flags:
M_MODE 0x00000001 ---- ---- ---- ---- ---- ---- ---- ---1
M_RDWR 0x00000000 ---- ---- ---- ---- ---- ---- ---- ----
M_RDONLY 0x00000001 ---- ---- ---- ---- ---- ---- ---- ---1
M_STRICT? 0x00000002 ---- ---- ---- ---- ---- ---- ---- --1-
M_FORCE? 0x00000004 ---- ---- ---- ---- ---- ---- ---- -1--
M_FORCEWITHRECKLESSABANDON?
0x00000008 ---- ---- ---- ---- ---- ---- ---- 1---
M_FLUSH 0x00000040 ---- ---- ---- ---- ---- ---- -1-- ----
M_SYNC 0x00000080 ---- ---- ---- ---- ---- ---- 1--- ----
M_DEDAG* 0x00000100 ---- ---- ---- ---- ---- ---1 ---- ----
M_DEDUP* 0x00000200 ---- ---- ---- ---- ---- --1- ---- ----
M_COMPR? 0x00000400 ---- ---- ---- ---- ---- -1-- ---- ----
M_REVDBG 0x00000010 ---- ---- ---- ---- ---- ---- ---1 ----
M_REVNOISE 0x00000020 ---- ---- ---- ---- ---- ---- --1- ----
M_CKPROGS 0x00100000 ---- ---- ---1 ---- ---- ---- ---- ----
M_CKFETCHES 0x00200000 ---- ---- --1- ---- ---- ---- ---- ----
M_CKMETAPARITY 0x00400000 ---- ---- -1-- ---- ---- ---- ---- ----
M_CKMETAREDUND* 0x00800000 ---- ---- 1--- ---- ---- ---- ---- ----
M_CKDATACKSUMS 0x01000000 ---- ---1 ---- ---- ---- ---- ---- ----
M_CKREADS* 0x01800000 ---- ---1 1--- ---- ---- ---- ---- ----
M_MKCONSISTENT 0x00000800 ---- ---- ---- ---- ---- 1--- ---- ----
M_RELOOKAHEAD 0x00001000 ---- ---- ---- ---- ---1 ---- ---- ----
M_REGBMAP 0x00002000 ---- ---- ---- ---- --1- ---- ---- ----
M_PREERASE* 0x00004000 ---- ---- ---- ---- -1-- ---- ---- ----
M_COMPACTMETA 0x00008000 ---- ---- ---- ---- 1--- ---- ---- ----
M_CKMETA 0x00010000 ---- ---- ---- ---1 ---- ---- ---- ----
M_CKDATA 0x00020000 ---- ---- ---- --1- ---- ---- ---- ----
M_REPAIRMETA* 0x00040000 ---- ---- ---- -1-- ---- ---- ---- ----
M_REPAIRDATA* 0x00080000 ---- ---- ---- 1--- ---- ---- ---- ----
F_CKFACTORY* 0x00000002 ---- ---- ---- ---- ---- ---- ---- --1-
F_GBMAP 0x02000000 ---- --1- ---- ---- ---- ---- ---- ----
F_GDDTREE* 0x04000000 ---- -1-- ---- ---- ---- ---- ---- ----
F_GPTREE* 0x08000000 ---- 1--- ---- ---- ---- ---- ---- ----
F_METAR1* 0x10000000 ---1 ---- ---- ---- ---- ---- ---- ----
F_METAR2* 0x20000000 --1- ---- ---- ---- ---- ---- ---- ----
F_METAR3* 0x30000000 --11 ---- ---- ---- ---- ---- ---- ----
F_DATAR1* 0x40000000 -1-- ---- ---- ---- ---- ---- ---- ----
F_DATAR2* 0x80000000 1--- ---- ---- ---- ---- ---- ---- ----
F_DATAR3* 0xc0000000 11-- ---- ---- ---- ---- ---- ---- ----
* Planned
? Hypothetical
It's a bit concerning that _all_ 32-bit mount flags end up used, but
what can you do...
Code changes minimal:
code stack ctx
before: 35964 2280 660
after: 35968 (+0.0%) 2280 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38828 2296 772
gbmap after: 38828 (+0.0%) 2296 (+0.0%) 772 (+0.0%)
|
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|
Christopher Haster
|
673fa7876f |
Reduced the scope of LFS3_REVDBG/REVNOISE
LFS3_REVDBG introduced a lot of overhead for something I'm not sure
anyone will actually use (I have enough tooling that the state of an
rbyd is rarely a mystery, see dbgbmap.py). That, and we're running out
of flags!
So this reduces LFS3_REVDBG to just store one of "himb" in the first
(lowest) byte of the revision count; information that is easily
available:
vvvv---- -------- -------- --------
vvvvrrrr rrrrrr-- -------- --------
vvvvrrrr rrrrrrnn nnnnnnnn nnnnnnnn
vvvvrrrr rrrrrrnn nnnnnnnn dddddddd
'-.''----.----''----.- - - '---.--'
'------|----------|----------|---- 4-bit relocation revision
'----------|----------|---- recycle-bits recycle counter
'----------|---- pseudorandom noise (if revnoise)
'---- h, i, m, or b (if revdbg)
-11-1--- - h = mroot anchor
-11-1--1 - i = mroot
-11-11-1 - m = mdir
-11---1- - b = btree node
Some other notes:
- Enabled LFS3_REVDBG and LFS3_REVNOISE to work together, now that
LFS3_REVDBG doesn't consume all unused rev bits.
Note that LFS3_REVDBG has priority over LFS3_REVNOISE, but _not_
recycle-bits, etc. Otherwise problems would happen for recycle-bits
>2^20 (though do we care?).
- Fixed an issue where using the gcksum as a noise source results in
noise=0 when there is only an mroot. This is due to how we xor out
the current mdir cksum during an mdir commit.
Fixed by using gcksum_p instead of gcksum.
- Added missing LFS3_I_REVDBG/REVNOISE flags in the tests, so now you
can actually run the tests with LFS3_REVDBG/REVNOISE (this probably
just fell out-of-date at some point).
---
Curiously, despite LFS3_REVDBG/REVNOISE being disabled by default, this
did save some code. I'm guessing the non-tail-call mtree/gbmap commit
functions prevented some level of inlining?:
code stack ctx
before: 35964 2280 660
after: 35964 (+0.0%) 2280 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38940 2296 772
gbmap after: 38828 (-0.3%) 2296 (+0.0%) 772 (+0.0%)
|
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|
Christopher Haster
|
4010afeafd |
trv: Reintroduced LFS3_T_EXCL
With the relaxation of traversal behavior under mutation, I think it
makes sense to bring back LFS3_T_EXCL. If only to allow traversals to
gaurantee termination under mutation. Now that traversals no longer
guarantee forward progress, it's possible to get stuck looping
indefinitely if the filesystem is constantly being mutated.
Non-excl traversals are probably still useful for GC work and debugging
threads, but LFS3_T_EXCL now allows traversals to terminate immediately
with LFS3_ERR_BUSY at the first sign of unrelated filesystem mutation:
LFS3_T_EXCL 0x00000008 Error if filesystem modified
Internally, we already track unrelated mutation to avoid corrupt state
(LFS3_t_DIRTY), so this is a very low-cost feature:
code stack ctx
before: 35944 2280 660
after: 35964 (+0.1%) 2280 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38916 2296 772
gbmap after: 38940 (+0.1%) 2296 (+0.0%) 772 (+0.0%)
code stack ctx
gc before: 36016 2280 768
gc after: 36036 (+0.1%) 2280 (+0.0%) 768 (+0.0%)
|
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|
Christopher Haster
|
e9f2944573 |
Renamed bshrub.shrub[_] -> bshrub.b[_]
Mostly for consistency with mtrv.b and gbmap.b, but also (1) this hopefully reduces confusion around the fact that these can refer to both bshrubs and btrees, and (2) saves a bit of typing with the messy struct namespaces forced by C's strict aliasing. |
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|
Christopher Haster
|
14c369af93 |
trv: Adopted LFS3_t_STALE for marking block queue as stale
This solves the previous gc-needs-block-queue-so-we-can-clobber-block-
queue issue by adding an additional LFS3_t_STALE flag to indicate when
any block queues would be invalid.
So instead of clearing block queues in lfs3_alloc_ckpoint, we just set
LFS3_t_STALE, and any lfs3_trv_ts can clear their block queues in
lfs3_trv_read. This allows lfs3_mgc_ts to be allocated without a block
queue when doing any LFS3_M_*/LFS3_F_*/LFS3_GC_* work.
LFS3_t_STALE is set at the same time as LFS3_t_CKPOINT and LFS3_t_DIRTY,
but we need a separate bit so lfs3_trv_read can clear the flag after
flushing without losing ckpoint/dirty information.
---
Unfortunately, none of the stack-allocated lfs3_mgc_ts are on the stack
hot-path, so we don't immediate savings. But note the 2-words saved in
ctx when compiling in LFS3_GC mode:
code stack ctx
before: 35940 2280 660
after: 35944 (+0.0%) 2280 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38916 2296 772
gbmap after: 38916 (+0.0%) 2296 (+0.0%) 772 (+0.0%)
code stack ctx
gc before: 36012 2280 776
gc after: 36016 (+0.0%) 2280 (+0.0%) 768 (-1.0%)
|
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|
Christopher Haster
|
d1d69c0a52 |
trv: Greatly simplified filesystem traversal
The main idea here is to drop the flag-encoded tstate state machine, and
replace it with a matrix controlled by special mid + bid values:
-- mid ->
-5 -4 -3 -2 >=-1
bid -2 x x x --> mdir
v >=-1 x gbm gbm x --> bshrub/btree
'----|----|----|----|----> mroot anchor
'----|----|----|----> mroot chain + mtree
'----|----|----> gbmap (in-ram gbmap)
'----|----> gbmap_p (on-disk gbmap)
'----> file bshrubs/btrees
This was motivated by the observation that everything in our filesystem
can be modeled as mdir + bshrub/btree tuples, as long as some states are
noops. And we can cleanly encode these tuples in the unused negative
mid + bid ranges without needing an explicit state machine.
Well, that and the previous tstate state machine approach being an ugly
pile of switch cases and messy logic.
Note though that some mids may need to traverse multiple mdirs/bshrub/
btrees:
- The mroot chain + mtree (mid=-4) needs to traverse all mroots in the
mroot chain, and detect any cycles.
- File mdirs (mid>=-1) need to traverse both the on-disk bshrub/btree
and any opened file handles' bshrubs/btrees before moving onto the
next mid.
This grows O(n^2) because all file handles are in one big unsorted
linked-list, but as usual we don't care.
In addition to the greatly simplified traversal logic, the new state
matrix simplifies traversal clobbering: Setting bid=-2 always forces a
bshrub/btree refetch.
This comes at the cost of traversal _precision_, i.e. we can now revisit
previously visited bshrub/btree nodes. But I think this is well worth it
for more robust traversal clobbering. Traversal clobbering is delicate
and difficult to get right.
Besides, we can already revisit blocks due to CoW references, so what's
the harm in revisiting blocks when under mutation?
---
The simpler traversal logic leads to a nice amount of code savings
across the board:
code stack ctx
before: 36476 2304 660
after: 35940 (-1.5%) 2280 (-1.0%) 660 (+0.0%)
code stack ctx
gbmap before: 39524 2320 772
gbmap after: 38916 (-1.5%) 2296 (-1.0%) 772 (+0.0%)
code stack ctx
gc before: 36548 2304 804
gc after: 36012 (-1.5%) 2280 (-1.0%) 776 (-3.5%)
Note the ctx savings in LFS3_GC mode. Most of the stack/ctx savings
comes from the smaller lfs3_mtrv_t struct, which no longer needs to
stage bshrubs (we no longer care about bshrubs across mdir commit as a
part of the above clobbering simplifications):
before after
lfs3_mtrv_t: 128 100 (-21.9%)
lfs3_mgc_t: 128 100 (-21.9%)
lfs3_trv_t: 136 108 (-20.6%)
Unfortunately, the simpler clobbering means now any gc work needs the
block queue (i.e. lfs3_trv_t), solely so clobbering the block queue
doesn't clobber unallocated memory. Not great but hopefully fixable.
---
Some other notes:
- As a part of simplifying traversal clobbering, everything is triggered
by lfs3_alloc_ckpoint (via lfs3_trv_ckpoint_).
This may clobber traversals more than is strictly necessary, but
that's kinda the idea. Better safe than sorry.
And no more need to explicit lfs3_handle_clobber calls is nice.
- Opened file handle iteration is now tracked by the traversal handle's
position in the handle linked-list, instead of a separate handle
pointer. This means one less thing to disentangle and makes traversals
no longer a special case for things like lfs3_handle_close.
You may think this bumps traversals up to O(n^3) in-ram, but because
we only ever visit each unique handle + mid once, we can keep the
total O(n^2) if we're smart about linked-list updates!
- lfs3_mdir_commit needed to be tweaked to accept mids<=-1, instead of
just mid=-1 for the mroot. Unfortunately I don't know how much this
costs on its own.
- The reorganization of lfs3_mtrv_t means lfs3_mtortoise_t gets its own
struct again!
- No more tstate state machine also frees up a big chunk of the
traversal flag space, which was getting pretty cramped.
|
||
|
Christopher Haster
|
a01b1b73b2 |
btree: Moved leaf caching behind LFS3_BLEAFCACHE ifdef
This is motivated by the observation that the O(n log_b n) btree
iteration really just hasn't been a bottleneck in our benchmarks.
Our write performance is mostly dominated by compaction costs, and while
filesystem _traversals_ are a concern, it's easy to explicitly track
rbyds in lfs3_btrv_t.
Additionally:
- We track mdirs during mtree iteration, which are the true mtree
leaves.
- We already cache file leaves, i.e. bptrs and read-fragments.
On top of this, leaf caching adds complexity, both in terms of
code/stack costs, but also in terms of reliability. It introducing the
need for cache invalidation, which is infamously one of the two hard
problems in computer science!
This is the second(?) time btree leaf traversals have been reverted, so
see previous commit messages for even more arguments against.
---
Eventually, we should probably just delete the btree leaf cache logic to
avoid the maintenance headache (cache invalidation + opt+in/less
testing = ouch). But I want to do a bit more benchmarking comparing the
two modes, so just moving this behind an ifdef for now.
Saves code, and of course RAM:
code stack ctx
before btrv: 37160 2352 688
before: 37088 (-0.2%) 2384 (+1.4%) 688 (+0.0%)
after: 36480 (-1.8%) 2304 (-2.0%) 660 (-4.1%)
But note while this keeps the performance implications of btree leaf
caching, it does not keep the code/stack optimizations that internally
reuse the leaf cache for things (btrv, lookupnext_ rbyd side-channel,
etc).
In _theory_ these could have been kept with enough ifdefs, but it would
have made the codebase quite a bit of a hell to maintain:
code stack ctx
always-bleafcache: 37160 2352 688
no-bleafcache: 36480 (-1.8%) 2304 (-2.0%) 660 (-4.1%)
yes-bleafcache: 37044 (-0.3%) 2384 (+1.4%) 688 (+0.0%)
Gbmap mode has even more savings due to how many gbmap copies we have
flying around:
code stack ctx
gbmap + always-bleafcache: 40132 2368 856
gbmap + no-bleafcache: 39464 (-1.7%) 2320 (-2.0%) 772 (-9.8%)
gbmap + yes-bleafcache: 40052 (-0.2%) 2400 (+1.4%) 856 (+0.0%)
---
In the future, _maybe_ we can revisit this. But I think a better design
would be to cache btree leaves globally, in lfs3_t, similarly to the
theoretical mdir cache. This would allow a user-configurable number of
cached btree nodes, and may make cache invalidation easier.
Note, however, that btree nodes don't need to be fetched (even for
commits now!), so the benefits would be much smaller than for the
theoretical mdir cache.
But hey, it would defend the lack of low-level rbyd tracking during
iteration/rattr queries!
|
||
|
Christopher Haster
|
39a265ce90 |
btree: Dropped reliance on leaf cache during traversals
Brings back lfs3_btrv_t, but keeps some of the btree internal changes.
I think the biggest one is dropping the internal branch pointer, now
instead of internally pointing to the root rbyd, we just unconditionally
sync the rbyd state anytime the rbyd matches the root's weight. This is
necessary to avoid out-of-sync state when traversing bshrubs under
mutation.
Also after refactoring I think the current btree traversal logic is
easier to read.
---
This is in preparation for removing the leaf cache, or at least making
it opt-in.
It adds a chunk of stack, but in theory we can reclaim this by allowing
leaf caches to be disabled:
code stack ctx
before: 37160 2352 688
after: 37088 (-0.2%) 2384 (+1.4%) 688 (+0.0%)
|
||
|
Christopher Haster
|
5d905e6da4 |
Dropped LFS3_KVONLY and LFS3_2BONLY modes for now
I think these are good ideas to bring back when littlefs3 is more mature, but at the moment the number of different builds is creating too much friction. LFS3_KVONLY and LFS3_2BONLY in particular _add_ significant chunks of code (lfs3_file_readget_, lfs3_file_flushset_, and various extra logic sprinkled throughout the codebase), and the current state of testing means I have no idea if any of it still works. These are also low-risk for introducing any disk related changes. So, ripping out for now to keep the current experimental development tractable. May reintroduce in the future (probably after littlefs3 is stabilized) if there is sufficient user interest. But doing so will probably also need to come with actual testing in CI. |
||
|
Christopher Haster
|
207446223b |
rdonly: Fixed various LFS3_RDONLY compile errors
This just fell out-of-sync a bit during the gbmap work. Note we _do_
support LFS3_RDONLY + LFS3_GBMAP, as fetching the gbmap is necessary for
CKMETA to check all metadata. Fortunately this is relatively cheap:
code stack ctx
rdonly: 10716 896 532
rdonly+gbmap: 10988 (+2.5%) 896 (+0.0%) 680 (+27.8%)
Though this does highlight that a sort of LFS3_NO_TRV mode could remove
quite a bit of code.
|
||
|
Christopher Haster
|
3ab7ecb2b0 |
Renamed file_cache -> fcache and gbmap_re -> regbmap
This walks back some of the attempt at strict object namespacing in struct lfs3_cfg: - cfg.file_cache_size -> cfg.fcache_size - filecfg.cache_size -> filecfg.fcache_size - filecfg.cache_buffer -> filecfg.fcache_buffer - cfg.gbmap_re_thresh -> cfg.regbmap_thresh Motivation: - cfg.regbmap_thresh now matches cfg.gc_regbmap_thresh, instead of using awkwardly different namespacing patterns. - Giving fcache a more unique name is useful for discussion. Having pcache, rcache, and then file_cache was a bit awkward. Hopefully it's also more clear that cfg.fcache_size and filecfg.fcache_size are related. - Config in struct lfs3_cfg is named a bit more consistently, well, if you ignore gc_*_* options. - Less typing. Though this gets into pretty subjective naming territory. May revert this if the new terms are uncomfortable after use. |
||
|
Christopher Haster
|
b49d9e9ece |
Renamed REPOP* -> RE*
So: - cfg.gc_repoplookahead_thresh -> cfg.gc_relookahead_thresh - cfg.gc_repopgbmap_thresh -> cfg.gc_regbmap_thresh - cfg.gbmap_repop_thresh -> cfg.gbmap_re_thresh - LFS3_*_REPOPLOOKAHEAD -> LFS3_*_RELOOKAHEAD - LFS3_*_REPOPGBMAP -> LFS3_*_REGBMAP Mainly trying to reduce the mouthful that is REPOPLOOKAHEAD and REPOPGBMAP. As a plus this also avoids potential confusion of "repop" as a push/pop related operation. |
||
|
Christopher Haster
|
8a58954828 |
trv: Reduced LFS3_t_CKPOINTED + LFS3_t_MUTATED -> LFS3_t_CKPOINTED
This drops LFS3_t_MUTATED in favor of just using LFS3_t_CKPOINTED
everywhere:
1. These meant roughly the same thing, with LFS3_t_MUTATED being a bit
tighter at the cost of needing to be explicitly set.
2. The implicit setting of LFS3_t_CKPOINTED by lfs3_alloc_ckpoint -- a
function that already needs to be called before mutation -- means we
have one less thing to worry about.
Implicit properties like LFS3_t_CKPOINTED are great for building a
reliable system. Manual flags like LFS3_t_MUTATED, not so much.
3. Why use two flags when we can get away with one?
The only downside is we may unnecessarily clobber gc/traversal work when
we don't actually mutate the filesystem. Failed file open calls are a
good example.
However this tradeoff seems well worth it for an overall simpler +
more reliable system.
---
Saves a bit of code:
code stack ctx
before: 37220 2352 688
after: 37160 (-0.2%) 2352 (+0.0%) 688 (+0.0%)
code stack ctx
gbmap before: 40184 2368 856
gbmap after: 40132 (-0.1%) 2368 (+0.0%) 856 (+0.0%)
|
||
|
Christopher Haster
|
5d70e47708 |
trv: Reverted LFS3_t_NOSPC, forward gbmap repop errors
Note: This affects the blocking lfs3_alloc_repopgbmap as well as
incremental gc/traversal repopulations. Now all repop attempts return
LFS3_ERR_NOSPC when we don't have space for the gbmap, motivation below.
This reverts the previous LFS3_t_NOSPC soft error, in which traversals
were allowed to continue some gc/traversal work when encountering
LFS3_ERR_NOSPC. This results in a simpler implementation and fewer error
cases to worry about.
Observation/motivation:
- The main motivation is noticing that when we're in low-space
conditions, we just start spamming gbmap repops even if they all fail.
That's really not great! We might as well just mark the flash as dead
if we're going to start spamming erases!
At least with an error the user can call rmgbmap to try to make
progress.
- If we're in a low-space condition, something else will probably return
LFS3_ERR_NOSPC anyways. Might as well report this early and simplify
our system.
- It's a simpler model, and littlefs3 is already much more complicated
than littlefs2. Maybe we should lean more towards a simpler system
at the cost of some niche optimizations.
---
This had the side-effect of causing more lfs3_alloc_ckpoints to return
errors during testing, which revealed a bug in our uz/uzd_fuzz tests:
- We weren't flushing after writes to the opened RDWR files, which could
cause delayed errors to occur during the later read checks in the
test.
Fortunately LFS3_O_FLUSH provides a quick and easy fix!
Note we _don't_ adopt this in all uz/uzd_fuzz tests, only those that
error. It's good to test both with and without LFS3_O_FLUSH to test
that read-flushing also works under stress.
Saves a bit of code:
code stack ctx
before: 37260 2352 688
after: 37220 (-0.1%) 2352 (+0.0%) 688 (+0.0%)
code stack ctx
gbmap before: 40220 2368 856
gbmap after: 40184 (-0.1%) 2368 (+0.0%) 856 (+0.0%)
|
||
|
Christopher Haster
|
f892d299dd |
trv: Added LFS3_t_NOSPC, avoid ENOSPC errors in traversals
This relaxes error encountered during lfs3_mtree_gc to _not_ propagate,
but instead just log a warning and prevent the relevant work from being
checked off during EOT.
The idea is this allows other work to make progress in low-space
conditions.
I originally meant to limit this to gbmap repopulations, to match the
behavior of lfs3_alloc_repopgbmap, but I think extending the idea to all
filesystem mutating operations makes sense (LFS3_T_MKCONSISTENT +
LFS3_T_REPOPGBMAP + LFS3_T_COMPACTMETA).
---
To avoid incorrectly marking traversal work as completed, we need to
track if we hit any ENOSPC errors, thus the new LFS3_t_NOSPC flag:
LFS3_t_NOSPC 0x00800000 Optional gc work ran out of space
Not the happiest just throwing flags at problems, but I can't think of a
better solution at the moment.
This doesn't differentiate between ENOSPC errors during the different
types of work, but in theory if we're hitting ENOSPC errors whatever
work returns the error is a toss-up anyways.
---
Adds a bit of code:
code stack ctx
before: 37208 2352 688
after: 37248 (+0.1%) 2352 (+0.0%) 688 (+0.0%)
code stack ctx
gbmap before: 40120 2368 856
gbmap after: 40204 (+0.2%) 2368 (+0.0%) 856 (+0.0%)
|
||
|
Christopher Haster
|
12874bff76 |
gbmap: Added gc_repoplookahead_thresh and gc_repopgbmap_thresh
To allow relaxing when LFS3_I_REPOPLOOKAHEAD and LFS3_I_REPOPGBMAP will
be set, potentially reducing gc workload after allocating only a couple
blocks.
The relevant cfg comments have quite a bit more info.
Note -1 (not the default, 0, maybe we should explicitly flip this?)
restores the previous functionality of setting these flags on the first
block allocation.
---
Also tweaked gbmap repops during gc/traversals to _not_ try to repop
unless LFS3_I_REPOPGBMAP is set. We probably should have done this from
the beginning since repopulating the gbmap writes to disk and is
potentially destructive.
Adds code, though hopefully we can claw this back with future config
rework:
code stack ctx
before: 37176 2352 684
after: 37208 (+0.1%) 2352 (+0.0%) 688 (+0.6%)
code stack ctx
gbmap before: 40024 2368 848
gbmap after: 40120 (+0.2%) 2368 (+0.0%) 856 (+0.9%)
|
||
|
Christopher Haster
|
1dc1a26f11 |
gc: Added LFS3_GC_ALL to make running all gc work easier
This is an alias for all possible gc work, which is a bit more complicated than you might think due to compile-time features (example: LFS3_GC_REPOPGBMAP). The intention is to make loops like the following easy to write: struct lfs3_fsinfo fsinfo; lfs3_fs_stat(&lfs3, &fsinfo) => 0; lfs3_trv_t trv; lfs3_trv_open(&lfs3, &trv, fsinfo.flags & LFS3_GC_ALL) => 0; ... It's possible to do this by explicitly setting all gc flags, but that requires quite a bit of knowledge from the user. Another option is allowing -1 for gc/traversal flags, but that loses assert protection against unknown/misplaced flags. --- This raises more questions about the prefix naming: it feels a bit weird to take LFS3_I_* flags, mask with LFS3_GC_* flags, and pass them as LFS3_T_* flags, but it gets the job done. Limiting LFS3_GC_ALL to the LFS3_GC_* namespace avoids issues with opt-out/mode flags such as LFS3_T_RDONLY, LFS3_T_MTREEONLY, etc. For this reason it probably doesn't make sense to add something similar to the other namespaces. |
||
|
Christopher Haster
|
1f824a029b |
Renamed LFS3_T_COMPACT -> LFS3_T_COMPACTMETA (and gc_compactmeta_thresh)
- LFS3_T_COMPACT -> LFS3_T_COMPACTMETA - gc_compact_thresh -> gc_compactmeta_thresh And friends: LFS3_M_COMPACTMETA 0x00000800 Compact metadata logs LFS3_GC_COMPACTMETA 0x00000800 Compact metadata logs LFS3_I_COMPACTMETA 0x00000800 Filesystem may have uncompacted metadata LFS3_T_COMPACTMETA 0x00000800 Compact metadata logs --- This does two things: 1. Highlights that LFS3_T_COMPACTMETA only interacts with metadata logs, and has no effect on data blocks. 2. Better matches the verb+noun names used for other gc/traversal flags (REPOPGBMAP, CKMETA, etc). It is a bit more of a mouthful, but I'm not sure that's entirely a bad thing. These are pretty low-level flags. |
||
|
Christopher Haster
|
9bdfb25a09 |
Renamed LFS3_T_LOOKAHEAD -> LFS3_T_REPOPLOOKAHEAD
And friends: LFS3_M_REPOPLOOKAHEAD 0x00000200 Repopulate lookahead buffer LFS3_GC_REPOPLOOKAHEAD 0x00000200 Repopulate lookahead buffer LFS3_I_REPOPLOOKAHEAD 0x00000200 Lookahead buffer is not full LFS3_T_REPOPLOOKAHEAD 0x00000200 Repopulate lookahead buffer To match LFS3_T_REPOPGBMAP, which is more-or-less the same operation. Though this does turn into quite the mouthful... |
||
|
Christopher Haster
|
ced63a4c73 |
Renamed inline_size -> shrub_size
There's a strong argument for naming this inline_size as that's more likely what users expect, but shrub_size is just the more correct name and avoids confusion around having multiple names for the same thing. It also highlights that shrubs in littlefs3 are a bit different than inline files in littlefs2, and that this config also affects large files with a shrubbed root. May rerevert this in the future, but probably only if there is significant user confusion. |
||
|
Christopher Haster
|
3b4e1e9e0b |
gbmap: Renamed gbmap_rebuild_thresh -> gbmap_repop_thresh
And tweaked a few related comments. I'm still on the fence with this name, I don't think it's great, but it at least betters describes the "repopulation" operation than "rebuilding". The important distinction is that we don't throw away information. Bad/erased block info (future) is still carried over into the new gbmap snapshot, and persists unless you explicitly call rmgbmap + mkgbmap. So, adopting gbmap_repop_thresh for now to see if it's just a habit thing, but may adopt a different name in the future. As a plus, gbmap_repop_thresh is two characters shorter. |
||
|
Christopher Haster
|
fb90bf976c |
trv: Split lfs3_trv_t -> lfs3_trv_t, lfs3_mgc_t, and lfs3_mtrv_t
A big downside of LFS3_T_REBUILDGBMAP is the addition of an lfs3_btree_t
struct to _every_ traversal object.
Unfortunately, I don't see a way around this. We need to track the new
gbmap snapshot _somewhere_, and other options (such as a global gbmap.b_
snapshot) just move the RAM around without actually saving anything.
To at least mitigate this internally, this splits lfs3_trv_t into
distinct lfs3_trv_t, lfs3_mgc_t, and lfs3_mtrv_t structs that capture
only the relevant state for internal traversal layers:
- lfs3_mtree_traverse <- lfs3_mtrv_t
- lfs3_mtree_gc <- lfs3_mgc_t (contains lfs3_mtrv_t)
- lfs3_trv_read <- lfs3_trv_t (contains lfs3_mgc_t)
This minimizes the impact of the gbmap rebuild snapshots, and saves a
big chunk of RAM. As a plus it also saves RAM in the default build by
limiting the 2-block block queue to the high-level lfs3_trv_read API:
code stack ctx
before: 37176 2360 684
after: 37176 (+0.0%) 2352 (-0.3%) 684 (+0.0%)
code stack ctx
gbmap before: 40060 2432 848
gbmap after: 40024 (-0.1%) 2368 (-2.6%) 848 (+0.0%)
The main downside? Our field names are continuing in their
ridiculousness:
lfs3.gc.gc.t.b.h.flags // where else would the global gc flags be?
|
||
|
Christopher Haster
|
06bc4dff04 |
trv: Simplified MUTATED/DIRTY flags, no more swapping
A bit less simplified than I hoped, we don't _strictly_ need both
LFS3_t_DIRTY + LFS3_t_MUTATED if we're ok with either (1) making
multiple passes to confirm fixorphans succeeded or (2) clear the COMPACT
flag after one pass (which may introduce new uncompacted metadata). But
both of these have downsides, and we're not _that_ stressed for flag
space yet...
So keeping all three of:
LFS3_t_DIRTY 0x04000000 Filesystem modified outside traversal
LFS3_t_MUTATED 0x02000000 Filesystem modified during traversal
LFS3_t_CKPOINTED 0x01000000 Filesystem ckpointed during traversal
But I did manage to get rid of the bit swapping by tweaking LFS3_t_DIRTY
to imply LFS3_t_MUTATED instead of being exclusive. This removes the
"failed" gotos in lfs3_mtree_gc and makes things a bit more readable.
---
I also split lfs3_fs/handle_clobber into separate lfs3_fs/handle_clobber
and lfs3_fs/handle_mutate functions. This added a bit of code, but I
think is worth it for a simpler internal API. A confusing internal API
is no good.
In total these simplifications saved a bit of code:
code stack ctx
before: 37208 2360 684
after: 37176 (-0.1%) 2360 (+0.0%) 684 (+0.0%)
code stack ctx
gbmap before: 40100 2432 848
gbmap after: 40060 (-0.1%) 2432 (+0.0%) 848 (+0.0%)
|
||
|
Christopher Haster
|
f5508a1b6c |
gbmap: Added LFS3_T_REBUILDGBMAP and friends
This adds LFS3_T_REBUILDGBMAP and friends, and enables incremental gbmap
rebuilds as a part of gc/traversal work:
LFS3_M_REBUILDGBMAP 0x00000400 Rebuild the gbmap
LFS3_GC_REBUILDGBMAP 0x00000400 Rebuild the gbmap
LFS3_I_REBUILDGBMAP 0x00000400 The gbmap is not full
LFS3_T_REBUILDGBMAP 0x00000400 Rebuild the gbmap
On paper, this is more or less identical to repopulating the lookahead
buffer -- traverse the filesystem, mark blocks as in-use, adopt the new
gbmap/lookahead buffer on success -- but a couple nuances make
rebuilding the gbmap a bit trickier:
- Unlike the lookahead buffer, which eagerly zeros in allocation, we
need an explicit zeroing pass before we start marking blocks as
in-use. This means multiple traversals can potentially conflict with
each other, risking the adoption of a clobbered gbmap.
- The gbmap, which stores information on disk, relies on block
allocation and the temporary "in-flight window" defined by allocator
ckpoints to avoid circular block states during gbmap rebuilds. This
makes gbmap rebuilds sensitive to allocator ckpoints, which we
consider more-or-less a noop in other parts of the system.
Though now that I'm writing this, it might have been possible to
instead include gbmap rebuild snapshots in fs traversals... but that
would probably have been much more complicated.
- Rebuilding the gbmap requires writing to disk and is generally much
more expensive/destructive. We want to avoid trying to rebuild the
gbmap when it's not possible to actually make progress.
On top of this, the current trv-clobber system is a delicate,
error-prone mess.
---
To simplify everything related to gbmap rebuilds, I added a new
internal traversal flag: LFS3_t_CKPOINTED:
LFS3_t_CKPOINTED 0x04000000 Filesystem ckpointed during traversal
LFS3_t_CKPOINTED is set, unconditionally, on all open traversals in
lfs3_alloc_ckpoint, and provides a simple, robust mechanism for checking
if _any_ allocator checkpoints have occured since a traversal was
started. Since lfs3_alloc_ckpoint is required before any block
allocation, this provides a strong guarantee that nothing funny happened
to any allocator state during a traversal.
This makes lfs3_alloc_ckpoint a bit less cheap, but the strong
guarantees that allocator state is unmodified during traversal are well
worth it.
This makes both lookahead and gbmap passes simpler, safer, and easier to
reason about.
I'd like to adopt something similar+stronger for LFs3_t_MUTATED, and
reduce this back to two flags, but that can be a future commit.
---
Unfortunately due to the potential for recursion, this ended up reusing
less logic between lfs3_alloc_rebuildgbmap and lfs3_mtree_gc than I had
hoped, but at like the main chunks (lfs3_alloc_remap,
lfs3_gbmap_setbptr, lfs3_alloc_adoptgbmap) could be split out into
common functions.
The result is a decent chunk of code and stack, but the value is high as
incremental gbmap rebuilds are the only option to reduce the latency
spikes introduced by the gbmap allocator (it's not significantly worse
than the lookahead buffer, but both do require traversing the entire
filesystem):
code stack ctx
before: 37164 2352 684
after: 37208 (+0.1%) 2360 (+0.3%) 684 (+0.0%)
code stack ctx
gbmap before: 39708 2376 848
gbmap after: 40100 (+1.0%) 2432 (+2.4%) 848 (+0.0%)
Note the gbmap build is now measured with LFS3_GBMAP=1, instead of
LFS3_YES_GBMAP=1 (maybe-gbmap) as before. This includes the cost of
mkgbmap, lfs3_f_isgbmap, etc.
|
||
|
Christopher Haster
|
61dc21ccb7 |
gbmap: Renamed/moved lookahead.bmapped -> gbmap.known
And:
- Tweaked the behavior of gbmap.window/known to _not_ match disk.
gbmap.known matching disk is what required a separate
lookahead.bmapped in the first place, but we never use both fields.
- _Don't_ revert gbmap on failed mdir commits!
This was broken! If we reverted we risked inheriting outdated
in-flight block information.
This could be fixed by also zeroing lookahead.bmapped, but would force
a gbmap rebuild. And why? The only interaction between mdir commit and
the gbmap is block allocation, which is intentionally allowed to go
out-of-sync to relax issues like this.
Note we still revert in lfs3_fs_grow, the new gbmap we create there is
incompatible with the previous disk size.
As a part of these changes, gbmap.window now behaves roughly the same as
gbmap.known and updates eagerly on block allocation.
This makes lookahead.window and gbmap.window somewhat redundant, but
simplifies the relevant logic (especially due to how lookahead.window
lags behind lookahead.off).
---
A bunch of bugs fell out-of-this, the interactions with lfs3_fs_mkgbmap
and lfs3_fs_grow being especially tricky, but fortunately our testing is
doing a good job.
At least the code changes were minimal, saves a bit of RAM:
code stack ctx
no-gbmap before: 37168 2352 684
no-gbmap after: 37168 (+0.0%) 2352 (+0.0%) 684 (+0.0%)
code stack ctx
maybe-gbmap before: 39688 2392 852
maybe-gbmap after: 39720 (+0.1%) 2376 (-0.7%) 848 (-0.5%)
code stack ctx
yes-gbmap before: 39156 2392 852
yes-gbmap after: 39208 (+0.1%) 2376 (-0.7%) 848 (-0.5%)
|
||
|
Christopher Haster
|
b5a94f3397 |
gbmap: Added mkgbmap and rmgbmap for enabling/disabling the gbmap
These two functions allow changing whether or not the gbmap is in use
after format:
// Enable the global on-disk block-map
//
// Returns a negative error code on failure. Does nothing if a gbmap
// already exists.
int lfs3_fs_mkgbmap(lfs3_t *lfs3);
// Disable the global on-disk block-map
//
// Returns a negative error code on failure. Does nothing if no gbmap
// is found.
int lfs3_fs_rmgbmap(lfs3_t *lfs3);
rmgbmap was easy enough, but implementing mkgbmap turned out to be
surprisingly tricky due to how gstate permeates the system:
- Even if we zero gstate when we removing the gbmap, mounting the
image on a driver that doesn't understand the gbmap results in garbage
gstate over time as mdir compacts drop unknown gdeltas.
I think this sort of implicit gdelta cleanup is a good thing, but the
possibility of garbage gstate is a bit annoying.
Example A: the dbg scripts are currently printing a bunch of warnings
for corrupt gstate that can be safely ignored.
To support recovering from garbage gstate in mkgbmap, I changed
lfs3_fs_commitgdelta to _always_ track p state even when disabled. We
already needed to do this in lfs3_fs_flush/consumegdelta anyways,
since we don't know if the gbmap is used until parsing wcompat flags.
- The commit that enables the gbmap is tricky. We need the gbmap enabled
to calculate the new gdelta, but we also need it disabled so we don't
traverse the existing gbmap_p (which may be garbage).
As a workaround I added gbmap.b_p, which is in theory redundant with
gbmap_p, but (1) avoids needing to decode gbmap_p during traversals,
and (2) allows the two to temporarily fall out-of-sync in mkgbmap.
This means we potentially have 5 (!) snaphots flying around when
rebuilding the gbmap, which is starting to get a bit silly. But this
was also motivated by gbmap_p decoding adding roughly the same amount
of RAM to lfs3_mtree_traverse_, so the total RAM usage should in
theory be roughly the same.
There might be a better solution, but this at least gets mkgbmap
working. The gbmap builds are not our most RAM senstive configurations
anyways.
---
Also added a couple more tests in test_gbmap to test these:
- test_gbmap_files
- test_gbmap_rmgbmap
- test_gbmap_mkgbmap
- test_gbmap_rmmkgbmap
- test_gbmap_mkrmgbmap
And an explicit wraparound test to test_alloc. This was loosely implied
by the nospc tests, but it's probably better to have an explicit test.
The only downside is this implementation is limited to files:
- test_alloc_wraparound_files
---
Note we are currently dealing with three different configurations:
no-gbmap (the default), yes-gbmap (LFS3_YES_GBMAP), and maybe-gbmap
(LFS3_GBMAP + LFS3_F_GBMAP at runtime).
It only makes sense to include these in maybe-gbmap mode, so this is the
only mode with a notable code increase. However these functions are
relatively cheap. The stack/ctx changes also affect yes-gbmap, but
should mostly cancel out, see above:
code stack ctx
no-gbmap before: 37168 2352 684
no-gbmap after: 37168 (+0.0%) 2352 (+0.0%) 684 (+0.0%)
code stack ctx
maybe-gbmap before: 39292 2456 800
maybe-gbmap after: 39688 (+1.0%) 2392 (-2.6%) 852 (+6.5%)
code stack ctx
yes-gbmap before: 39116 2456 800
yes-gbmap after: 39156 (+0.1%) 2392 (-2.6%) 852 (+6.5%)
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Christopher Haster
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cb9bda5a94 |
gbmap: Renamed gbmap_scan_thresh -> gbmap_rebuild_thresh
I think a good rule of thumb is if you refer to some variable/config/ field with a different name in comments/writing/etc more often than not, you should just rename the variable/config/field to match. So yeah, gbmap_rebuild_thresh controls when the gbmap is rebuilt. Also touched up the doc comment a bit. |
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Christopher Haster
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ea05ad04b9 |
gbmap: Cleanup of gbmap comments, TODOs, code formatting, etc
Just cleaning up a bunch of outdated TODOs and commented out code, as well as a little bit of code formatting, and scrubbing airspace/gbatc names as these are no longer used and will just confuse new users. |