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Adopted file->leaf, reworked how we track crystallization

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TLDR: Added file->leaf, which can track file fragments (read only) and
blocks independently from file->b.shrub. This speeds up linear
read/write performance at a heavy code/stack cost.

The jury is still out on if this ends up reverted.

---

This is another change motivated by benchmarking, specifically the
significant regression in linear reads.

The problem is that CTZ skip-lists are actually _really_ good at
appending blocks! (but only appending blocks) The entire state of the
file is contained in the last block, so file writes can resume without
any reads. With B-trees, we need at least 1 B-tree lookup to resume
appending, and this really adds up when writing extremely blocks.

To try to mitigate this, I added file->leaf, a single in-RAM bptr for
tracking the most recent leaf we've operated on. This avoids B-tree
lookups during linear reads, and allowing the leaf to fall out-of-sync
with the B-tree avoids both B-tree lookups and commits during writes.

Unfortunately this isn't a complete win for writes. If we write
fragments, i.e. cache_size < prog_size, we still need to incrementally
commit to the B-tree. Fragments are a bit annoying for caching as any
B-tree commit can discard the block they reside on.

For reading, however, this brings read performance back to roughly the
same as CTZ skip-lists.

---

This also turned into more-or-less a full rewrite of the lfsr_file_flush
-> lfsr_file_crystallize code path, which is probably a good thing. This
code needed some TLC.

file->leaf also replaces the previous eblock/eoff mechanism for
erased-state tracking via the new LFSR_BPTR_ISERASED flag. This should
be useful when exploring more erased-state tracking mechanisms (ddtree).

Unfortunately, all of this additional in-RAM state is very costly. I
think there's some cleanup that can be done (the current impl is a bit
of a mess/proof-of-concept), but this does add a significant chunk of
both code and stack:

           code          stack          ctx
  before: 36016           2296          636
  after:  37228 (+3.4%)   2328 (+1.4%)  636 (+0.0%)

file->leaf also increases the size of lfsr_file_t, but this doesn't show
up in ctx because struct lfs_info dominates:

  lfsr_file_t before: 116
  lfsr_file_t after:  136 (+17.2%)

Hm... Maybe ctx measurements should use a lower LFS_NAME_MAX?
This commit is contained in:
Christopher Haster
2025-05-21 00:21:10 -05:00
parent 2a1489a4da
commit 9ed326f3d3
6 changed files with 891 additions and 415 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tests/test_ck.toml
+14 -6
View File
@@ -3751,13 +3751,17 @@ code = '''
wbuf, SIZE);
assert(d == SIZE
|| d == LFS_ERR_NOSPC
|| (d == LFS_ERR_CORRUPT && (METHOD == 2 || METHOD == 3)));
|| (d == LFS_ERR_CORRUPT
&& (METHOD == 2 || METHOD == 3)));
if (d == LFS_ERR_NOSPC || d == LFS_ERR_CORRUPT) {
goto corrupt_mounted;
}
int err = lfsr_file_sync(&lfs, &sim_files[j]->file);
assert(err == 0 || err == LFS_ERR_NOSPC);
if (err == LFS_ERR_NOSPC) {
assert(err == 0
|| err == LFS_ERR_NOSPC
|| (err == LFS_ERR_CORRUPT
&& (METHOD == 2 || METHOD == 3)));
if (err == LFS_ERR_NOSPC || LFS_ERR_CORRUPT) {
goto corrupt_mounted;
}
@@ -4349,13 +4353,17 @@ code = '''
wbuf, SIZE);
assert(d == SIZE
|| d == LFS_ERR_NOSPC
|| (d == LFS_ERR_CORRUPT && (METHOD == 2 || METHOD == 3)));
|| (d == LFS_ERR_CORRUPT
&& (METHOD == 2 || METHOD == 3)));
if (d == LFS_ERR_NOSPC || d == LFS_ERR_CORRUPT) {
goto corrupt_mounted;
}
int err = lfsr_file_sync(&lfs, &sim_files[j]->file);
assert(err == 0 || err == LFS_ERR_NOSPC);
if (err == LFS_ERR_NOSPC) {
assert(err == 0
|| err == LFS_ERR_NOSPC
|| (err == LFS_ERR_CORRUPT
&& (METHOD == 2 || METHOD == 3)));
if (err == LFS_ERR_NOSPC || err == LFS_ERR_CORRUPT) {
goto corrupt_mounted;
}
tests/test_traversal.toml
+20
View File
@@ -2131,6 +2131,7 @@ code = '''
wbuf[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file, wbuf, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file) => 0;
if (SYNC) {
lfsr_file_sync(&lfs, &file) => 0;
}
@@ -2499,6 +2500,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
lfsr_file_t file2;
lfsr_file_open(&lfs, &file2, "tarantula",
@@ -2508,6 +2510,7 @@ code = '''
wbuf2[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file2, wbuf2, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file2) => 0;
// try traversing
lfsr_traversal_t t;
@@ -2531,6 +2534,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
// we should be at end of traversal now
lfsr_traversal_read(&lfs, &t, &tinfo) => LFS_ERR_NOENT;
@@ -2586,6 +2590,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
lfsr_file_t file2;
lfsr_file_open(&lfs, &file2, "tarantula",
@@ -2595,6 +2600,7 @@ code = '''
wbuf2[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file2, wbuf2, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file2) => 0;
// try traversing
lfsr_traversal_t t;
@@ -2624,6 +2630,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
// traverse btree
lfsr_traversal_read(&lfs, &t, &tinfo) => 0;
@@ -2686,6 +2693,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
lfsr_file_t file2;
lfsr_file_open(&lfs, &file2, "tarantula",
@@ -2695,6 +2703,7 @@ code = '''
wbuf2[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file2, wbuf2, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file2) => 0;
// try traversing
lfsr_traversal_t t;
@@ -2721,6 +2730,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
// traverse two data blocks
lfsr_traversal_read(&lfs, &t, &tinfo) => 0;
@@ -2781,6 +2791,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
lfsr_file_t file2;
lfsr_file_open(&lfs, &file2, "tarantula",
@@ -2790,6 +2801,7 @@ code = '''
wbuf2[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file2, wbuf2, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file2) => 0;
// try traversing
lfsr_traversal_t t;
@@ -2876,6 +2888,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
lfsr_file_t file2;
lfsr_file_open(&lfs, &file2, "tarantula",
@@ -2885,6 +2898,7 @@ code = '''
wbuf2[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file2, wbuf2, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file2) => 0;
// try traversing
lfsr_traversal_t t;
@@ -2984,6 +2998,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
lfsr_file_t file2;
lfsr_file_open(&lfs, &file2, "tarantula",
@@ -2993,6 +3008,7 @@ code = '''
wbuf2[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file2, wbuf2, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file2) => 0;
// try traversing
lfsr_traversal_t t;
@@ -6835,6 +6851,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
lfsr_file_t file2;
lfsr_file_open(&lfs, &file2, "octopus",
@@ -6844,6 +6861,7 @@ code = '''
wbuf2[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file2, wbuf2, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file2) => 0;
// create this many orphaned files
//
@@ -7163,6 +7181,7 @@ code = '''
wbuf1[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file1, wbuf1, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file1) => 0;
lfsr_file_t file2;
lfsr_file_open(&lfs, &file2, "octopus",
@@ -7172,6 +7191,7 @@ code = '''
wbuf2[j] = 'a' + (TEST_PRNG(&prng) % 26);
}
lfsr_file_write(&lfs, &file2, wbuf2, SIZE) => SIZE;
lfsr_file_flush(&lfs, &file2) => 0;
// create this many orphaned files
//