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t: Reverted reverted most of LFS_T_MKCONSISTENT

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After thinking about this for a bit, there are some compelling
motivations for including an incremental LFS_T_MKCONSISTENT:

- Being able to run incremental LFS_T_MKCONSISTENT traversals in
  parallel with read-only operations is actually quite enticing.

  The only complicated part is maintaining the invalidatable traversal
  state, which already exists with lfsr_traversal_t (except the
  annoying LFS_F_MUTATED bit).

- While it's not really effective to combine LFS_T_MKCONSISTENT and
  LFS_T_LOOKAHEAD traversals, it _is_ possible to combine
  LFS_T_MKCONSISTENT with LFS_T_COMPACT, LFS_T_CKMETA,
  LFS_T_REPAIRMETA (future), etc.

  Really, LFS_T_LOOKAHEAD is the odd one out.

- Making LFS_T_MKCONSISTENT incremental means all filesystem-level
  traversals (except lfsr_mount) can be run incrementally. Which is a
  nice feature to have when O(n = entire fs) risks being very long
  running.

The main downside of LFS_T_MKCONSISTENT (and LFS_T_COMPACT, etc) is that
attempting to run it immediately after mount will likely recursively
trigger a lookahead scan to satisfy block allocation requests -- which
will block the current thread for the duration of the lookahead scan.
But this seems to be more a problem of LFS_T_LOOKAHEAD interacting with
other traversals poorly.

Fortunately, long term, the current plan is to replace the lookahead
buffer with an on-disk block map on disks where the lookahead scan is a
bottleneck. If this gets implemented the problem goes away.

So re-reverting this for now. Worst case we can always re-re-revert this
again in the future. There is already a working implementation, so might
as well see where it goes...

Supporting incremental LFS_T_MKCONSISTENT does add a bit of a code
cost, but there is still some room for deduplicating lfsr_mtree_gc +
lfsr_fs_mkconsistent, which may be interesting:

           code          stack
  before: 35232           2680
  after:  35480 (+0.7%)   2680 (+0.0%)
This commit is contained in:
Christopher Haster
2024-07-08 23:04:04 -05:00
parent ffe8c1e820
commit 0e2a909148
3 changed files with 140 additions and 50 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lfs.c
+128 -45
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@@ -8265,6 +8265,10 @@ static inline bool lfsr_f_isdirty(uint32_t flags) {
return flags & LFS_F_DIRTY;
}
static inline bool lfsr_f_ismutated(uint32_t flags) {
return flags & LFS_F_MUTATED;
}
// needed in lfsr_mtree_traverse_
@@ -8648,6 +8652,7 @@ static int lfsr_mtree_gc(lfs_t *lfs, lfsr_traversal_t *t,
// lfsr_mtree_gc to work correctly
LFS_ASSERT(lfsr_omdir_isopen(lfs, &t->o.o));
again:;
lfsr_tag_t tag;
lfsr_bptr_t bptr;
int err = lfsr_mtree_traverse(lfs, t,
@@ -8656,6 +8661,32 @@ static int lfsr_mtree_gc(lfs_t *lfs, lfsr_traversal_t *t,
return err;
}
// keep track of dirty flag before mutation
bool dirty = t->o.o.flags & LFS_F_DIRTY;
// mkconsistencing mdirs?
if (lfsr_t_ismkconsistent(t->o.o.flags)
&& tag == LFSR_TAG_MDIR
&& lfs->hasorphans) {
lfsr_mdir_t *mdir = (lfsr_mdir_t*)bptr.data.u.buffer;
int err = lfsr_mdir_fixorphans(lfs, mdir);
if (err) {
return err;
}
// did this drop our mdir?
if (mdir->mid != -1 && mdir->rbyd.weight == 0) {
t->o.o.flags &= ~LFS_F_ZOMBIE;
t->o.o.state = LFSR_TSTATE_MDIRS;
// downgrade any new dirty flags
t->o.o.flags |= (t->o.o.flags & LFS_F_DIRTY) ? LFS_F_MUTATED : 0;
t->o.o.flags &= ~LFS_F_DIRTY;
t->o.o.flags |= (dirty) ? LFS_F_DIRTY : 0;
goto again;
}
}
// compacting mdirs?
if (lfsr_t_iscompact(t->o.o.flags)
&& tag == LFSR_TAG_MDIR
@@ -8757,6 +8788,11 @@ static int lfsr_mtree_gc(lfs_t *lfs, lfsr_traversal_t *t,
t->u.bt.rid = t->u.bt.bid;
}
// downgrade any new dirty flags
t->o.o.flags |= (t->o.o.flags & LFS_F_DIRTY) ? LFS_F_MUTATED : 0;
t->o.o.flags &= ~LFS_F_DIRTY;
t->o.o.flags |= (dirty) ? LFS_F_DIRTY : 0;
if (tag_) {
*tag_ = tag;
}
@@ -12664,54 +12700,77 @@ static int lfsr_fs_fixgrm(lfs_t *lfs) {
return 0;
}
static int lfsr_mdir_fixorphans(lfs_t *lfs, lfsr_mdir_t *mdir) {
// save the current mid
lfsr_mid_t mid = mdir->mid;
// iterate through mids looking for orphans
mdir->mid = LFSR_MID(lfs, mdir->mid, 0);
int err;
while (lfsr_mid_rid(lfs, mdir->mid) < (lfsr_srid_t)mdir->rbyd.weight) {
// is this mid open? well we're not an orphan then, skip
if (lfsr_omdir_ismidopen(lfs, mdir->mid)) {
mdir->mid += 1;
continue;
}
// is this mid marked as an orphan?
err = lfsr_mdir_lookup(lfs, mdir, LFSR_TAG_ORPHAN,
NULL);
if (err) {
if (err == LFS_ERR_NOENT) {
mdir->mid += 1;
continue;
}
goto failed;
}
// we found an orphaned file, remove
LFS_DEBUG("Fixing orphan %"PRId32".%"PRId32,
lfsr_mid_bid(lfs, mdir->mid) >> lfs->mdir_bits,
lfsr_mid_rid(lfs, mdir->mid));
err = lfsr_mdir_commit(lfs, mdir, LFSR_ATTRS(
LFSR_ATTR(LFSR_TAG_RM, -1, LFSR_DATA_NULL())));
if (err) {
goto failed;
}
}
// restore the current mid
mdir->mid = mid;
return 0;
failed:;
// restore the current mid
mdir->mid = mid;
return err;
}
static int lfsr_fs_fixorphans(lfs_t *lfs) {
// iterate through the filesystem and remove any orphaned files
//
// note this never takes longer than lfsr_mount
//
lfsr_mdir_t mdir = {.mid=0};
while (mdir.mid < (lfsr_srid_t)lfsr_mtree_weight(lfs)) {
int err = lfsr_mtree_lookup(lfs, LFSR_MID(lfs, mdir.mid, 0),
lfsr_mid_t mid = 0;
while (mid < lfsr_mtree_weight(lfs)) {
lfsr_mdir_t mdir;
int err = lfsr_mtree_lookup(lfs, mid,
&mdir);
if (err) {
LFS_ASSERT(err != LFS_ERR_NOENT);
return err;
}
while (lfsr_mid_rid(lfs, mdir.mid)
< (lfsr_srid_t)mdir.rbyd.weight) {
// is this mid open? well we're not an orphan then, skip
if (lfsr_omdir_ismidopen(lfs, mdir.mid)) {
mdir.mid += 1;
continue;
}
// is this mid marked as an orphan?
err = lfsr_mdir_lookup(lfs, &mdir, LFSR_TAG_ORPHAN,
NULL);
if (err) {
if (err == LFS_ERR_NOENT) {
mdir.mid += 1;
continue;
}
return err;
}
// we found an orphaned file, remove
LFS_DEBUG("Fixing orphan %"PRId32".%"PRId32,
lfsr_mid_bid(lfs, mdir.mid) >> lfs->mdir_bits,
lfsr_mid_rid(lfs, mdir.mid));
err = lfsr_mdir_commit(lfs, &mdir, LFSR_ATTRS(
LFSR_ATTR(LFSR_TAG_RM, -1, LFSR_DATA_NULL())));
if (err) {
return err;
}
// clean up orphans
err = lfsr_mdir_fixorphans(lfs, &mdir);
if (err) {
return err;
}
// increment mid unless we dropped the mdir
// incremend mid unless we dropped the mdir
if (mdir.rbyd.weight > 0) {
mdir.mid = lfsr_mid_bid(lfs, mdir.mid) + 1;
mid += 1 << lfs->mdir_bits;
}
}
@@ -12856,14 +12915,34 @@ int lfsr_traversal_read(lfs_t *lfs, lfsr_traversal_t *t,
struct lfs_tinfo *tinfo) {
LFS_ASSERT(lfsr_omdir_isopen(lfs, &t->o.o));
// mkconsistencing?
//
// check every step in case some other operation introduced a grm/orphan
if (lfsr_t_ismkconsistent(t->o.o.flags)) {
int err = lfsr_fs_mkconsistent(lfs);
// check for pending grms every step, just in case some other
// operation introduced new grms
if (lfsr_t_ismkconsistent(t->o.o.flags)
&& lfsr_grm_count(lfs) > 0) {
if (lfsr_grm_count(lfs) == 2) {
LFS_DEBUG("Fixing grm %"PRId32".%"PRId32" %"PRId32".%"PRId32,
lfsr_mid_bid(lfs, lfs->grm.mids[0]) >> lfs->mdir_bits,
lfsr_mid_rid(lfs, lfs->grm.mids[0]),
lfsr_mid_bid(lfs, lfs->grm.mids[1]) >> lfs->mdir_bits,
lfsr_mid_rid(lfs, lfs->grm.mids[1]));
} else if (lfsr_grm_count(lfs) == 1) {
LFS_DEBUG("Fixing grm %"PRId32".%"PRId32,
lfsr_mid_bid(lfs, lfs->grm.mids[0]) >> lfs->mdir_bits,
lfsr_mid_rid(lfs, lfs->grm.mids[0]));
}
// keep track of dirty flag before mutation
bool dirty = t->o.o.flags & LFS_F_DIRTY;
int err = lfsr_fs_fixgrm(lfs);
if (err) {
return err;
}
// downgrade any new dirty flags
t->o.o.flags |= (t->o.o.flags & LFS_F_DIRTY) ? LFS_F_MUTATED : 0;
t->o.o.flags &= ~LFS_F_DIRTY;
t->o.o.flags |= (dirty) ? LFS_F_DIRTY : 0;
}
while (true) {
@@ -12915,9 +12994,16 @@ int lfsr_traversal_read(lfs_t *lfs, lfsr_traversal_t *t,
}
done:;
// was mkconsistent successful?
if (lfsr_t_ismkconsistent(t->o.o.flags)
&& !lfsr_f_isdirty(t->o.o.flags)) {
lfs->hasorphans = false;
}
// was a lookahead scan successful?
if (lfsr_t_islookahead(t->o.o.flags)
&& !lfsr_f_isdirty(t->o.o.flags)) {
&& !lfsr_f_isdirty(t->o.o.flags)
&& !lfsr_f_ismutated(t->o.o.flags)) {
lfs_alloc_markfree(lfs);
}
@@ -12926,11 +13012,8 @@ done:;
static void lfsr_traversal_clobber(lfs_t *lfs, lfsr_traversal_t *t) {
(void)lfs;
// not yet started?
if (t->o.o.state < LFSR_TSTATE_MROOTCHAIN) {
// do nothing
// mroot/mtree? transition to mdir iteration
} else if (t->o.o.state < LFSR_TSTATE_MDIRS) {
if (t->o.o.state < LFSR_TSTATE_MDIRS) {
t->o.o.state = LFSR_TSTATE_MDIRS;
t->o.o.mdir.mid = 0;
t->o.bshrub.u.bshrub.weight = 0;
@@ -12963,7 +13046,7 @@ static void lfsr_traversal_clobber(lfs_t *lfs, lfsr_traversal_t *t) {
static int lfsr_traversal_rewind_(lfs_t *lfs, lfsr_traversal_t *t) {
(void)lfs;
// reset traversal
t->o.o.flags &= ~LFS_F_DIRTY;
t->o.o.flags &= ~LFS_F_DIRTY & ~LFS_F_MUTATED;
t->o.o.state = LFSR_TSTATE_MROOTANCHOR;
t->o.o.mdir.mid = -1;
t->o.o.mdir.rbyd.weight = 0;