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gc: Enabled committing the gbmap if we have nothing else to do

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This kinda fell out of the preerase gc work.

Normally, we're lazy about committing the gbmap into the mtree. Most
on-demand gbmap rebuilds are followed by an mdir commit anyways, so
normally it would just add redundant work and muddy up the
lfs3_alloc_ckpoint path.

But this isn't the case for gc work, which will probably be followed by
long periods of idling. If we lose power while idling (which, let's be
honest, is the most likely time to lose power), we'll lose any
gbmap-related gc progres. Not ideal.

Fortunately, avoiding this is easy. We just need an additional step
after any traversal/preerasing gc work that eagerly commits the gbmap
into the mtree.

The only downside is a bit more code:

                    code          stack          ctx
  before:          35116           2136          660
  after:           35116 (+0.0%)   2136 (+0.0%)  660 (+0.0%)

                    code          stack          ctx
  gbmap+np before: 38188           2144          776
  gbmap+np after:  38252 (+0.2%)   2144 (+0.0%)  776 (+0.0%)

                    code          stack          ctx
  gbmap+yp before: 38608           2144          796
  gbmap+yp after:  38664 (+0.1%)   2144 (+0.0%)  796 (+0.0%)
This commit is contained in:
Christopher Haster
2025-12-08 15:32:56 -06:00
parent 843412cc79
commit be69c9912f
1 changed files with 12 additions and 5 deletions
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lfs3.c
+12 -5
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@@ -16633,11 +16633,18 @@ static int lfs3_fs_gc_(lfs3_t *lfs3, lfs3_mgc_t *mgc,
}
#endif
// TODO do this
// // if we have nothing else to do, try to commit the gbmap to
// // disk so it's recoverable if we lose power
// } else if (lfs3_btree_cmp(&lfs3->gbmap.b, &lfs3->gbmap.b_p) != 0) {
// // TODO
// if we have nothing else to do, try to commit the gbmap to
// disk so it's recoverable if we lose power
} else if (LFS3_IFDEF_GBMAP(
lfs3_btree_cmp(&lfs3->gbmap.b, &lfs3->gbmap.b_p) != 0,
false)) {
#if !defined(LFS3_RDONLY) && defined(LFS3_GBMAP)
int err = lfs3_mdir_commit(lfs3, &lfs3->mroot,
LFS3_RATTRS(LFS3_RATTR_NULL));
if (err) {
return err;
}
#endif
// nothing to do at all? guess we're done
} else {