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Increase threshold for superblock expansion from ~50% -> ~88% full

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Superblock expansion is an irreversible operation. In an effort to
prevent superblock expansion from claiming valuable scratch space
(important for small, <~8 block filesystems), littlefs prevents
superblock expansion when the disk is "mostly full".

In true computer-scientist fashion, this "mostly full" threshold was
set to ~50%.

As pointed out by gbolgradov and rojer, >~50% utilization is not
uncommon, and it can lead to a situation where superblock expansion does
not occur in a relatively healthy filesystem, causing focused wear at
the root.

To remedy this, the threshold is now increased to ~88% (7/8) full.

This may change in the future and should probably be eventually user
configurable.

Found by gbolgradov and rojer
This commit is contained in:
Christopher Haster
2023-12-19 16:35:09 -06:00
parent c733d9ec57
commit b9b95ab4bc
1 changed files with 5 additions and 3 deletions
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lfs.c
+5 -3
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@@ -2151,9 +2151,11 @@ static int lfs_dir_splittingcompact(lfs_t *lfs, lfs_mdir_t *dir,
return size; return size;
} }
// do we have extra space? littlefs can't reclaim this space // littlefs cannot reclaim expanded superblocks, so expand cautiously
// by itself, so expand cautiously //
if ((lfs_size_t)size < lfs->block_count/2) { // if our filesystem is more than ~88% full, don't expand, this is
// somewhat arbitrary
if (lfs->block_count - size > lfs->block_count/8) {
LFS_DEBUG("Expanding superblock at rev %"PRIu32, dir->rev); LFS_DEBUG("Expanding superblock at rev %"PRIu32, dir->rev);
int err = lfs_dir_split(lfs, dir, attrs, attrcount, int err = lfs_dir_split(lfs, dir, attrs, attrcount,
source, begin, end); source, begin, end);