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Changed lfs_dir_alloc to maximize block cycles for new metadata pairs

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Previously we only bumped the revision count if an eviction would occur
immediately (and possibly corrupt littlefs). This works, but does risk
an unoptimal superblock size if an almost-exhausted superblock was
allocated during lfs_format.

As pointed out by tim-nordell-nimbelink, we can align the revision count
to maximize the number of block cycles without breaking the existing
requirements of increasing revision counts.

As an added benefit, littlefs's wear-leveling should behave more
consistently after this change.
This commit is contained in:
Christopher Haster
2020-11-28 22:46:11 -06:00
parent d04c1392c0
commit b8dcf10974
1 changed files with 5 additions and 5 deletions
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10
lfs.c
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@@ -1375,11 +1375,11 @@ static int lfs_dir_alloc(lfs_t *lfs, lfs_mdir_t *dir) {
return err;
}
// make sure we don't immediately evict, see lfs_dir_compact for why
// this check is so complicated
if (lfs->cfg->block_cycles > 0 &&
(dir->rev + 1) % ((lfs->cfg->block_cycles+1)|1) == 0) {
dir->rev += 1;
// to make sure we don't immediately evict, align the new revision count
// to our block_cycles modulus, see lfs_dir_compact for why our modulus
// is tweaked this way
if (lfs->cfg->block_cycles > 0) {
dir->rev = lfs_alignup(dir->rev, ((lfs->cfg->block_cycles+1)|1));
}
// set defaults