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bcachefs: Ensure proper write alignment

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There was a buggy version of bcachefs-tools which picked misaligned
bucket sizes when formatting, and we're also about to do dynamic block
sizes - which will allow picking logical block size or physical block
size of the device per-write, allowing for better compression ratios at
the cost of slightly worse write performance (i.e. forcing the device to
do RMW or extra buffering).

To account for this, tweak bch2_alloc_sectors_start() to properly align
open_buckets to the blocksize of the write we're about to do.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2025-05-04 16:31:40 -04:00
parent 844f766e02
commit 50a7b899a0
1 changed files with 21 additions and 1 deletions
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22
fs/bcachefs/alloc_foreground.c
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@ -1422,11 +1422,31 @@ int bch2_alloc_sectors_start_trans(struct btree_trans *trans,
wp->sectors_free = UINT_MAX;
open_bucket_for_each(c, &wp->ptrs, ob, i)
open_bucket_for_each(c, &wp->ptrs, ob, i) {
/*
* Ensure proper write alignment - either due to misaligned
* bucket sizes (from buggy bcachefs-tools), or writes that mix
* logical/physical alignment:
*/
struct bch_dev *ca = ob_dev(c, ob);
u64 offset = bucket_to_sector(ca, ob->bucket) +
ca->mi.bucket_size -
ob->sectors_free;
unsigned align = round_up(offset, block_sectors(c)) - offset;
ob->sectors_free = max_t(int, 0, ob->sectors_free - align);
wp->sectors_free = min(wp->sectors_free, ob->sectors_free);
}
wp->sectors_free = rounddown(wp->sectors_free, block_sectors(c));
/* Did alignment use up space in an open_bucket? */
if (unlikely(!wp->sectors_free)) {
bch2_alloc_sectors_done(c, wp);
goto retry;
}
BUG_ON(!wp->sectors_free || wp->sectors_free == UINT_MAX);
return 0;