Commit 50a7b899 authored by Kent Overstreet's avatar Kent Overstreet
Browse files

bcachefs: Ensure proper write alignment 



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: default avatarKent Overstreet <kent.overstreet@linux.dev>
parent 844f766e

fs/bcachefs/alloc_foreground.c

+21 −1
Original line number Diff line number Diff line
@@ -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;