A recent bug report uncovered a scenario where a filesystem never runs with freespace_initialized, and therefore the user observes significantly degraded write performance by virtue of running the early bucket allocator. The associated bug aside, the primary cause of the performance drop in this particular instance is that the early bucket allocator does not update the allocation cursor. This means that every allocation walks the alloc btree from the first bucket of the associated device looking for a bucket marked as free space.
Update the early allocator code to set the alloc cursor to the prospectively allocated bucket, similar to how the freelist allocator behaves. This improves performance of the early bucket allocator dramatically (even though it should be bypassed in favor of the freelist allocator in most cases). Signed-off-by: Brian Foster <[email protected]> --- cshepherd on #bcache originally reported the early bucket allocator problem and helped chase it down to what looks like a members_v2 regression. I believe he was planning to post a patch for that one. Brian fs/bcachefs/alloc_foreground.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/bcachefs/alloc_foreground.c b/fs/bcachefs/alloc_foreground.c index 3bc4abd3d7d5..be3fc0f38c79 100644 --- a/fs/bcachefs/alloc_foreground.c +++ b/fs/bcachefs/alloc_foreground.c @@ -431,7 +431,7 @@ bch2_bucket_alloc_early(struct btree_trans *trans, } bch2_trans_iter_exit(trans, &iter); - ca->alloc_cursor = alloc_cursor; + ca->alloc_cursor = IS_ERR_OR_NULL(ob) ? alloc_cursor : ob->bucket; if (!ob && ret) ob = ERR_PTR(ret); -- 2.41.0
