From fca1223ccfac2a461d7d3e29fb09a1b2142bdd7f Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Thu, 3 Dec 2020 14:17:33 -0500 Subject: [PATCH] bcachefs: Avoid write lock on mark_lock mark_lock is a frequently taken lock, and there's also potential for deadlocks since currently bch2_clear_page_bits which is called from memory reclaim has to take it to drop disk reservations. The disk reservation get path takes it when it recalculates the number of sectors known to be available, but it's not really needed for consistency. We just want to make sure we only have one thread updating the sectors_available count, which we can do with a dedicated mutex. Signed-off-by: Kent Overstreet --- fs/bcachefs/bcachefs.h | 1 + fs/bcachefs/buckets.c | 16 +++++----------- fs/bcachefs/super.c | 2 ++ 3 files changed, 8 insertions(+), 11 deletions(-) diff --git a/fs/bcachefs/bcachefs.h b/fs/bcachefs/bcachefs.h index 807291c33f5c0..877ce788d4135 100644 --- a/fs/bcachefs/bcachefs.h +++ b/fs/bcachefs/bcachefs.h @@ -640,6 +640,7 @@ struct bch_fs { unsigned bucket_size_max; atomic64_t sectors_available; + struct mutex sectors_available_lock; struct bch_fs_pcpu __percpu *pcpu; diff --git a/fs/bcachefs/buckets.c b/fs/bcachefs/buckets.c index ff4c61371830a..2488a2227bd9b 100644 --- a/fs/bcachefs/buckets.c +++ b/fs/bcachefs/buckets.c @@ -1182,13 +1182,6 @@ void bch2_trans_fs_usage_apply(struct btree_trans *trans, /* Disk reservations: */ -static u64 bch2_recalc_sectors_available(struct bch_fs *c) -{ - percpu_u64_set(&c->pcpu->sectors_available, 0); - - return avail_factor(__bch2_fs_usage_read_short(c).free); -} - void __bch2_disk_reservation_put(struct bch_fs *c, struct disk_reservation *res) { percpu_down_read(&c->mark_lock); @@ -1222,7 +1215,6 @@ int bch2_disk_reservation_add(struct bch_fs *c, struct disk_reservation *res, if (get < sectors) { preempt_enable(); - percpu_up_read(&c->mark_lock); goto recalculate; } } while ((v = atomic64_cmpxchg(&c->sectors_available, @@ -1240,9 +1232,10 @@ out: return 0; recalculate: - percpu_down_write(&c->mark_lock); + mutex_lock(&c->sectors_available_lock); - sectors_available = bch2_recalc_sectors_available(c); + percpu_u64_set(&c->pcpu->sectors_available, 0); + sectors_available = avail_factor(__bch2_fs_usage_read_short(c).free); if (sectors <= sectors_available || (flags & BCH_DISK_RESERVATION_NOFAIL)) { @@ -1256,7 +1249,8 @@ recalculate: ret = -ENOSPC; } - percpu_up_write(&c->mark_lock); + mutex_unlock(&c->sectors_available_lock); + percpu_up_read(&c->mark_lock); return ret; } diff --git a/fs/bcachefs/super.c b/fs/bcachefs/super.c index e0d4898ad0f54..b954a4e47e157 100644 --- a/fs/bcachefs/super.c +++ b/fs/bcachefs/super.c @@ -669,6 +669,8 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts) bch2_fs_btree_cache_init_early(&c->btree_cache); + mutex_init(&c->sectors_available_lock); + if (percpu_init_rwsem(&c->mark_lock)) goto err; -- 2.30.2