From 8f7f566f5774d36196bfa87bc097522fd497d4dc Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Fri, 17 Jun 2022 01:07:54 -0400 Subject: [PATCH] bcachefs: btree key cache pcpu freedlist Originally, the btree key cache code would always allocate new entries by reusing from the recently-freed list, if that list wasn't empty. But that behaviour was dropped, for lock contention reasons. But it seems that entries stranded on the freed list have been contributing to some of our oom issues, because long running btree transactions will prevent them from being freed. This patch re-adds allocating from the freed list, but it also adds percpu buffers to solve the lock contention issues - and the new percpu freed lists will improve the evict paths, too. Signed-off-by: Kent Overstreet --- fs/bcachefs/btree_key_cache.c | 121 ++++++++++++++++++++++++++++------ fs/bcachefs/btree_types.h | 8 ++- 2 files changed, 108 insertions(+), 21 deletions(-) diff --git a/fs/bcachefs/btree_key_cache.c b/fs/bcachefs/btree_key_cache.c index bc0c8386e4034..97c72f3917eca 100644 --- a/fs/bcachefs/btree_key_cache.c +++ b/fs/bcachefs/btree_key_cache.c @@ -84,7 +84,7 @@ static void bkey_cached_free(struct btree_key_cache *bc, start_poll_synchronize_srcu(&c->btree_trans_barrier); list_move_tail(&ck->list, &bc->freed); - bc->nr_freed++; + atomic_long_inc(&bc->nr_freed); kfree(ck->k); ck->k = NULL; @@ -94,10 +94,88 @@ static void bkey_cached_free(struct btree_key_cache *bc, six_unlock_intent(&ck->c.lock); } +static void bkey_cached_free_fast(struct btree_key_cache *bc, + struct bkey_cached *ck) +{ + struct bch_fs *c = container_of(bc, struct bch_fs, btree_key_cache); + struct btree_key_cache_freelist *f; + bool freed = false; + + BUG_ON(test_bit(BKEY_CACHED_DIRTY, &ck->flags)); + + ck->btree_trans_barrier_seq = + start_poll_synchronize_srcu(&c->btree_trans_barrier); + + list_del_init(&ck->list); + atomic_long_inc(&bc->nr_freed); + + kfree(ck->k); + ck->k = NULL; + ck->u64s = 0; + + preempt_disable(); + f = this_cpu_ptr(bc->pcpu_freed); + + if (f->nr < ARRAY_SIZE(f->objs)) { + f->objs[f->nr++] = ck; + freed = true; + } + preempt_enable(); + + if (!freed) { + mutex_lock(&bc->lock); + preempt_disable(); + f = this_cpu_ptr(bc->pcpu_freed); + + while (f->nr > ARRAY_SIZE(f->objs) / 2) { + struct bkey_cached *ck2 = f->objs[--f->nr]; + + list_move_tail(&ck2->list, &bc->freed); + } + preempt_enable(); + + list_move_tail(&ck->list, &bc->freed); + mutex_unlock(&bc->lock); + } + + six_unlock_write(&ck->c.lock); + six_unlock_intent(&ck->c.lock); +} + static struct bkey_cached * bkey_cached_alloc(struct btree_key_cache *c) { - struct bkey_cached *ck; + struct bkey_cached *ck = NULL; + struct btree_key_cache_freelist *f; + + preempt_disable(); + f = this_cpu_ptr(c->pcpu_freed); + if (f->nr) + ck = f->objs[--f->nr]; + preempt_enable(); + + if (!ck) { + mutex_lock(&c->lock); + preempt_disable(); + f = this_cpu_ptr(c->pcpu_freed); + + while (!list_empty(&c->freed) && + f->nr < ARRAY_SIZE(f->objs) / 2) { + ck = list_last_entry(&c->freed, struct bkey_cached, list); + list_del_init(&ck->list); + f->objs[f->nr++] = ck; + } + + ck = f->nr ? f->objs[--f->nr] : NULL; + preempt_enable(); + mutex_unlock(&c->lock); + } + + if (ck) { + six_lock_intent(&ck->c.lock, NULL, NULL); + six_lock_write(&ck->c.lock, NULL, NULL); + return ck; + } ck = kmem_cache_alloc(bch2_key_cache, GFP_NOFS|__GFP_ZERO); if (likely(ck)) { @@ -120,16 +198,6 @@ bkey_cached_reuse(struct btree_key_cache *c) struct bkey_cached *ck; unsigned i; - mutex_lock(&c->lock); - list_for_each_entry_reverse(ck, &c->freed, list) - if (bkey_cached_lock_for_evict(ck)) { - c->nr_freed--; - list_del(&ck->list); - mutex_unlock(&c->lock); - return ck; - } - mutex_unlock(&c->lock); - rcu_read_lock(); tbl = rht_dereference_rcu(c->table.tbl, &c->table); for (i = 0; i < tbl->size; i++) @@ -190,9 +258,7 @@ btree_key_cache_create(struct bch_fs *c, six_unlock_intent(&ck->c.lock); kfree(ck); } else { - mutex_lock(&bc->lock); - bkey_cached_free(bc, ck); - mutex_unlock(&bc->lock); + bkey_cached_free_fast(bc, ck); } return NULL; @@ -465,9 +531,7 @@ evict: bkey_cached_evict(&c->btree_key_cache, ck); - mutex_lock(&c->btree_key_cache.lock); - bkey_cached_free(&c->btree_key_cache, ck); - mutex_unlock(&c->btree_key_cache.lock); + bkey_cached_free_fast(&c->btree_key_cache, ck); } out: bch2_trans_iter_exit(trans, &b_iter); @@ -612,7 +676,7 @@ static unsigned long bch2_btree_key_cache_scan(struct shrinker *shrink, list_del(&ck->list); kmem_cache_free(bch2_key_cache, ck); - bc->nr_freed--; + atomic_long_dec(&bc->nr_freed); scanned++; freed++; } @@ -685,6 +749,7 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc) struct bkey_cached *ck, *n; struct rhash_head *pos; unsigned i; + int cpu; if (bc->shrink.list.next) unregister_shrinker(&bc->shrink); @@ -701,6 +766,16 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc) } rcu_read_unlock(); + for_each_possible_cpu(cpu) { + struct btree_key_cache_freelist *f = + per_cpu_ptr(bc->pcpu_freed, cpu); + + for (i = 0; i < f->nr; i++) { + ck = f->objs[i]; + list_add(&ck->list, &bc->freed); + } + } + list_for_each_entry_safe(ck, n, &bc->freed, list) { cond_resched(); @@ -721,6 +796,8 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc) if (bc->table_init_done) rhashtable_destroy(&bc->table); + + free_percpu(bc->pcpu_freed); } void bch2_fs_btree_key_cache_init_early(struct btree_key_cache *c) @@ -734,6 +811,10 @@ int bch2_fs_btree_key_cache_init(struct btree_key_cache *bc) struct bch_fs *c = container_of(bc, struct bch_fs, btree_key_cache); int ret; + bc->pcpu_freed = alloc_percpu(struct btree_key_cache_freelist); + if (!bc->pcpu_freed) + return -ENOMEM; + ret = rhashtable_init(&bc->table, &bch2_btree_key_cache_params); if (ret) return ret; @@ -748,7 +829,7 @@ int bch2_fs_btree_key_cache_init(struct btree_key_cache *bc) void bch2_btree_key_cache_to_text(struct printbuf *out, struct btree_key_cache *c) { - prt_printf(out, "nr_freed:\t%zu\n", c->nr_freed); + prt_printf(out, "nr_freed:\t%zu\n", atomic_long_read(&c->nr_freed)); prt_printf(out, "nr_keys:\t%lu\n", atomic_long_read(&c->nr_keys)); prt_printf(out, "nr_dirty:\t%lu\n", atomic_long_read(&c->nr_dirty)); } diff --git a/fs/bcachefs/btree_types.h b/fs/bcachefs/btree_types.h index 4f3e1086a86b3..2eb8cc11aec40 100644 --- a/fs/bcachefs/btree_types.h +++ b/fs/bcachefs/btree_types.h @@ -298,6 +298,11 @@ struct btree_iter { struct bpos journal_pos; }; +struct btree_key_cache_freelist { + struct bkey_cached *objs[16]; + unsigned nr; +}; + struct btree_key_cache { struct mutex lock; struct rhashtable table; @@ -305,8 +310,9 @@ struct btree_key_cache { struct list_head freed; struct shrinker shrink; unsigned shrink_iter; + struct btree_key_cache_freelist __percpu *pcpu_freed; - size_t nr_freed; + atomic_long_t nr_freed; atomic_long_t nr_keys; atomic_long_t nr_dirty; }; -- 2.30.2