From 94ace3fec8477f8a46d08fc57cd1dd5efbd0a32b Mon Sep 17 00:00:00 2001 From: Chengming Zhou Date: Fri, 16 Feb 2024 08:55:05 +0000 Subject: mm/zswap: change zswap_pool kref to percpu_ref All zswap entries will take a reference of zswap_pool when zswap_store(), and drop it when free. Change it to use the percpu_ref is better for scalability performance. Although percpu_ref use a bit more memory which should be ok for our use case, since we almost have only one zswap_pool to be using. The performance gain is for zswap_store/load hotpath. Testing kernel build (32 threads) in tmpfs with memory.max=2GB. (zswap shrinker and writeback enabled with one 50GB swapfile, on a 128 CPUs x86-64 machine, below is the average of 5 runs) mm-unstable zswap-global-lru real 63.20 63.12 user 1061.75 1062.95 sys 268.74 264.44 [chengming.zhou@linux.dev: fix zswap_pools_lock usages after changing to percpu_ref] Link: https://lkml.kernel.org/r/20240228154954.3028626-1-chengming.zhou@linux.dev Link: https://lkml.kernel.org/r/20240210-zswap-global-lru-v3-2-200495333595@bytedance.com Signed-off-by: Chengming Zhou Reviewed-by: Nhat Pham Cc: Johannes Weiner Cc: Yosry Ahmed Cc: Chengming Zhou Signed-off-by: Andrew Morton --- mm/zswap.c | 48 +++++++++++++++++++++++++++++++++--------------- 1 file changed, 33 insertions(+), 15 deletions(-) (limited to 'mm/zswap.c') diff --git a/mm/zswap.c b/mm/zswap.c index 0141c45a5a6f..da90933c6d20 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -173,7 +173,7 @@ struct crypto_acomp_ctx { struct zswap_pool { struct zpool *zpools[ZSWAP_NR_ZPOOLS]; struct crypto_acomp_ctx __percpu *acomp_ctx; - struct kref kref; + struct percpu_ref ref; struct list_head list; struct work_struct release_work; struct hlist_node node; @@ -305,6 +305,7 @@ static void zswap_update_total_size(void) /********************************* * pool functions **********************************/ +static void __zswap_pool_empty(struct percpu_ref *ref); static struct zswap_pool *zswap_pool_create(char *type, char *compressor) { @@ -358,13 +359,18 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) /* being the current pool takes 1 ref; this func expects the * caller to always add the new pool as the current pool */ - kref_init(&pool->kref); + ret = percpu_ref_init(&pool->ref, __zswap_pool_empty, + PERCPU_REF_ALLOW_REINIT, GFP_KERNEL); + if (ret) + goto ref_fail; INIT_LIST_HEAD(&pool->list); zswap_pool_debug("created", pool); return pool; +ref_fail: + cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node); error: if (pool->acomp_ctx) free_percpu(pool->acomp_ctx); @@ -437,8 +443,9 @@ static void __zswap_pool_release(struct work_struct *work) synchronize_rcu(); - /* nobody should have been able to get a kref... */ - WARN_ON(kref_get_unless_zero(&pool->kref)); + /* nobody should have been able to get a ref... */ + WARN_ON(!percpu_ref_is_zero(&pool->ref)); + percpu_ref_exit(&pool->ref); /* pool is now off zswap_pools list and has no references. */ zswap_pool_destroy(pool); @@ -446,13 +453,13 @@ static void __zswap_pool_release(struct work_struct *work) static struct zswap_pool *zswap_pool_current(void); -static void __zswap_pool_empty(struct kref *kref) +static void __zswap_pool_empty(struct percpu_ref *ref) { struct zswap_pool *pool; - pool = container_of(kref, typeof(*pool), kref); + pool = container_of(ref, typeof(*pool), ref); - spin_lock(&zswap_pools_lock); + spin_lock_bh(&zswap_pools_lock); WARN_ON(pool == zswap_pool_current()); @@ -461,7 +468,7 @@ static void __zswap_pool_empty(struct kref *kref) INIT_WORK(&pool->release_work, __zswap_pool_release); schedule_work(&pool->release_work); - spin_unlock(&zswap_pools_lock); + spin_unlock_bh(&zswap_pools_lock); } static int __must_check zswap_pool_get(struct zswap_pool *pool) @@ -469,12 +476,12 @@ static int __must_check zswap_pool_get(struct zswap_pool *pool) if (!pool) return 0; - return kref_get_unless_zero(&pool->kref); + return percpu_ref_tryget(&pool->ref); } static void zswap_pool_put(struct zswap_pool *pool) { - kref_put(&pool->kref, __zswap_pool_empty); + percpu_ref_put(&pool->ref); } static struct zswap_pool *__zswap_pool_current(void) @@ -591,7 +598,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, return -EINVAL; } - spin_lock(&zswap_pools_lock); + spin_lock_bh(&zswap_pools_lock); pool = zswap_pool_find_get(type, compressor); if (pool) { @@ -600,17 +607,28 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, list_del_rcu(&pool->list); } - spin_unlock(&zswap_pools_lock); + spin_unlock_bh(&zswap_pools_lock); if (!pool) pool = zswap_pool_create(type, compressor); + else { + /* + * Restore the initial ref dropped by percpu_ref_kill() + * when the pool was decommissioned and switch it again + * to percpu mode. + */ + percpu_ref_resurrect(&pool->ref); + + /* Drop the ref from zswap_pool_find_get(). */ + zswap_pool_put(pool); + } if (pool) ret = param_set_charp(s, kp); else ret = -EINVAL; - spin_lock(&zswap_pools_lock); + spin_lock_bh(&zswap_pools_lock); if (!ret) { put_pool = zswap_pool_current(); @@ -625,7 +643,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, put_pool = pool; } - spin_unlock(&zswap_pools_lock); + spin_unlock_bh(&zswap_pools_lock); if (!zswap_has_pool && !pool) { /* if initial pool creation failed, and this pool creation also @@ -642,7 +660,7 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, * or the new pool we failed to add */ if (put_pool) - zswap_pool_put(put_pool); + percpu_ref_kill(&put_pool->ref); return ret; } -- cgit v1.2.3