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From: Chengming Zhou Date: Fri, 16 Feb 2024 08:55:05 +0000 Subject: [PATCH v3 2/2] mm/zswap: change zswap_pool kref to percpu_ref Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20240210-zswap-global-lru-v3-2-200495333595@bytedance.com> References: <20240210-zswap-global-lru-v3-0-200495333595@bytedance.com> In-Reply-To: <20240210-zswap-global-lru-v3-0-200495333595@bytedance.com> To: Johannes Weiner , Yosry Ahmed , Nhat Pham , Andrew Morton Cc: linux-mm@kvack.org, Yosry Ahmed , linux-kernel@vger.kernel.org, Chengming Zhou X-Migadu-Flow: FLOW_OUT 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=3D2GB. (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 Signed-off-by: Chengming Zhou Reviewed-by: Nhat Pham --- mm/zswap.c | 36 +++++++++++++++++++++++++++--------- 1 file changed, 27 insertions(+), 9 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index d275eb523fc4..961349162997 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); =20 static struct zswap_pool *zswap_pool_create(char *type, char *compressor) { @@ -358,13 +359,18 @@ static struct zswap_pool *zswap_pool_create(char *typ= e, 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 =3D percpu_ref_init(&pool->ref, __zswap_pool_empty, + PERCPU_REF_ALLOW_REINIT, GFP_KERNEL); + if (ret) + goto ref_fail; INIT_LIST_HEAD(&pool->list); =20 zswap_pool_debug("created", pool); =20 return pool; =20 +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 *wo= rk) =20 synchronize_rcu(); =20 - /* 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); =20 /* pool is now off zswap_pools list and has no references. */ zswap_pool_destroy(pool); @@ -446,11 +453,11 @@ static void __zswap_pool_release(struct work_struct *= work) =20 static struct zswap_pool *zswap_pool_current(void); =20 -static void __zswap_pool_empty(struct kref *kref) +static void __zswap_pool_empty(struct percpu_ref *ref) { struct zswap_pool *pool; =20 - pool =3D container_of(kref, typeof(*pool), kref); + pool =3D container_of(ref, typeof(*pool), ref); =20 spin_lock(&zswap_pools_lock); =20 @@ -469,12 +476,12 @@ static int __must_check zswap_pool_get(struct zswap_p= ool *pool) if (!pool) return 0; =20 - return kref_get_unless_zero(&pool->kref); + return percpu_ref_tryget(&pool->ref); } =20 static void zswap_pool_put(struct zswap_pool *pool) { - kref_put(&pool->kref, __zswap_pool_empty); + percpu_ref_put(&pool->ref); } =20 static struct zswap_pool *__zswap_pool_current(void) @@ -604,6 +611,17 @@ static int __zswap_param_set(const char *val, const st= ruct kernel_param *kp, =20 if (!pool) pool =3D 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); + } =20 if (pool) ret =3D param_set_charp(s, kp); @@ -642,7 +660,7 @@ static int __zswap_param_set(const char *val, const str= uct 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); =20 return ret; } --=20 b4 0.10.1