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AJvYcCXGRJQn8rhDnjScfj+gWFq/9Rgo+coK23G4U1mQUYhpbexU2AE/whLiWxxaQDMcexI2x125psZtyyvEIAGSuGyoQIY= X-Gm-Message-State: AOJu0YwegIQ8ikcRZHRsTgGtAoyUuk6w02qlZ5YKvrMXzZHBBmw7ehKE kaOjYeB8aOjJuz+SRMc221a/AFGU0qRyejp8nuzskf37vfrE8Rdk9JBqBZGtvZX96EUaDjmhDYw dAmEIjJeszeVDM1uNxgci7voILY8= X-Google-Smtp-Source: AGHT+IEtO/VBcZaOfR4SFAmVXgxWcAixrZ9ZQ3VHLR/CaLimsilvIAh51ezi04vQ7iAabTcTPYI+c5WTYQ66/PSyLA4= X-Received: by 2002:a05:6602:1811:b0:7c3:fc2b:9bad with SMTP id t17-20020a056602181100b007c3fc2b9badmr6797908ioh.20.1707686487334; Sun, 11 Feb 2024 13:21:27 -0800 (PST) MIME-Version: 1.0 References: <20240210-zswap-global-lru-v1-0-853473d7b0da@bytedance.com> <20240210-zswap-global-lru-v1-2-853473d7b0da@bytedance.com> In-Reply-To: <20240210-zswap-global-lru-v1-2-853473d7b0da@bytedance.com> From: Nhat Pham Date: Sun, 11 Feb 2024 13:21:16 -0800 Message-ID: Subject: Re: [PATCH 2/2] mm/zswap: change zswap_pool kref to percpu_ref To: Chengming Zhou Cc: Andrew Morton , Johannes Weiner , Yosry Ahmed , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 3E31E4000A X-Stat-Signature: hqroeh951hmzxrw5nkageadajcjkwodr X-Rspam-User: X-HE-Tag: 1707686488-133261 X-HE-Meta: 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 DvggKsQH a1mZDmePsEqw/Bl1unZLd08UcgMZf4gEP2O4bv+6f4OHgcopbVfKzLXny/XhNssW7F+aoAcOaAasKDM4v1MCtcDm99mdMjtcQdFeI+k5/hf5uWmlItAaojGb+bHno3BMhAA4rTbPCPeRJtcwTvxVWCKk4PAjdgJFYrVASriKSQ5TEhvGEPCP8dUXGv/W5MwvR7IhJIa/1AZjI8nt4pTa+vEbO70wYfnoScwCJc2PPf3/r1RB7qumnPbzTvikz6VQHbAMDdNHN6KU11tPCDlW5G44nyfe/12MNXyqh0FPofzrB2/V3LgQmO6BpggjLBfTZAXXU8JRSaGPF6r66wLmx3WgiMfX+BqDg5SpbKugTC7BS/r0D8T7qBVTXI5pOJ/WoJwfiyU883NiSok/88d1wz+ajdfXFXMKpLb8mUwMS/CGbKiqSgHyoChSWGwXC2ikbh3ClybJDcq0jaUw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Feb 11, 2024 at 5:58=E2=80=AFAM Chengming Zhou wrote: > > 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. > > Testing kernel build in tmpfs with memory.max=3D2GB > (zswap shrinker and writeback enabled with one 50GB swapfile). > > 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 > --- > mm/zswap.c | 30 +++++++++++++++++++++--------- > 1 file changed, 21 insertions(+), 9 deletions(-) > > diff --git a/mm/zswap.c b/mm/zswap.c > index 7668db8c10e3..afb31904fb08 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; > @@ -303,6 +303,7 @@ 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= ) > { > @@ -356,13 +357,18 @@ static struct zswap_pool *zswap_pool_create(char *t= ype, 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); > > zswap_pool_debug("created", pool); > > return pool; > > +ref_fail: > + cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->no= de); > error: > if (pool->acomp_ctx) > free_percpu(pool->acomp_ctx); > @@ -435,8 +441,8 @@ 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)); Do we no longer care about this WARN? IIUC, this is to catch someone still holding a reference to the pool at release time, which sounds like a bug. I think we can simulate the similar behavior with: WARN_ON(percpu_ref_tryget(&pool->ref)) no? percpu_ref_tryget() should fail when the refcnt goes back down to 0. Then we can do percpu_ref_exit() as well. > + /* nobody should have been able to get a ref... */ > + percpu_ref_exit(&pool->ref); > > /* pool is now off zswap_pools list and has no references. */ > zswap_pool_destroy(pool); > @@ -444,11 +450,11 @@ 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 =3D container_of(kref, typeof(*pool), kref); > + pool =3D container_of(ref, typeof(*pool), ref); > > spin_lock(&zswap_pools_lock); > > @@ -467,12 +473,12 @@ 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) > @@ -602,6 +608,12 @@ static int __zswap_param_set(const char *val, const = struct kernel_param *kp, > > if (!pool) > pool =3D zswap_pool_create(type, compressor); > + else { > + /* Resurrect percpu_ref to percpu mode. */ > + percpu_ref_resurrect(&pool->ref); > + /* Drop the ref from zswap_pool_find_get(). */ > + zswap_pool_put(pool); > + } > > if (pool) > ret =3D param_set_charp(s, kp); > @@ -640,7 +652,7 @@ static int __zswap_param_set(const char *val, const s= truct 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; > } > > -- > b4 0.10.1 The rest of the code looks solid to me FWIW. Number seems to indicate this is a good idea as well.