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[60.242.181.102]) by smtp.gmail.com with ESMTPSA id u27sm678055pfg.83.2021.08.01.20.20.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 01 Aug 2021 20:20:24 -0700 (PDT) From: Nicholas Piggin To: Andrew Morton Cc: Nicholas Piggin , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Anton Blanchard Subject: [PATCH v1] fs/epoll: use a per-cpu counter for user's watches count Date: Mon, 2 Aug 2021 13:20:13 +1000 Message-Id: <20210802032013.2751916-1-npiggin@gmail.com> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This counter tracks the number of watches a user has, to compare against the 'max_user_watches' limit. This causes a scalability bottleneck on SPECjbb2015 on large systems as there is only one user. Changing to a per-cpu counter increases throughput of the benchmark by about 30% on a 16-socket, > 1000 thread system. Reported-by: Anton Blanchard Signed-off-by: Nicholas Piggin --- fs/eventpoll.c | 18 ++++++++++-------- include/linux/sched/user.h | 3 ++- kernel/user.c | 9 +++++++++ 3 files changed, 21 insertions(+), 9 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 1e596e1d0bba..648ed77f4164 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -723,7 +723,7 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi) */ call_rcu(&epi->rcu, epi_rcu_free); - atomic_long_dec(&ep->user->epoll_watches); + percpu_counter_dec(&ep->user->epoll_watches); return 0; } @@ -1439,7 +1439,6 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, { int error, pwake = 0; __poll_t revents; - long user_watches; struct epitem *epi; struct ep_pqueue epq; struct eventpoll *tep = NULL; @@ -1449,11 +1448,15 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, lockdep_assert_irqs_enabled(); - user_watches = atomic_long_read(&ep->user->epoll_watches); - if (unlikely(user_watches >= max_user_watches)) + if (unlikely(percpu_counter_compare(&ep->user->epoll_watches, + max_user_watches) >= 0)) return -ENOSPC; - if (!(epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL))) + percpu_counter_inc(&ep->user->epoll_watches); + + if (!(epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL))) { + percpu_counter_dec(&ep->user->epoll_watches); return -ENOMEM; + } /* Item initialization follow here ... */ INIT_LIST_HEAD(&epi->rdllink); @@ -1466,17 +1469,16 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, mutex_lock_nested(&tep->mtx, 1); /* Add the current item to the list of active epoll hook for this file */ if (unlikely(attach_epitem(tfile, epi) < 0)) { - kmem_cache_free(epi_cache, epi); if (tep) mutex_unlock(&tep->mtx); + kmem_cache_free(epi_cache, epi); + percpu_counter_dec(&ep->user->epoll_watches); return -ENOMEM; } if (full_check && !tep) list_file(tfile); - atomic_long_inc(&ep->user->epoll_watches); - /* * Add the current item to the RB tree. All RB tree operations are * protected by "mtx", and ep_insert() is called with "mtx" held. diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h index 2462f7d07695..00ed419dd464 100644 --- a/include/linux/sched/user.h +++ b/include/linux/sched/user.h @@ -4,6 +4,7 @@ #include #include +#include #include #include @@ -13,7 +14,7 @@ struct user_struct { refcount_t __count; /* reference count */ #ifdef CONFIG_EPOLL - atomic_long_t epoll_watches; /* The number of file descriptors currently watched */ + struct percpu_counter epoll_watches; /* The number of file descriptors currently watched */ #endif unsigned long unix_inflight; /* How many files in flight in unix sockets */ atomic_long_t pipe_bufs; /* how many pages are allocated in pipe buffers */ diff --git a/kernel/user.c b/kernel/user.c index c82399c1618a..a2673f940506 100644 --- a/kernel/user.c +++ b/kernel/user.c @@ -138,6 +138,7 @@ static void free_user(struct user_struct *up, unsigned long flags) { uid_hash_remove(up); spin_unlock_irqrestore(&uidhash_lock, flags); + percpu_counter_destroy(&up->epoll_watches); kmem_cache_free(uid_cachep, up); } @@ -185,6 +186,10 @@ struct user_struct *alloc_uid(kuid_t uid) new->uid = uid; refcount_set(&new->__count, 1); + if (percpu_counter_init(&new->epoll_watches, 0, GFP_KERNEL)) { + kmem_cache_free(uid_cachep, new); + return NULL; + } ratelimit_state_init(&new->ratelimit, HZ, 100); ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE); @@ -195,6 +200,7 @@ struct user_struct *alloc_uid(kuid_t uid) spin_lock_irq(&uidhash_lock); up = uid_hash_find(uid, hashent); if (up) { + percpu_counter_destroy(&new->epoll_watches); kmem_cache_free(uid_cachep, new); } else { uid_hash_insert(new, hashent); @@ -216,6 +222,9 @@ static int __init uid_cache_init(void) for(n = 0; n < UIDHASH_SZ; ++n) INIT_HLIST_HEAD(uidhash_table + n); + if (percpu_counter_init(&root_user.epoll_watches, 0, GFP_KERNEL)) + panic("percpu cpunter alloc failed"); + /* Insert the root user immediately (init already runs as root) */ spin_lock_irq(&uidhash_lock); uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID)); -- 2.23.0