From mboxrd@z Thu Jan 1 00:00:00 1970 From: brookxu Subject: [PATCH 1/2] mem_cgroup: optimize the atomic count of wb_completion Date: Fri, 24 Sep 2021 14:46:22 +0800 Message-ID: <1632465983-30525-1-git-send-email-brookxu.cn@gmail.com> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id; bh=H3OrsFf3LDF8kSA9N72sHEwF/fijXJFJCQiPZi5ceNI=; b=G5C/0K7kIPn/uiaKVOaxliCn+ouk/2e/osVmj23SnCpR85VvwHouKbfuHaBSy+boIb NrLyylleC0PA3Lue5lGpx20aF/ecY5JzRgsujH9BvrKqT4te1OHXzpPJZ9i3onCiy4CL P3v/TRdjiy3NOnOGjTVCdu41amLOzx6RPNRP+8ZtPsgZ+TNPy6XL3YQc5n6mDBAIWbQX Q2+K4iqYoXamQjcW2JSVR9CscB+QuxHR2BheEYgKHm8ImCecNHgWDH9uYNaPwbbDpkMI V1BRTrN/Vy08LtJ58RWLyMgw9w3gXQymyllFJ9ffvuIof7yQjH2eKxZ+6a8rwo/kXmR/ xpnw== List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org From: Chunguang Xu In order to track inflight foreign writeback, we init wb_completion.cnt to 1. For normal writeback, this cause wb_wait_for_completion() to perform meaningless atomic operations. Since foreign writebacks rarely occur in most scenarios, we can init wb_completion.cnt to 0 and set frn.done.cnt to 1. In this way we can avoid unnecessary atomic operations. Signed-off-by: Chunguang Xu --- fs/fs-writeback.c | 1 - include/linux/backing-dev-defs.h | 2 +- mm/memcontrol.c | 7 ++++--- 3 files changed, 5 insertions(+), 5 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 81ec192..1ef10f2 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -186,7 +186,6 @@ static void wb_queue_work(struct bdi_writeback *wb, */ void wb_wait_for_completion(struct wb_completion *done) { - atomic_dec(&done->cnt); /* put down the initial count */ wait_event(*done->waitq, !atomic_read(&done->cnt)); } diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h index 3320700..38bd571 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -71,7 +71,7 @@ struct wb_completion { }; #define __WB_COMPLETION_INIT(_waitq) \ - (struct wb_completion){ .cnt = ATOMIC_INIT(1), .waitq = (_waitq) } + (struct wb_completion){ .cnt = ATOMIC_INIT(0), .waitq = (_waitq) } /* * If one wants to wait for one or more wb_writeback_works, each work's diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b762215..3e1384a6 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5168,9 +5168,10 @@ static struct mem_cgroup *mem_cgroup_alloc(void) #endif #ifdef CONFIG_CGROUP_WRITEBACK INIT_LIST_HEAD(&memcg->cgwb_list); - for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) - memcg->cgwb_frn[i].done = - __WB_COMPLETION_INIT(&memcg_cgwb_frn_waitq); + for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) { + atomic_set(&memcg->cgwb_frn[i].done.cnt, 1); + memcg->cgwb_frn[i].done.waitq = &memcg_cgwb_frn_waitq; + } #endif #ifdef CONFIG_TRANSPARENT_HUGEPAGE spin_lock_init(&memcg->deferred_split_queue.split_queue_lock); -- 1.8.3.1