From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D636C433EF for ; Fri, 24 Sep 2021 06:46:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2530F61214 for ; Fri, 24 Sep 2021 06:46:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244261AbhIXGsA (ORCPT ); Fri, 24 Sep 2021 02:48:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44136 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244211AbhIXGr7 (ORCPT ); Fri, 24 Sep 2021 02:47:59 -0400 Received: from mail-pg1-x52c.google.com (mail-pg1-x52c.google.com [IPv6:2607:f8b0:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BA235C061574; Thu, 23 Sep 2021 23:46:26 -0700 (PDT) Received: by mail-pg1-x52c.google.com with SMTP id m21so8919642pgu.13; Thu, 23 Sep 2021 23:46:26 -0700 (PDT) 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== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=H3OrsFf3LDF8kSA9N72sHEwF/fijXJFJCQiPZi5ceNI=; b=xThpVOzvnJn6CwJrKY6UUFACPj556DXSpzVRGJ2rybeT2o+ocCbgUgg/PNb1Nnz94V N6zoT9vTY9+UVKP/DyR7ygyzysmLc2J4PwG0cpvigrPxSIbd/wXZeDQ4iod61MOa+rJU dnl6mUHTIIQk+hxJPui3bdwmWu54jwjFiTf9MvAzCl5nh+ClTl2OJFs5JL60pyBnBvIP T8VFjC6KgwWSkof8rFcDq04Nlb35sG9xcC2NrnSDNCFBNVKvcBSersArP5ArQ8csjwwA iMAixrTU5IGhCEJte1Jr4NCFEbn7N//Kl1GXAjdVRDdBb8gwi7EVgzmn3CTrJN6uW7wI 7b0Q== X-Gm-Message-State: AOAM533gz5BAcuLK+PtZ733zODry7Y5HC8RUy3bnItX2K9CyucIj4R/7 +lG43OBjAnPRf9vF+yPDz/8= X-Google-Smtp-Source: ABdhPJwlOV2dYDrKjWgQc4v6KA8VJC7pFS3+WF10ir4vYU21T1tvKetc/uxk/HdNl64mig1aoLhoSg== X-Received: by 2002:a63:f5b:: with SMTP id 27mr2386085pgp.302.1632465986239; Thu, 23 Sep 2021 23:46:26 -0700 (PDT) Received: from VM-0-3-centos.localdomain ([101.32.213.191]) by smtp.gmail.com with ESMTPSA id q20sm7978818pfc.57.2021.09.23.23.46.24 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 Sep 2021 23:46:25 -0700 (PDT) From: brookxu To: hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org 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> X-Mailer: git-send-email 1.8.3.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.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