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=-24.8 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL 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 96094C433E0 for ; Tue, 22 Dec 2020 03:49:28 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id F297422CB2 for ; Tue, 22 Dec 2020 03:49:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F297422CB2 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0BAA88D0009; Mon, 21 Dec 2020 22:49:27 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 06C338D0001; Mon, 21 Dec 2020 22:49:27 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EC31B8D0009; Mon, 21 Dec 2020 22:49:26 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0223.hostedemail.com [216.40.44.223]) by kanga.kvack.org (Postfix) with ESMTP id D5F348D0001 for ; Mon, 21 Dec 2020 22:49:26 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 81A8E1EE6 for ; Tue, 22 Dec 2020 03:49:26 +0000 (UTC) X-FDA: 77619538332.12.band95_2309e9c2745c Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id 5733718019D34 for ; Tue, 22 Dec 2020 03:49:26 +0000 (UTC) X-HE-Tag: band95_2309e9c2745c X-Filterd-Recvd-Size: 5198 Received: from mail-oo1-f47.google.com (mail-oo1-f47.google.com [209.85.161.47]) by imf18.hostedemail.com (Postfix) with ESMTP for ; Tue, 22 Dec 2020 03:49:25 +0000 (UTC) Received: by mail-oo1-f47.google.com with SMTP id n127so2677065ooa.13 for ; Mon, 21 Dec 2020 19:49:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=tdbzTUr3Pw+6/KahxCTYW+sU0lmWimxwgvACiw9JQC4=; b=Ah+5ws13d8qEq+zKY2YxfDFxNB/pkPb8TPI5D2Jb66/8ljWGfpt0/vBhscSxCYIM3M pHDyJ18A3QaQg0ysMehXTMPrEPkryCt3HGYUSG0ege4TWudhwtvz+JUm9GolsgQgu/A7 gO5Yb20kiNXJ71NQi+yBYFyi4RzGS0WrPBTjgQIkFERQsPU5a59rJDM6bBWUU5O2UUHO IpmOj54GadwxljRncz62G+D5rL+B4Ui5xiryTJpnATsEGpobjt0TYOKNB3jsDBeM08du U7mz8wiFxtNkTYo7HDY+czagkcsfiG+fX3bynidHNLj1Fw01a4tjlqefZYMp5EFRnB6Y vLtQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version; bh=tdbzTUr3Pw+6/KahxCTYW+sU0lmWimxwgvACiw9JQC4=; b=m1PPEUSZKWlHNAF6aCYMEupbkLgDyzPxI8jLUbRx491J99k/JUsF1O7pGJBgQC168e 0IPQj5PYhn87/IxmCYFzZNdVgVbxVZ8ev4INUaNTuels5dcPqOO0ea8+M/5tKOLxL3xH W+8Yh+yLU7uh3oTwaWtLILT9m7IUJs5M32+MUnpqPM78PHLrU5Vf0HyUPQZBv6bmeYit WPF/Xw7m7oeyCAkz2WqHcfmrjhE1wPMiKQUJmClW73P36hhLP4rvryUpylqW1+4VIUu9 X5BklhxE440JOt5kVQD0QeaT9W9mE7IKGEizqjY6FjJbFitzp/CDi+3Fnicqa5PjOEsq k2xA== X-Gm-Message-State: AOAM532i7LstibWEnq9q13/2/SFkVHyJw8xFXsMluUcBKsGDOeT75EWz CJqmLxygTQriMeZQszEpXHj3dw== X-Google-Smtp-Source: ABdhPJwdjDX3efR2YEyq+TOjs89PsUEP3xUtG0V2ICwD/6hUdtnXmt0XxvdnSpjuj2qQHDS//g0BoA== X-Received: by 2002:a4a:81:: with SMTP id 123mr13729306ooh.46.1608608964904; Mon, 21 Dec 2020 19:49:24 -0800 (PST) Received: from eggly.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id r25sm4312600otp.23.2020.12.21.19.49.23 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Mon, 21 Dec 2020 19:49:24 -0800 (PST) Date: Mon, 21 Dec 2020 19:49:22 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Alex Shi cc: Andrew Morton , Hugh Dickins , Johannes Weiner , Alexander Duyck , Hui Su , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] mm/compaction: remove rcu_read_lock during page compaction In-Reply-To: <1608186532-81218-3-git-send-email-alex.shi@linux.alibaba.com> Message-ID: References: <1608186532-81218-1-git-send-email-alex.shi@linux.alibaba.com> <1608186532-81218-3-git-send-email-alex.shi@linux.alibaba.com> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII 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: On Thu, 17 Dec 2020, Alex Shi wrote: > rcu_read_lock was used to guard memcg destory, now TestClearPageLRU > could block this happen, so we don't need it. Remove it to reduce > locking load in debugging mode. " isolate_migratepages_block() used rcu_read_lock() with the intention of safeguarding against the mem_cgroup being destroyed concurrently; but its TestClearPageLRU already protects against that. Delete the unnecessary rcu_read_lock() and _unlock(). " > > Signed-off-by: Alex Shi > Cc: Hugh Dickins Acked-by: Hugh Dickins > Cc: Johannes Weiner > Cc: Andrew Morton > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > --- > mm/compaction.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 8049d3530812..02af220fb992 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -995,7 +995,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > if (!TestClearPageLRU(page)) > goto isolate_fail_put; > > - rcu_read_lock(); > lruvec = mem_cgroup_page_lruvec(page, pgdat); > > /* If we already hold the lock, we can skip some rechecking */ > @@ -1005,7 +1004,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > > compact_lock_irqsave(&lruvec->lru_lock, &flags, cc); > locked = lruvec; > - rcu_read_unlock(); > > lruvec_memcg_debug(lruvec, page); > > @@ -1026,8 +1024,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > SetPageLRU(page); > goto isolate_fail_put; > } > - } else > - rcu_read_unlock(); > + } > > /* The whole page is taken off the LRU; skip the tail pages. */ > if (PageCompound(page)) > -- > 2.29.GIT