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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 EA476C33CB2 for ; Wed, 15 Jan 2020 01:19:24 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B9007214AF for ; Wed, 15 Jan 2020 01:19:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B9007214AF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 520048E0005; Tue, 14 Jan 2020 20:19:24 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4D0998E0003; Tue, 14 Jan 2020 20:19:24 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 40EB08E0005; Tue, 14 Jan 2020 20:19:24 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0106.hostedemail.com [216.40.44.106]) by kanga.kvack.org (Postfix) with ESMTP id 2C91F8E0003 for ; Tue, 14 Jan 2020 20:19:24 -0500 (EST) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id CB963283D for ; Wed, 15 Jan 2020 01:19:23 +0000 (UTC) X-FDA: 76378110606.15.owner59_17c436e60d321 X-HE-Tag: owner59_17c436e60d321 X-Filterd-Recvd-Size: 3423 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Wed, 15 Jan 2020 01:19:23 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Jan 2020 17:19:21 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,320,1574150400"; d="scan'208";a="225799881" Received: from unknown (HELO localhost) ([10.239.159.54]) by orsmga006.jf.intel.com with ESMTP; 14 Jan 2020 17:19:18 -0800 Date: Wed, 15 Jan 2020 09:19:27 +0800 From: Wei Yang To: David Rientjes Cc: "Kirill A. Shutemov" , Michal Hocko , Wei Yang , hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kirill.shutemov@linux.intel.com, yang.shi@linux.alibaba.com, alexander.duyck@gmail.com Subject: Re: [Patch v2] mm: thp: grab the lock before manipulation defer list Message-ID: <20200115011927.GB4916@richard> Reply-To: Wei Yang References: <20200109143054.13203-1-richardw.yang@linux.intel.com> <20200111000352.efy6krudecpshezh@box> <20200114093122.GH19428@dhcp22.suse.cz> <20200114103112.o6ozdbkfnzdsc2ke@box> <20200114105921.eo2vdwikrvtt3gkb@box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) 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 Tue, Jan 14, 2020 at 12:57:22PM -0800, David Rientjes wrote: >On Tue, 14 Jan 2020, Kirill A. Shutemov wrote: > >> split_huge_page_to_list() has page lock taken. >> >> free_transhuge_page() is in the free path and doesn't susceptible to the >> race. >> >> deferred_split_scan() is trickier. list_move() should be safe against >> list_empty() as it will not produce false-positive list_empty(). >> list_del_init() *should* (correct me if I'm wrong) be safe because the page >> is freeing and memcg will not touch the page anymore. >> >> deferred_split_huge_page() is a problematic one. It called from >> page_remove_rmap() path witch does require page lock. I don't see any >> obvious way to exclude race with mem_cgroup_move_account() here. >> Anybody else? >> >> Wei, could you rewrite the commit message with deferred_split_huge_page() >> as a race source instead of split_huge_page_to_list()? >> > >I think describing the race in terms of deferred_split_huge_page() makes >the most sense and I'd prefer a cc to stable for 5.4+. Even getting the >split_queue_len, which is unsigned long, to underflow because of a >list_empty(page_deferred_list()) check that is no longer accurate after >the lock is taken would be a significant issue for shrinkers. Oh, you are right. Even the list is not corrupted between deferred_split_scan() and mem_cgroup_move_account(), split_queue_len would be in a wrong state. Hmm... to some extend, the page lock complicates the picture a little here, even it helps in some cases. -- Wei Yang Help you, Help me