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 84463C33C9E for ; Wed, 15 Jan 2020 01:19:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 61AA9214AF for ; Wed, 15 Jan 2020 01:19:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728897AbgAOBTX (ORCPT ); Tue, 14 Jan 2020 20:19:23 -0500 Received: from mga05.intel.com ([192.55.52.43]:6900 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728824AbgAOBTX (ORCPT ); Tue, 14 Jan 2020 20:19:23 -0500 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 fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Jan 2020 17:19:22 -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) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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