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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A6798C3F68F for ; Sun, 19 Jan 2020 02:24:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8825A24699 for ; Sun, 19 Jan 2020 02:24:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728748AbgASCYt (ORCPT ); Sat, 18 Jan 2020 21:24:49 -0500 Received: from mga07.intel.com ([134.134.136.100]:50568 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727403AbgASCYt (ORCPT ); Sat, 18 Jan 2020 21:24:49 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Jan 2020 18:24:48 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,336,1574150400"; d="scan'208";a="219305781" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga008.jf.intel.com with ESMTP; 18 Jan 2020 18:24:45 -0800 Date: Sun, 19 Jan 2020 10:24:56 +0800 From: Wei Yang To: David Rientjes Cc: Andrew Morton , Wei Yang , hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, ktkhai@virtuozzo.com, kirill.shutemov@linux.intel.com, yang.shi@linux.alibaba.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, alexander.duyck@gmail.com, stable@vger.kernel.org Subject: Re: [Patch v4] mm: thp: remove the defer list related code since this will not happen Message-ID: <20200119022456.GC9745@richard> Reply-To: Wei Yang References: <20200117233836.3434-1-richardw.yang@linux.intel.com> <20200118145421.0ab96d5d9bea21a3339d52fe@linux-foundation.org> 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 Sat, Jan 18, 2020 at 03:36:06PM -0800, David Rientjes wrote: >On Sat, 18 Jan 2020, Andrew Morton wrote: > >> On Sat, 18 Jan 2020 07:38:36 +0800 Wei Yang wrote: >> >> > If compound is true, this means it is a PMD mapped THP. Which implies >> > the page is not linked to any defer list. So the first code chunk will >> > not be executed. >> > >> > Also with this reason, it would not be proper to add this page to a >> > defer list. So the second code chunk is not correct. >> > >> > Based on this, we should remove the defer list related code. >> > >> > Fixes: 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg aware") >> > >> > Signed-off-by: Wei Yang >> > Suggested-by: Kirill A. Shutemov >> > Cc: [5.4+] >> >> This patch is identical to "mm: thp: grab the lock before manipulating >> defer list", which is rather confusing. Please let people know when >> this sort of thing is done. >> >> The earlier changelog mentioned a possible race condition. This >> changelog does not. In fact this changelog fails to provide any >> description of any userspace-visible runtime effects of the bug. >> Please send along such a description for inclusion, as always. >> > >The locking concern that Wei was originally looking at is no longer an >issue because we determined that the code in question could simply be >removed. > >I think the following can be added to the changelog: > >----->o----- > >When migrating memcg charges of thp memory, there are two possibilities: > > (1) The underlying compound page is mapped by a pmd and thus does is not > on a deferred split queue (it's mapped), or > > (2) The compound page is not mapped by a pmd and is awaiting split on a > deferred split queue. > >The current charge migration implementation does *not* migrate charges for >thp memory on the deferred split queue, it only migrates charges for pages >that are mapped by a pmd. > >Thus, to migrate charges, the underlying compound page cannot be on a >deferred split queue; no list manipulation needs to be done in >mem_cgroup_move_account(). > >With the current code, the underlying compound page is moved to the >deferred split queue of the memcg its memory is not charged to, so >susbequent reclaim will consider these pages for the wrong memcg. Remove >the deferred split queue handling in mem_cgroup_move_account() entirely. > >----->o----- > >Acked-by: David Rientjes Hi David, The changlog looks awesome to me. Thanks ~ Hi Andrew I see you queue this in you tree, do I need to rewrite a patch with better changelog? -- Wei Yang Help you, Help me