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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 50272C433DB for ; Fri, 5 Mar 2021 23:59:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1CAF7650AE for ; Fri, 5 Mar 2021 23:59:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229719AbhCEX7U (ORCPT ); Fri, 5 Mar 2021 18:59:20 -0500 Received: from mail.kernel.org ([198.145.29.99]:58332 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229592AbhCEX6l (ORCPT ); Fri, 5 Mar 2021 18:58:41 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id DF3DE601FE; Fri, 5 Mar 2021 23:58:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1614988721; bh=HbZT0bF1MsVnxN6BmosWjrgrZCSm028Kpqvom+zo5rA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=kP9fQL0oxzF4MeLAIlf9r2mjWb0IXmPVbfnY/LAipr6zyaplBjZKHIYvNDiD/vksT MxPzAQpWPcorsIEn0ivLCcIPgk2TU4tCLSY39d/t9fwKXPcwKtiMabmvhE/xlPzKwD Xlb3wWSDeMKoqkni3RpbOJg3TVMfltCCYWcH8+AU= Date: Fri, 5 Mar 2021 15:58:40 -0800 From: Andrew Morton To: Michal Hocko Cc: Zhou Guanghui , linux-kernel@vger.kernel.org, linux-mm@kvack.org, hannes@cmpxchg.org, hughd@google.com, kirill.shutemov@linux.intel.com, npiggin@gmail.com, ziy@nvidia.com, wangkefeng.wang@huawei.com, guohanjun@huawei.com, dingtianhong@huawei.com, chenweilong@huawei.com, rui.xiang@huawei.com Subject: Re: [PATCH v2 2/2] mm/memcg: set memcg when split page Message-Id: <20210305155840.4bb6dea4fb473d9ffbe49c99@linux-foundation.org> In-Reply-To: References: <20210304074053.65527-1-zhouguanghui1@huawei.com> <20210304074053.65527-3-zhouguanghui1@huawei.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 5 Mar 2021 12:52:52 +0100 Michal Hocko wrote: > On Thu 04-03-21 07:40:53, Zhou Guanghui wrote: > > As described in the split_page function comment, for the non-compound > > high order page, the sub-pages must be freed individually. If the > > memcg of the fisrt page is valid, the tail pages cannot be uncharged > > when be freed. > > > > For example, when alloc_pages_exact is used to allocate 1MB continuous > > physical memory, 2MB is charged(kmemcg is enabled and __GFP_ACCOUNT is > > set). When make_alloc_exact free the unused 1MB and free_pages_exact > > free the applied 1MB, actually, only 4KB(one page) is uncharged. > > > > Therefore, the memcg of the tail page needs to be set when split page. > > > > As already mentioned there are at least two explicit users of > __GFP_ACCOUNT with alloc_exact_pages added recently. It would be good to > mention that explicitly and maybe even mention 7efe8ef274024 resp. > c419621873713 so that it is clear this is not just a theoretical issue. I added : Michel: : : There are at least two explicit users of __GFP_ACCOUNT with : alloc_exact_pages added recently. See 7efe8ef274024 ("KVM: arm64: : Allocate stage-2 pgd pages with GFP_KERNEL_ACCOUNT") and c419621873713 : ("KVM: s390: Add memcg accounting to KVM allocations"), so this is not : just a theoretical issue. And should we cc:stable on this one?