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 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 6978DC433DB for ; Tue, 9 Mar 2021 00:10:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 33FEC652A8 for ; Tue, 9 Mar 2021 00:10:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231939AbhCIAK0 (ORCPT ); Mon, 8 Mar 2021 19:10:26 -0500 Received: from mail.kernel.org ([198.145.29.99]:44738 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229471AbhCIAKL (ORCPT ); Mon, 8 Mar 2021 19:10:11 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8F2DA61554; Tue, 9 Mar 2021 00:10:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1615248610; bh=G+XxYbDAZEkn2FIZ+ZBvU40zQIFN6Avf7NxiFSYEp+A=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=cPGCohWHaDmvGP+xRZcMObUGnPY8ZJoLv2uLCDc6nKdz6svpz8QkZJQ3dCWFZ6u3m KGe9rrv+60owkCDCYKYR20N18wfksSbR2QEfIIcSCEHP0LFIi8O23dBhdeLtuHWQqy 9Fe2cX7n5o2MdY3XBYVkwW2cRKxJotHsPvXaIzUY= Date: Mon, 8 Mar 2021 16:10:08 -0800 From: Andrew Morton To: Matthew Wilcox Cc: Michal Hocko , 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: <20210308161008.a5d17c56551bf59b778c1d75@linux-foundation.org> In-Reply-To: <20210308204731.GE3479805@casper.infradead.org> References: <20210304074053.65527-1-zhouguanghui1@huawei.com> <20210304074053.65527-3-zhouguanghui1@huawei.com> <20210305155840.4bb6dea4fb473d9ffbe49c99@linux-foundation.org> <20210308124227.f9b343f006d26ba8d47a959c@linux-foundation.org> <20210308204731.GE3479805@casper.infradead.org> 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 Mon, 8 Mar 2021 20:47:31 +0000 Matthew Wilcox wrote: > On Mon, Mar 08, 2021 at 12:42:27PM -0800, Andrew Morton wrote: > > On Mon, 8 Mar 2021 09:41:38 +0100 Michal Hocko wrote: > > > > > On Fri 05-03-21 15:58:40, Andrew Morton wrote: > > > > 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? > > > > > > Somebody more familiar with iommu dma allocation layer should have a > > > look as well (__iommu_dma_alloc_pages) so that we know whether there are > > > kernels outside of the above two ones mentioned above that need a fix. > > > But in general this sounds like a good fit for the stable tree. > > > > OK. I reversed the order of these two patches so we don't need to > > burden -stable with a cosmetic rename. > > Eek, no. > > The alloc_pages_exact() is done to pages that _aren't_ compound. > So you have to pass the number of pages to the memcg split function, > because a non-compound page doesn't know the size of its allocation. Ah, OK, the patch title fooled me. It should have been a three-patch series, really 1: add nr_pages arg to mem_cgroup_split_huge_fixup() 2: call mem_cgroup_split_huge_fixup() when splitting 3: rename mem_cgroup_split_huge_fixup() to split_page_memcg() That way, the third cosmetic patch could be deferred so we don't feed the cosmetic renaming into -stable. But whatever, the rename isn't a big deal so I'll go with the 2-patch series as sent for -stable.