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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 65D02C433DB for ; Tue, 9 Mar 2021 09:03:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 126A764F8E for ; Tue, 9 Mar 2021 09:03:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229652AbhCIJCe (ORCPT ); Tue, 9 Mar 2021 04:02:34 -0500 Received: from mx2.suse.de ([195.135.220.15]:50732 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229805AbhCIJCD (ORCPT ); Tue, 9 Mar 2021 04:02:03 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1615280522; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dce3cOdvnV2ClNKK9GPexH0rXQvpFnYmQS/x3knbop0=; b=TjE27we03nbMZ65GkVHR9bTmOSVDkiJqFD/+aoLCoYaYymNsPnJCbJS/NdDhMOwMYY1nCk iDQxQ7I4XMU+Q3EYPqWpmTb0z3Mqbk+G8OWHdvJukv/9ODODKAiwPqRXC5VAy8LyqV288E 9YF2IncWtI/zPuCdvoIR/NFHDELMzP8= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id CD201AC1F; Tue, 9 Mar 2021 09:02:01 +0000 (UTC) Date: Tue, 9 Mar 2021 10:02:00 +0100 From: Michal Hocko To: Matthew Wilcox Cc: Zhou Guanghui , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.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: References: <20210304074053.65527-1-zhouguanghui1@huawei.com> <20210304074053.65527-3-zhouguanghui1@huawei.com> <20210308210225.GF3479805@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210308210225.GF3479805@casper.infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 08-03-21 21:02:25, Matthew Wilcox wrote: > On Thu, Mar 04, 2021 at 07:40:53AM +0000, 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. > > There's another place we need to do this to ... > > +++ b/mm/page_alloc.c > @@ -5081,9 +5081,15 @@ void __free_pages(struct page *page, unsigned int order) > { > if (put_page_testzero(page)) > free_the_page(page, order); > - else if (!PageHead(page)) > - while (order-- > 0) > - free_the_page(page + (1 << order), order); > + else if (!PageHead(page)) { > + while (order-- > 0) { > + struct page *tail = page + (1 << order); > +#ifdef CONFIG_MEMCG > + tail->memcg_data = page->memcg_data; > +#endif > + free_the_page(tail, order); > + } > + } > } > EXPORT_SYMBOL(__free_pages); Hmm, I was not aware of this code. This is really a tricky code. > I wonder if we shouldn't initialise memcg_data on all subsequent pages > of non-compound allocations instead? Because I'm not sure this is the > only place that needs to be fixed. That would be safer for sure. Do you mean this as a replacement to the original patch? diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 913c2b9e5c72..d44dea2b8d22 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3135,8 +3135,21 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order) if (memcg && !mem_cgroup_is_root(memcg)) { ret = __memcg_kmem_charge(memcg, gfp, 1 << order); if (!ret) { + int nr_pages = 1 << order; page->memcg_data = (unsigned long)memcg | MEMCG_DATA_KMEM; + + /* + * Compound pages are normally split or freed + * via their head pages so memcg_data in in the + * head page should be sufficient but there + * are exceptions to the rule (see __free_pages). + * Non compound pages would need to copy memcg anyway. + */ + for (i = 1; i < nr_pages; i++) { + struct page * p = page + i; + p->memcg_data = page->memcg_data + } return 0; } css_put(&memcg->css); -- Michal Hocko SUSE Labs