From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id ED3506B02EE for ; Fri, 28 Apr 2017 05:17:44 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id 44so1787903wry.5 for ; Fri, 28 Apr 2017 02:17:44 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id n188si5874663wmg.3.2017.04.28.02.17.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 28 Apr 2017 02:17:43 -0700 (PDT) Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v3S9Dppx131450 for ; Fri, 28 Apr 2017 05:17:42 -0400 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0b-001b2d01.pphosted.com with ESMTP id 2a3hj06ch0-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 28 Apr 2017 05:17:42 -0400 Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 28 Apr 2017 10:17:40 +0100 Subject: Re: [PATCH v2 1/2] mm: Uncharge poisoned pages References: <1493130472-22843-1-git-send-email-ldufour@linux.vnet.ibm.com> <1493130472-22843-2-git-send-email-ldufour@linux.vnet.ibm.com> <20170427143721.GK4706@dhcp22.suse.cz> <87pofxk20k.fsf@firstfloor.org> <20170428060755.GA8143@dhcp22.suse.cz> <20170428073136.GE8143@dhcp22.suse.cz> From: Laurent Dufour Date: Fri, 28 Apr 2017 11:17:34 +0200 MIME-Version: 1.0 In-Reply-To: <20170428073136.GE8143@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Message-Id: <3eb86373-dafc-6db9-82cd-84eb9e8b0d37@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Andi Kleen Cc: Naoya Horiguchi , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, Johannes Weiner , Vladimir Davydov On 28/04/2017 09:31, Michal Hocko wrote: > [CC Johannes and Vladimir - the patch is > http://lkml.kernel.org/r/1493130472-22843-2-git-send-email-ldufour@linux.vnet.ibm.com] > > On Fri 28-04-17 08:07:55, Michal Hocko wrote: >> On Thu 27-04-17 13:51:23, Andi Kleen wrote: >>> Michal Hocko writes: >>> >>>> On Tue 25-04-17 16:27:51, Laurent Dufour wrote: >>>>> When page are poisoned, they should be uncharged from the root memory >>>>> cgroup. >>>>> >>>>> This is required to avoid a BUG raised when the page is onlined back: >>>>> BUG: Bad page state in process mem-on-off-test pfn:7ae3b >>>>> page:f000000001eb8ec0 count:0 mapcount:0 mapping: (null) >>>>> index:0x1 >>>>> flags: 0x3ffff800200000(hwpoison) >>>> >>>> My knowledge of memory poisoning is very rudimentary but aren't those >>>> pages supposed to leak and never come back? In other words isn't the >>>> hoplug code broken because it should leave them alone? >>> >>> Yes that would be the right interpretation. If it was really offlined >>> due to a hardware error the memory will be poisoned and any access >>> could cause a machine check. >> >> OK, thanks for the clarification. Then I am not sure the patch is >> correct. Why do we need to uncharge that page at all? > > Now, I have realized that we actually want to uncharge that page because > it will pin the memcg and we do not want to have that memcg and its > whole hierarchy pinned as well. This used to work before the charge > rework 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") I guess > because we used to uncharge on page cache removal. > > I do not think the patch is correct, though. memcg_kmem_enabled() will > check whether kmem accounting is enabled and we are talking about page > cache pages here. You should be using mem_cgroup_uncharge instead. Thanks for the review Michal. I was not comfortable either with this patch. I did some tests calling mem_cgroup_uncharge() when isolate_lru_page() succeeds only, so not calling it if isolate_lru_page() failed. This seems to work as well, so if everyone agree on that, I'll send a new version soon. Cheers, Laurent. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org