From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f200.google.com (mail-wr0-f200.google.com [209.85.128.200]) by kanga.kvack.org (Postfix) with ESMTP id 9F0116B02E1 for ; Fri, 28 Apr 2017 05:32:40 -0400 (EDT) Received: by mail-wr0-f200.google.com with SMTP id 44so1819676wry.5 for ; Fri, 28 Apr 2017 02:32:40 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id i24si902211wrc.170.2017.04.28.02.32.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 28 Apr 2017 02:32:39 -0700 (PDT) Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v3S9T0LW096137 for ; Fri, 28 Apr 2017 05:32:38 -0400 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0a-001b2d01.pphosted.com with ESMTP id 2a3jv3j284-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 28 Apr 2017 05:32:37 -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 10:32:36 +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> <1493171698.4828.1.camel@gmail.com> <20170426023410.GA11619@hori1.linux.bs1.fc.nec.co.jp> <1493178300.4828.5.camel@gmail.com> <20170426044608.GA32451@hori1.linux.bs1.fc.nec.co.jp> <1493197141.16329.1.camel@gmail.com> From: Laurent Dufour Date: Fri, 28 Apr 2017 11:32:31 +0200 MIME-Version: 1.0 In-Reply-To: <1493197141.16329.1.camel@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Message-Id: Sender: owner-linux-mm@kvack.org List-ID: To: Balbir Singh , Naoya Horiguchi Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "akpm@linux-foundation.org" On 26/04/2017 10:59, Balbir Singh wrote: > On Wed, 2017-04-26 at 04:46 +0000, Naoya Horiguchi wrote: >> On Wed, Apr 26, 2017 at 01:45:00PM +1000, Balbir Singh wrote: >>>>>> static int delete_from_lru_cache(struct page *p) >>>>>> { >>>>>> + if (memcg_kmem_enabled()) >>>>>> + memcg_kmem_uncharge(p, 0); >>>>>> + >>>>> >>>>> The changelog is not quite clear, so we are uncharging a page using >>>>> memcg_kmem_uncharge for a page in swap cache/page cache? >>>> >>>> Hi Balbir, >>>> >>>> Yes, in the normal page lifecycle, uncharge is done in page free time. >>>> But in memory error handling case, in-use pages (i.e. swap cache and page >>>> cache) are removed from normal path and they don't pass page freeing code. >>>> So I think that this change is to keep the consistent charging for such a case. >>> >>> I agree we should uncharge, but looking at the API name, it seems to >>> be for kmem pages, why are we not using mem_cgroup_uncharge()? Am I missing >>> something? >> >> Thank you for pointing out. >> Actually I had the same question and this surely looks strange. >> But simply calling mem_cgroup_uncharge() here doesn't work because it >> assumes that page_refcount(p) == 0, which is not true in hwpoison context. >> We need some other clearer way or at least some justifying comment about >> why this is ok. >> > > We should call mem_cgroup_uncharge() after isolate_lru_page()/put_page(). Thanks for the review Naoya and Balbir, I changed the patch to call mem_cgroup_uncharge() once isolate_lru_page() succeeded, but before calling put_page(). It seems to work fine. > We could check if page_count() is 0 or force if required (!MF_RECOVERED && > !MF_DELAYED). We could even skip the VM_BUG_ON if the page is poisoned. This doesn't seem to be needed. Am I still missing something here ? 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