From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751949AbdECLfF (ORCPT ); Wed, 3 May 2017 07:35:05 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:46768 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750981AbdECLe5 (ORCPT ); Wed, 3 May 2017 07:34:57 -0400 Subject: Re: [PATCH v2 1/2] mm: Uncharge poisoned pages To: Michal Hocko , Andi Kleen , Johannes Weiner 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> <3eb86373-dafc-6db9-82cd-84eb9e8b0d37@linux.vnet.ibm.com> <20170428134831.GB26705@dhcp22.suse.cz> <20170502185507.GB19165@dhcp22.suse.cz> Cc: Naoya Horiguchi , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, Vladimir Davydov From: Laurent Dufour Date: Wed, 3 May 2017 13:34:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170502185507.GB19165@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 17050311-0040-0000-0000-0000039C5051 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17050311-0041-0000-0000-00001FF59802 Message-Id: <20041995-0b68-7471-6439-ef327329c9f8@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-03_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1705030223 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/05/2017 20:55, Michal Hocko wrote: > On Tue 02-05-17 16:59:30, Laurent Dufour wrote: >> On 28/04/2017 15:48, Michal Hocko wrote: > [...] >>> This is getting quite hairy. What is the expected page count of the >>> hwpoison page? > > OK, so from the quick check of the hwpoison code it seems that the ref > count will be > 1 (from get_hwpoison_page). > >>> I guess we would need to update the VM_BUG_ON in the >>> memcg uncharge code to ignore the page count of hwpoison pages if it can >>> be arbitrary. >> >> Based on the experiment I did, page count == 2 when isolate_lru_page() >> succeeds, even in the case of a poisoned page. > > that would make some sense to me. The page should have been already > unmapped therefore but memory_failure increases the ref count and 1 is > for isolate_lru_page(). > >> In my case I think this >> is because the page is still used by the process which is calling madvise(). >> >> I'm wondering if I'm looking at the right place. May be the poisoned >> page should remain attach to the memory_cgroup until no one is using it. >> In that case this means that something should be done when the page is >> off-lined... I've to dig further here. > > No, AFAIU the page will not drop the reference count down to 0 in most > cases. Maybe there are some scenarios where this can happen but I would > expect that the poisoned page will be mapped and in use most of the time > and won't drop down 0. And then we should really uncharge it because it > will pin the memcg and make it unfreeable which doesn't seem to be what > we want. So does the following work reasonable? Andi, Johannes, what do > you think? I cannot say I would be really comfortable touching hwpoison > code as I really do not understand the workflow. Maybe we want to move > this uncharge down to memory_failure() right before we report success? > --- > From 8bf0791bcf35996a859b6d33fb5494e5b53de49d Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Tue, 2 May 2017 20:32:24 +0200 > Subject: [PATCH] hwpoison, memcg: forcibly uncharge LRU pages > > Laurent Dufour has noticed that hwpoinsoned pages are kept charged. In > his particular case he has hit a bad_page("page still charged to cgroup") > when onlining a hwpoison page. While this looks like something that shouldn't > happen in the first place because onlining hwpages and returning them to > the page allocator makes only little sense it shows a real problem. > > hwpoison pages do not get freed usually so we do not uncharge them (at > least not since 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API")). > Each charge pins memcg (since e8ea14cc6ead ("mm: memcontrol: take a css > reference for each charged page")) as well and so the mem_cgroup and the > associated state will never go away. Fix this leak by forcibly > uncharging a LRU hwpoisoned page in delete_from_lru_cache(). We also > have to tweak uncharge_list because it cannot rely on zero ref count > for these pages. > > Fixes: 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") > Reported-by: Laurent Dufour FWIW: Tested-by: Laurent Dufour > Signed-off-by: Michal Hocko > --- > mm/memcontrol.c | 2 +- > mm/memory-failure.c | 7 +++++++ > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 16c556ac103d..4cf26059adb1 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5527,7 +5527,7 @@ static void uncharge_list(struct list_head *page_list) > next = page->lru.next; > > VM_BUG_ON_PAGE(PageLRU(page), page); > - VM_BUG_ON_PAGE(page_count(page), page); > + VM_BUG_ON_PAGE(!PageHWPoison(page) && page_count(page), page); > > if (!page->mem_cgroup) > continue; > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index 8a6bd3a9eb1e..4497d9619bb4 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -541,6 +541,13 @@ static int delete_from_lru_cache(struct page *p) > */ > ClearPageActive(p); > ClearPageUnevictable(p); > + > + /* > + * Poisoned page might never drop its ref count to 0 so we have to > + * uncharge it manually from its memcg. > + */ > + mem_cgroup_uncharge(p); > + > /* > * drop the page count elevated by isolate_lru_page() > */ > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f198.google.com (mail-qk0-f198.google.com [209.85.220.198]) by kanga.kvack.org (Postfix) with ESMTP id 77BD66B02EE for ; Wed, 3 May 2017 07:34:58 -0400 (EDT) Received: by mail-qk0-f198.google.com with SMTP id r62so3565134qkh.19 for ; Wed, 03 May 2017 04:34:58 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id f35si19014352qtd.304.2017.05.03.04.34.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 03 May 2017 04:34:57 -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 v43BYLKn146499 for ; Wed, 3 May 2017 07:34:57 -0400 Received: from e06smtp11.uk.ibm.com (e06smtp11.uk.ibm.com [195.75.94.107]) by mx0a-001b2d01.pphosted.com with ESMTP id 2a7duq9hkq-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 03 May 2017 07:34:57 -0400 Received: from localhost by e06smtp11.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 3 May 2017 12:34:54 +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> <3eb86373-dafc-6db9-82cd-84eb9e8b0d37@linux.vnet.ibm.com> <20170428134831.GB26705@dhcp22.suse.cz> <20170502185507.GB19165@dhcp22.suse.cz> From: Laurent Dufour Date: Wed, 3 May 2017 13:34:48 +0200 MIME-Version: 1.0 In-Reply-To: <20170502185507.GB19165@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Message-Id: <20041995-0b68-7471-6439-ef327329c9f8@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Andi Kleen , Johannes Weiner Cc: Naoya Horiguchi , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, Vladimir Davydov On 02/05/2017 20:55, Michal Hocko wrote: > On Tue 02-05-17 16:59:30, Laurent Dufour wrote: >> On 28/04/2017 15:48, Michal Hocko wrote: > [...] >>> This is getting quite hairy. What is the expected page count of the >>> hwpoison page? > > OK, so from the quick check of the hwpoison code it seems that the ref > count will be > 1 (from get_hwpoison_page). > >>> I guess we would need to update the VM_BUG_ON in the >>> memcg uncharge code to ignore the page count of hwpoison pages if it can >>> be arbitrary. >> >> Based on the experiment I did, page count == 2 when isolate_lru_page() >> succeeds, even in the case of a poisoned page. > > that would make some sense to me. The page should have been already > unmapped therefore but memory_failure increases the ref count and 1 is > for isolate_lru_page(). > >> In my case I think this >> is because the page is still used by the process which is calling madvise(). >> >> I'm wondering if I'm looking at the right place. May be the poisoned >> page should remain attach to the memory_cgroup until no one is using it. >> In that case this means that something should be done when the page is >> off-lined... I've to dig further here. > > No, AFAIU the page will not drop the reference count down to 0 in most > cases. Maybe there are some scenarios where this can happen but I would > expect that the poisoned page will be mapped and in use most of the time > and won't drop down 0. And then we should really uncharge it because it > will pin the memcg and make it unfreeable which doesn't seem to be what > we want. So does the following work reasonable? Andi, Johannes, what do > you think? I cannot say I would be really comfortable touching hwpoison > code as I really do not understand the workflow. Maybe we want to move > this uncharge down to memory_failure() right before we report success? > --- > From 8bf0791bcf35996a859b6d33fb5494e5b53de49d Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Tue, 2 May 2017 20:32:24 +0200 > Subject: [PATCH] hwpoison, memcg: forcibly uncharge LRU pages > > Laurent Dufour has noticed that hwpoinsoned pages are kept charged. In > his particular case he has hit a bad_page("page still charged to cgroup") > when onlining a hwpoison page. While this looks like something that shouldn't > happen in the first place because onlining hwpages and returning them to > the page allocator makes only little sense it shows a real problem. > > hwpoison pages do not get freed usually so we do not uncharge them (at > least not since 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API")). > Each charge pins memcg (since e8ea14cc6ead ("mm: memcontrol: take a css > reference for each charged page")) as well and so the mem_cgroup and the > associated state will never go away. Fix this leak by forcibly > uncharging a LRU hwpoisoned page in delete_from_lru_cache(). We also > have to tweak uncharge_list because it cannot rely on zero ref count > for these pages. > > Fixes: 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") > Reported-by: Laurent Dufour FWIW: Tested-by: Laurent Dufour > Signed-off-by: Michal Hocko > --- > mm/memcontrol.c | 2 +- > mm/memory-failure.c | 7 +++++++ > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 16c556ac103d..4cf26059adb1 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5527,7 +5527,7 @@ static void uncharge_list(struct list_head *page_list) > next = page->lru.next; > > VM_BUG_ON_PAGE(PageLRU(page), page); > - VM_BUG_ON_PAGE(page_count(page), page); > + VM_BUG_ON_PAGE(!PageHWPoison(page) && page_count(page), page); > > if (!page->mem_cgroup) > continue; > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index 8a6bd3a9eb1e..4497d9619bb4 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -541,6 +541,13 @@ static int delete_from_lru_cache(struct page *p) > */ > ClearPageActive(p); > ClearPageUnevictable(p); > + > + /* > + * Poisoned page might never drop its ref count to 0 so we have to > + * uncharge it manually from its memcg. > + */ > + mem_cgroup_uncharge(p); > + > /* > * drop the page count elevated by isolate_lru_page() > */ > -- 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