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Violators will be prosecuted for from ; Tue, 23 Jan 2018 18:15:39 -0000 From: Laurent Dufour Subject: Re: [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages References: <1493130472-22843-1-git-send-email-ldufour@linux.vnet.ibm.com> <1493130472-22843-3-git-send-email-ldufour@linux.vnet.ibm.com> <1493172615.4828.3.camel@gmail.com> <20170426031255.GB11619@hori1.linux.bs1.fc.nec.co.jp> <20170428063048.GA9399@dhcp22.suse.cz> <20180117150359.655bb93d8f1d663a2cd48c33@linux-foundation.org> Date: Tue, 23 Jan 2018 19:15:35 +0100 MIME-Version: 1.0 In-Reply-To: <20180117150359.655bb93d8f1d663a2cd48c33@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: <75179fb1-eb83-15b8-b7ba-d405745e1566@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Michal Hocko Cc: Naoya Horiguchi , Balbir Singh , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Wen Congyang Hi Andrew, On 18/01/2018 00:03, Andrew Morton wrote: > On Fri, 28 Apr 2017 08:30:48 +0200 Michal Hocko wrote: > >> On Wed 26-04-17 03:13:04, Naoya Horiguchi wrote: >>> On Wed, Apr 26, 2017 at 12:10:15PM +1000, Balbir Singh wrote: >>>> On Tue, 2017-04-25 at 16:27 +0200, Laurent Dufour wrote: >>>>> The commit b023f46813cd ("memory-hotplug: skip HWPoisoned page when >>>>> offlining pages") skip the HWPoisoned pages when offlining pages, but >>>>> this should be skipped when onlining the pages too. >>>>> >>>>> Signed-off-by: Laurent Dufour >>>>> --- >>>>> mm/memory_hotplug.c | 4 ++++ >>>>> 1 file changed, 4 insertions(+) >>>>> >>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>>>> index 6fa7208bcd56..741ddb50e7d2 100644 >>>>> --- a/mm/memory_hotplug.c >>>>> +++ b/mm/memory_hotplug.c >>>>> @@ -942,6 +942,10 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages, >>>>> if (PageReserved(pfn_to_page(start_pfn))) >>>>> for (i = 0; i < nr_pages; i++) { >>>>> page = pfn_to_page(start_pfn + i); >>>>> + if (PageHWPoison(page)) { >>>>> + ClearPageReserved(page); >>>> >>>> Why do we clear page reserved? Also if the page is marked PageHWPoison, it >>>> was never offlined to begin with? Or do you expect this to be set on newly >>>> hotplugged memory? Also don't we need to skip the entire pageblock? >>> >>> If I read correctly, to "skip HWPoiosned page" in commit b023f46813cd means >>> that we skip the page status check for hwpoisoned pages *not* to prevent >>> memory offlining for memblocks with hwpoisoned pages. That means that >>> hwpoisoned pages can be offlined. >> >> Is this patch actually correct? I am trying to wrap my head around it >> but it smells like it tries to avoid the problem rather than fix it >> properly. I might be wrong here of course but to me it sounds like >> poisoned page should simply be offlined and keep its poison state all >> the time. If the memory is hot-removed and added again we have lost the >> struct page along with the state which is the expected behavior. If it >> is still broken we will re-poison it. >> >> Anyway a patch to skip over poisoned pages during online makes perfect >> sense to me. The PageReserved fiddling around much less so. >> >> Or am I missing something. Let's CC Wen Congyang for the clarification >> here. > > Wen Congyang appears to have disappeared and this fix isn't yet > finalized. Can we all please revisit it and have a think about > Michal's questions? I tried to recreate the original issue, but there were a lot of changes done in this area since the last April. I was not able to offline a poisoned page because isolate_movable_page() is failing. I'll investigate that further... Cheers, Laurent. > Thanks. > > > From: Laurent Dufour > Subject: mm: skip HWPoisoned pages when onlining pages > > b023f46813cd ("memory-hotplug: skip HWPoisoned page when offlining pages") > skipped the HWPoisoned pages when offlining pages, but this should be > skipped when onlining the pages too. > > n-horiguchi@ah.jp.nec.com said: > > : If I read correctly, to "skip HWPoiosned page" in commit b023f46813cd > : means that we skip the page status check for hwpoisoned pages *not* to > : prevent memory offlining for memblocks with hwpoisoned pages. That > : means that hwpoisoned pages can be offlined. > : > : And another reason to clear PageReserved is that we could reuse the > : hwpoisoned page after onlining back with replacing the broken DIMM. In > : this usecase, we first do unpoisoning to clear PageHWPoison, but it > : doesn't work if PageReserved is set. My simple testing shows the BUG > : below in unpoisoning (without the ClearPageReserved): > : > : Unpoison: Software-unpoisoned page 0x18000 > : BUG: Bad page state in process page-types pfn:18000 > : page:ffffda5440600000 count:0 mapcount:0 mapping: (null) index:0x70006b599 > : flags: 0x1fffc00004081a(error|uptodate|dirty|reserved|swapbacked) > : raw: 001fffc00004081a 0000000000000000 000000070006b599 00000000ffffffff > : raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000 > : page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set > : bad because of flags: 0x800(reserved) > > Link: http://lkml.kernel.org/r/1493130472-22843-3-git-send-email-ldufour@linux.vnet.ibm.com > Signed-off-by: Laurent Dufour > Cc: Naoya Horiguchi > Cc: Andrey Vagin > Cc: Glauber Costa > Cc: Vladimir Davydov > Cc: Balbir Singh > Signed-off-by: Andrew Morton > --- > > mm/memory_hotplug.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff -puN mm/memory_hotplug.c~mm-skip-hwpoisoned-pages-when-onlining-pages mm/memory_hotplug.c > --- a/mm/memory_hotplug.c~mm-skip-hwpoisoned-pages-when-onlining-pages > +++ a/mm/memory_hotplug.c > @@ -696,6 +696,10 @@ static int online_pages_range(unsigned l > if (PageReserved(pfn_to_page(start_pfn))) > for (i = 0; i < nr_pages; i++) { > page = pfn_to_page(start_pfn + i); > + if (PageHWPoison(page)) { > + ClearPageReserved(page); > + continue; > + } > (*online_page_callback)(page); > onlined_pages++; > } > _ > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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