From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Reza Arbab <arbab@linux.vnet.ibm.com>,
Yasuaki Ishimatsu <yasu.isimatu@gmail.com>,
qiuxishi@huawei.com, Igor Mammedov <imammedo@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early
Date: Wed, 13 Sep 2017 14:32:11 +0200 [thread overview]
Message-ID: <20170913123211.73ogviibe74wwxnl@dhcp22.suse.cz> (raw)
In-Reply-To: <25ffda93-0c0d-28b4-bd0b-7fc9df7d678a@suse.cz>
On Wed 13-09-17 14:19:19, Vlastimil Babka wrote:
> On 09/13/2017 02:14 PM, Michal Hocko wrote:
> >>>> Do you think that the changelog should be more clear about this?
> >>>
> >>> It certainly wouldn't hurt :)
> >>
> >> So what do you think about the following wording:
> >
> > Ups, wrong patch
> >
> >
> > From 8639496a834b4a7c24972ec23b17e50f0d6a304c Mon Sep 17 00:00:00 2001
> > From: Michal Hocko <mhocko@suse.com>
> > Date: Mon, 14 Aug 2017 10:46:12 +0200
> > Subject: [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early
> >
> > Memory offlining can fail just too eagerly under a heavy memory pressure.
> >
> > [ 5410.336792] page:ffffea22a646bd00 count:255 mapcount:252 mapping:ffff88ff926c9f38 index:0x3
> > [ 5410.336809] flags: 0x9855fe40010048(uptodate|active|mappedtodisk)
> > [ 5410.336811] page dumped because: isolation failed
> > [ 5410.336813] page->mem_cgroup:ffff8801cd662000
> > [ 5420.655030] memory offlining [mem 0x18b580000000-0x18b5ffffffff] failed
> >
> > Isolation has failed here because the page is not on LRU. Most probably
> > because it was on the pcp LRU cache or it has been removed from the LRU
> > already but it hasn't been freed yet. In both cases the page doesn't look
> > non-migrable so retrying more makes sense.
> >
> > __offline_pages seems rather cluttered when it comes to the retry
> > logic. We have 5 retries at maximum and a timeout. We could argue
> > whether the timeout makes sense but failing just because of a race when
> > somebody isoltes a page from LRU or puts it on a pcp LRU lists is just
> > wrong. It only takes it to race with a process which unmaps some pages
> > and remove them from the LRU list and we can fail the whole offline
> > because of something that is a temporary condition and actually not
> > harmful for the offline.
> >
> > Please note that unmovable pages should be already excluded during
> > start_isolate_page_range. We could argue that has_unmovable_pages is
> > racy and MIGRATE_MOVABLE check doesn't provide any hard guarantee either
> > but kernel zones (aka < ZONE_MOVABLE) will very likely detect unmovable
> > pages in most cases and movable zone shouldn't contain unmovable pages
> > at all. Some of those pages might be pinned but not for ever because
> > that would be a bug on its own. In any case the context is still
> > interruptible and so the userspace can easily bail out when the
> > operation takes too long. This is certainly better behavior than a
> > hardcoded retry loop which is racy.
> >
> > Fix this by removing the max retry count and only rely on the timeout
> > resp. interruption by a signal from the userspace. Also retry rather
> > than fail when check_pages_isolated sees some !free pages because those
> > could be a result of the race as well.
> >
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
>
> Yeah, that's better, thanks.
>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
Thanks. I will give it a day and repost the series. If somebody still
have some concerns please speak up.
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-09-13 12:32 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-04 8:21 [PATCH 0/2] mm, memory_hotplug: redefine memory offline retry logic Michal Hocko
2017-09-04 8:21 ` [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early Michal Hocko
2017-09-05 6:29 ` Anshuman Khandual
2017-09-05 7:13 ` Michal Hocko
2017-09-08 17:26 ` Vlastimil Babka
2017-09-11 8:17 ` Michal Hocko
2017-09-13 11:41 ` Vlastimil Babka
2017-09-13 12:10 ` Michal Hocko
2017-09-13 12:14 ` Michal Hocko
2017-09-13 12:19 ` Vlastimil Babka
2017-09-13 12:32 ` Michal Hocko [this message]
2017-09-04 8:21 ` [PATCH 2/2] mm, memory_hotplug: remove timeout from __offline_memory Michal Hocko
2017-09-04 8:58 ` Xishi Qiu
2017-09-04 9:01 ` Michal Hocko
2017-09-04 9:05 ` Xishi Qiu
2017-09-04 9:15 ` Michal Hocko
2017-09-05 5:46 ` Anshuman Khandual
2017-09-05 7:23 ` Michal Hocko
2017-09-05 8:54 ` Anshuman Khandual
2017-09-08 17:27 ` Vlastimil Babka
2017-09-18 7:08 [PATCH v2 0/2] mm, memory_hotplug: redefine memory offline retry logic Michal Hocko
2017-09-18 7:08 ` [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early Michal Hocko
2017-10-10 12:05 ` Michael Ellerman
2017-10-10 12:27 ` Michal Hocko
2017-10-11 2:37 ` Michael Ellerman
2017-10-11 5:19 ` Michael Ellerman
2017-10-11 14:05 ` Anshuman Khandual
2017-10-11 14:16 ` Michal Hocko
2017-10-11 6:51 ` Michal Hocko
2017-10-11 8:04 ` Vlastimil Babka
2017-10-11 8:13 ` Michal Hocko
2017-10-11 11:17 ` Vlastimil Babka
2017-10-11 11:24 ` Michal Hocko
2017-10-13 11:42 ` Michael Ellerman
2017-10-13 11:58 ` Michal Hocko
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