From: Michal Hocko <mhocko@kernel.org>
To: Baoquan He <bhe@redhat.com>
Cc: David Hildenbrand <david@redhat.com>,
linux-mm@kvack.org, pifang@redhat.com,
linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
aarcange@redhat.com, Mel Gorman <mgorman@suse.de>,
Vlastimil Babka <vbabka@suse.cz>, Hugh Dickins <hughd@google.com>
Subject: Re: Memory hotplug softlock issue
Date: Mon, 19 Nov 2018 13:51:21 +0100 [thread overview]
Message-ID: <20181119125121.GK22247@dhcp22.suse.cz> (raw)
In-Reply-To: <20181119124033.GJ22247@dhcp22.suse.cz>
On Mon 19-11-18 13:40:33, Michal Hocko wrote:
> On Mon 19-11-18 18:52:02, Baoquan He wrote:
> [...]
>
> There are few stacks directly in the offline path but those should be
> OK.
> The real culprit seems to be the swap in code
>
> > [ +1.734416] CPU: 255 PID: 5558 Comm: stress Tainted: G L 4.20.0-rc2+ #7
> > [ +0.007927] Hardware name: 9008/IT91SMUB, BIOS BLXSV512 03/22/2018
> > [ +0.006297] Call Trace:
> > [ +0.002537] dump_stack+0x46/0x60
> > [ +0.003386] __migration_entry_wait.cold.65+0x5/0x14
> > [ +0.005043] do_swap_page+0x84e/0x960
> > [ +0.003727] ? arch_tlb_finish_mmu+0x29/0xc0
> > [ +0.006412] __handle_mm_fault+0x933/0x1330
> > [ +0.004265] handle_mm_fault+0xc4/0x250
> > [ +0.003915] __do_page_fault+0x2b7/0x510
> > [ +0.003990] do_page_fault+0x2c/0x110
> > [ +0.003729] ? page_fault+0x8/0x30
> > [ +0.003462] page_fault+0x1e/0x30
>
> There are many traces to this path. We are
> /*
> * Once page cache replacement of page migration started, page_count
> * *must* be zero. And, we don't want to call wait_on_page_locked()
> * against a page without get_page().
> * So, we use get_page_unless_zero(), here. Even failed, page fault
> * will occur again.
> */
> if (!get_page_unless_zero(page))
> goto out;
> pte_unmap_unlock(ptep, ptl);
> wait_on_page_locked(page);
>
> taking a reference to the page under the migration. I have to think
> about this much more but I suspec this is just calling for a problem.
>
> Cc migration experts. For you background information. We are seeing
> memory offline not being able to converge because few heavily used pages
> fail to migrate away - e.g. http://lkml.kernel.org/r/20181116012433.GU2653@MiWiFi-R3L-srv
> A debugging page to dump stack for these pages http://lkml.kernel.org/r/20181116091409.GD14706@dhcp22.suse.cz
> shows that references are taken from the swap in code (above). How are
> we supposed to converge when the swapin code waits for the migration to
> finish with the reference count elevated?
Just to clarify. This is not only about swapin obviously. Any caller of
__migration_entry_wait is affected the same way AFAICS.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-11-19 12:51 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-14 7:09 Memory hotplug softlock issue Baoquan He
2018-11-14 7:16 ` Baoquan He
2018-11-14 8:18 ` David Hildenbrand
2018-11-14 9:00 ` Baoquan He
2018-11-14 9:25 ` David Hildenbrand
2018-11-14 9:41 ` Michal Hocko
2018-11-14 9:48 ` David Hildenbrand
2018-11-14 10:04 ` Michal Hocko
2018-11-14 9:01 ` Michal Hocko
2018-11-14 9:22 ` David Hildenbrand
2018-11-14 9:37 ` Michal Hocko
2018-11-14 9:39 ` David Hildenbrand
2018-11-14 14:52 ` Baoquan He
2018-11-14 15:00 ` Michal Hocko
2018-11-15 5:10 ` Baoquan He
2018-11-15 7:30 ` Michal Hocko
2018-11-15 7:53 ` Baoquan He
2018-11-15 8:30 ` Michal Hocko
2018-11-15 9:42 ` David Hildenbrand
2018-11-15 9:52 ` Baoquan He
2018-11-15 9:53 ` David Hildenbrand
2018-11-15 13:12 ` Baoquan He
2018-11-15 13:19 ` Michal Hocko
2018-11-15 13:23 ` Baoquan He
2018-11-15 14:25 ` Michal Hocko
2018-11-15 13:38 ` Baoquan He
2018-11-15 14:32 ` Michal Hocko
2018-11-15 14:34 ` Baoquan He
2018-11-16 1:24 ` Baoquan He
2018-11-16 9:14 ` Michal Hocko
2018-11-17 4:22 ` Baoquan He
2018-11-19 10:52 ` Baoquan He
2018-11-19 12:40 ` Michal Hocko
2018-11-19 12:51 ` Michal Hocko [this message]
2018-11-19 14:10 ` Michal Hocko
2018-11-19 16:36 ` Vlastimil Babka
2018-11-19 16:46 ` Michal Hocko
2018-11-19 16:46 ` Vlastimil Babka
2018-11-19 16:48 ` Vlastimil Babka
2018-11-19 17:01 ` Michal Hocko
2018-11-19 17:33 ` Michal Hocko
2018-11-19 20:34 ` Hugh Dickins
2018-11-19 20:59 ` Michal Hocko
2018-11-20 1:56 ` Baoquan He
2018-11-20 5:44 ` Hugh Dickins
2018-11-20 13:38 ` Vlastimil Babka
2018-11-20 13:58 ` Baoquan He
2018-11-20 14:05 ` Michal Hocko
2018-11-20 14:12 ` Baoquan He
2018-11-21 1:21 ` Hugh Dickins
2018-11-21 1:08 ` Hugh Dickins
2018-11-21 3:20 ` Hugh Dickins
2018-11-21 17:31 ` Michal Hocko
2018-11-22 1:53 ` Hugh Dickins
2018-11-14 10:00 ` Michal Hocko
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