linux-kernel - Re: Memory hotplug softlock issue

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Date:   Wed, 14 Nov 2018 16:00:29 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        aarcange@...hat.com
Subject: Re: Memory hotplug softlock issue

On Wed 14-11-18 22:52:50, Baoquan He wrote:
> On 11/14/18 at 10:01am, Michal Hocko wrote:
> > I have seen an issue when the migration cannot make a forward progress
> > because of a glibc page with a reference count bumping up and down. Most
> > probable explanation is the faultaround code. I am working on this and
> > will post a patch soon. In any case the migration should converge and if
> > it doesn't do then there is a bug lurking somewhere.
> > 
> > Failing on ENOMEM is a questionable thing. I haven't seen that happening
> > wildly but if it is a case then I wouldn't be opposed.
> 
> Applied your debugging patches, it helps a lot to printing message.
> 
> Below is the dmesg log about the migrating failure. It can't pass
> migrate_pages() and loop forever.
> 
> [  +0.083841] migrating pfn 10fff7d0 failed 
> [  +0.000005] page:ffffea043ffdf400 count:208 mapcount:201 mapping:ffff888dff4bdda8 index:0x2
> [  +0.012689] xfs_address_space_operations [xfs] 
> [  +0.000030] name:"stress" 
> [  +0.004556] flags: 0x5fffffc0000004(uptodate)
> [  +0.007339] raw: 005fffffc0000004 ffffc900000e3d80 ffffc900000e3d80 ffff888dff4bdda8
> [  +0.009488] raw: 0000000000000002 0000000000000000 000000cb000000c8 ffff888e7353d000
> [  +0.007726] page->mem_cgroup:ffff888e7353d000
> [  +0.084538] migrating pfn 10fff7d0 failed 
> [  +0.000006] page:ffffea043ffdf400 count:210 mapcount:201 mapping:ffff888dff4bdda8 index:0x2
> [  +0.012798] xfs_address_space_operations [xfs] 
> [  +0.000034] name:"stress" 
> [  +0.004524] flags: 0x5fffffc0000004(uptodate)
> [  +0.007068] raw: 005fffffc0000004 ffffc900000e3d80 ffffc900000e3d80 ffff888dff4bdda8
> [  +0.009359] raw: 0000000000000002 0000000000000000 000000cb000000c8 ffff888e7353d000
> [  +0.007728] page->mem_cgroup:ffff888e7353d000

I wouldn't be surprised if this was a similar/same issue I've been
chasing recently. Could you try to disable faultaround to see if that
helps. It seems that it helped in my particular case but I am still
waiting for the final good-to-go to post the patch as I do not own the
workload which triggered that issue.
-- 
Michal Hocko
SUSE Labs