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From:   Zi Yan <ziy@nvidia.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>
Subject: Re: v5.18-rc1: migratepages triggers VM_BUG_ON_FOLIO(folio_nr_pages(old) != nr_pages)
Date:   Mon, 04 Apr 2022 10:47:20 -0400
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On 4 Apr 2022, at 10:29, Matthew Wilcox wrote:

> On Mon, Apr 04, 2022 at 10:05:00AM -0400, Zi Yan wrote:
>> On 4 Apr 2022, at 9:29, Naoya Horiguchi wrote:
>>> I found that the below VM_BUG_ON_FOLIO is triggered on v5.18-rc1
>>> (and also reproducible with mmotm on 3/31).
>>> I have no idea about the bug's mechanism, but it seems not to be
>>> shared in LKML yet, so let me just share. config.gz is attached.
>>>
>>> [   48.206424] page:0000000021452e3a refcount:6 mapcount:0 mapping:00=
0000003aaf5253 index:0x0 pfn:0x14e600
>>> [   48.213316] head:0000000021452e3a order:9 compound_mapcount:0 comp=
ound_pincount:0
>>> [   48.218830] aops:xfs_address_space_operations [xfs] ino:dee dentry=
 name:"libc.so.6"
>>> [   48.225098] flags: 0x57ffffc0012027(locked|referenced|uptodate|act=
ive|private|head|node=3D1|zone=3D2|lastcpupid=3D0x1fffff)
>>> [   48.232792] raw: 0057ffffc0012027 0000000000000000 dead00000000012=
2 ffff8a0dc9a376b8
>>> [   48.238464] raw: 0000000000000000 ffff8a0dc6b23d20 00000006fffffff=
f 0000000000000000
>>> [   48.244109] page dumped because: VM_BUG_ON_FOLIO(folio_nr_pages(ol=
d) !=3D nr_pages)
>>> [   48.249196] ------------[ cut here ]------------
>>> [   48.251240] kernel BUG at mm/memcontrol.c:6857!
>>> [   48.260535] RIP: 0010:mem_cgroup_migrate+0x217/0x320
>>> [   48.286942] Call Trace:
>>> [   48.287665]  <TASK>
>>> [   48.288255]  iomap_migrate_page+0x64/0x190
>>> [   48.289366]  move_to_new_page+0xa3/0x470
>>
>> Is it because migration code assumes all THPs have order=3DHPAGE_PMD_O=
RDER?
>> Would the patch below fix the issue?
>
> This looks entirely plausible to me!  I do have changes in this area,
> but clearly I should have submitted them earlier.  Let's get these fixe=
s
> in as they are.
>
> Is there a test suite that tests page migration?  I usually use xfstest=
s
> and it does no page migration at all (at least 'git grep migrate'
> finds nothing useful).

https://github.com/linux-test-project/ltp has some migrate_pages and move=
_pages
tests. You can run them after install ltp:
sudo ./runltp -f syscalls -s migrate_pages and
sudo ./runltp -f sys calls -s move_pages


--
Best Regards,
Yan, Zi

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