linux-kernel - Re: [PATCH v11 0/6] Use pageblock_order for cma and alloc_contig

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Message-ID: <0C1D4567-F9EC-464E-8C5F-2971E9E956F3@nvidia.com>
Date:   Sun, 22 May 2022 15:33:30 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Eric Ren <renzhengeek@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Oscar Salvador <osalvador@...e.de>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v11 0/6] Use pageblock_order for cma and alloc_contig_range alignment.

On 22 May 2022, at 12:54, Zi Yan wrote:

> On 20 May 2022, at 19:41, Qian Cai wrote:
>
>> On Fri, May 20, 2022 at 05:56:52PM -0400, Zi Yan wrote:
>>> Do you have the page information like refcount, map count, mapping, index, and
>>> page flags? That would be more helpful. Thanks.
>>
>> page:fffffc200c7f8000 refcount:393 mapcount:1 mapping:0000000000000000 index:0xffffbb800 pfn:0x8039fe00
>> head:fffffc200c7f8000 order:9 compound_mapcount:0 compound_pincount:0
>> memcg:ffff40026005a000
>> anon flags: 0xbfffc000009001c(uptodate|dirty|lru|head|swapbacked|node=0|zone=2|lastcpupid=0xffff)
>> raw: 0bfffc000009001c fffffc2007b74048 fffffc2009c087c8 ffff08038dab9189
>> raw: 0000000ffffbb800 0000000000000000 0000018900000000 ffff40026005a000

OK. I replicated two scenarios, which can have the above page dump:
1. a PTE-mapped THP with 393 subpages mapped without any extra pin,
2. a PTE-mapped THP with 392 subpages mapped with an extra pin on the first subpage.

For scenario 1, there is no infinite looping on next-20220519 and next-20220520.

For scenario 2, an infinite loop happens on next-20220519, next-20220520, and next-20220520
with my fixup patch from another email, when the memory block, in which the page resides,
is being offlined. However, after reverting all my patches, the infinite loop remains.

So it looks to me that having an infinite loop during memory offline is not a regression
based on the experiments I have done. David Hildenbranch can correct me if I am wrong.
A better issue description, other than infinite loop during memory offlining, and a
better reproducer are needed for me to identify potential bugs in my code and fix them.

Of course, my fixup patch should be applied anyway.

Thanks for your testing.

--
Best Regards,
Yan, Zi

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