From: Zi Yan <ziy@nvidia.com>
To: Qian Cai <quic_qiancai@quicinc.com>
Cc: David Hildenbrand <david@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Vlastimil Babka <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
Eric Ren <renzhengeek@gmail.com>, Mike Rapoport <rppt@kernel.org>,
Oscar Salvador <osalvador@suse.de>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v11 0/6] Use pageblock_order for cma and alloc_contig_range alignment.
Date: Fri, 20 May 2022 10:13:51 -0400 [thread overview]
Message-ID: <A03D6267-5945-4A6A-9C55-5F3DDDB35CC2@nvidia.com> (raw)
In-Reply-To: <48D48FDC-B8DD-41C9-B56A-EBD7314883AB@nvidia.com>
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On 20 May 2022, at 9:43, Zi Yan wrote:
> On 20 May 2022, at 7:30, Qian Cai wrote:
>
>> On Thu, May 19, 2022 at 05:35:15PM -0400, Zi Yan wrote:
>>> Do you have a complete reproducer? From your printout, it is clear that a 512-page compound
>>> page caused the infinite loop, because the page was not migrated and the code kept
>>> retrying. But __alloc_contig_migrate_range() is supposed to return non-zero to tell the
>>> code the page cannot be migrated and the code will goto failed without retrying. It will be
>>> great you can share what exactly has run after boot, so that I can reproduce locally to
>>> identify what makes __alloc_contig_migrate_range() return 0 without migrating the page.
>>
>> The reproducer is just to run the same script I shared with you previously
>> multiple times instead. It is still quite reproducible here as it usually
>> happens within a hour.
>>
>> $ for i in `seq 1 100`; do ./flip_mem.py; done
Also, do you mind providing the page dump of the 512-page compound page? I would like
to know what page caused the issue.
Thanks.
>>
>>> Can you also try the patch below to see if it fixes the infinite loop?
>>>
>>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>>> index b3f074d1682e..abde1877bbcb 100644
>>> --- a/mm/page_isolation.c
>>> +++ b/mm/page_isolation.c
>>> @@ -417,10 +417,9 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
>>> order = 0;
>>> outer_pfn = pfn;
>>> while (!PageBuddy(pfn_to_page(outer_pfn))) {
>>> - if (++order >= MAX_ORDER) {
>>> - outer_pfn = pfn;
>>> - break;
>>> - }
>>> + /* abort if the free page cannot be found */
>>> + if (++order >= MAX_ORDER)
>>> + goto failed;
>>> outer_pfn &= ~0UL << order;
>>> }
>>> pfn = outer_pfn;
>>>
>>
>> Can you explain a bit how this patch is the right thing to do here? I am a
>> little bit worry about shooting into the dark. Otherwise, I'll be running
>> the off-by-one part over the weekend to see if that helps.
>
> The code kept retrying to migrate a 512-page compound page, so it seems to me
> that __alloc_contig_migrate_range() did not migrate the page but returned
> 0 every time, otherwise, if (ret) goto failed; would bail out of the loop
> already. The original code above assumed a free page can always be found after
> __alloc_contig_migrate_range(), so it will retry if no free page is found.
> But that assumption is not true from your infinite loop result, the new
> code quits retrying when no free page can be found.
>
> I will dig into it deeper to make sure it is the correct fix. I will
> update you when I am done.
>
> Thanks.
>
> --
> Best Regards,
> Yan, Zi
--
Best Regards,
Yan, Zi
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next prev parent reply other threads:[~2022-05-20 14:14 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-25 14:31 [PATCH v11 0/6] Use pageblock_order for cma and alloc_contig_range alignment Zi Yan
2022-04-25 14:31 ` [PATCH v11 1/6] mm: page_isolation: move has_unmovable_pages() to mm/page_isolation.c Zi Yan
2022-04-25 14:31 ` [PATCH v11 2/6] mm: page_isolation: check specified range for unmovable pages Zi Yan
2022-04-25 14:31 ` [PATCH v11 3/6] mm: make alloc_contig_range work at pageblock granularity Zi Yan
2022-04-29 13:54 ` Zi Yan
2022-05-24 19:00 ` Zi Yan
2022-05-25 17:41 ` Doug Berger
2022-05-25 17:53 ` Zi Yan
2022-05-25 21:03 ` Doug Berger
2022-05-25 21:11 ` Zi Yan
2022-05-26 17:34 ` Zi Yan
2022-05-26 19:46 ` Doug Berger
2022-04-25 14:31 ` [PATCH v11 4/6] mm: page_isolation: enable arbitrary range page isolation Zi Yan
2022-05-24 19:02 ` Zi Yan
2022-04-25 14:31 ` [PATCH v11 5/6] mm: cma: use pageblock_order as the single alignment Zi Yan
2022-04-25 14:31 ` [PATCH v11 6/6] drivers: virtio_mem: use pageblock size as the minimum virtio_mem size Zi Yan
2022-04-26 20:18 ` [PATCH v11 0/6] Use pageblock_order for cma and alloc_contig_range alignment Qian Cai
2022-04-26 20:26 ` Zi Yan
2022-04-26 21:08 ` Qian Cai
2022-04-26 21:38 ` Zi Yan
2022-04-27 12:41 ` Qian Cai
2022-04-27 13:10 ` Qian Cai
2022-04-27 13:27 ` Qian Cai
2022-04-27 13:30 ` Zi Yan
2022-04-27 21:04 ` Zi Yan
2022-04-28 12:33 ` Qian Cai
2022-04-28 12:39 ` Zi Yan
2022-04-28 16:19 ` Qian Cai
2022-04-29 13:38 ` Zi Yan
2022-05-19 20:57 ` Qian Cai
2022-05-19 21:35 ` Zi Yan
2022-05-19 23:24 ` Zi Yan
2022-05-20 11:30 ` Qian Cai
2022-05-20 13:43 ` Zi Yan
2022-05-20 14:13 ` Zi Yan [this message]
2022-05-20 19:41 ` Qian Cai
2022-05-20 21:56 ` Zi Yan
2022-05-20 23:41 ` Qian Cai
2022-05-22 16:54 ` Zi Yan
2022-05-22 19:33 ` Zi Yan
2022-05-24 16:59 ` Qian Cai
2022-05-10 1:03 ` Andrew Morton
2022-05-10 1:07 ` Zi Yan
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