linux-kernel - Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure

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Message-ID: <2e5eda85-f1b3-4fc7-a378-346cfb3840e9@redhat.com>
Date: Thu, 12 Jun 2025 17:48:09 +0200
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, lorenzo.stoakes@...cle.com,
 Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com,
 dev.jain@....com, baohua@...nel.org, shuah@...nel.org, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure

On 12.06.25 17:46, Zi Yan wrote:
> On 11 Jun 2025, at 23:54, Baolin Wang wrote:
> 
>> When running the khugepaged selftest for shmem (./khugepaged all:shmem),
>> I encountered the following test failures:
>> "
>> Run test: collapse_full (khugepaged:shmem)
>> Collapse multiple fully populated PTE table.... Fail
>> ...
>> Run test: collapse_single_pte_entry (khugepaged:shmem)
>> Collapse PTE table with single PTE entry present.... Fail
>> ...
>> Run test: collapse_full_of_compound (khugepaged:shmem)
>> Allocate huge page... OK
>> Split huge page leaving single PTE page table full of compound pages... OK
>> Collapse PTE table full of compound pages.... Fail
>> "
>>
>> The reason for the failure is that, it will set MADV_NOHUGEPAGE to prevent
>> khugepaged from continuing to scan shmem VMA after khugepaged finishes
>> scanning in the wait_for_scan() function. Moreover, shmem requires a refault
>> to establish PMD mappings.
>>
>> However, after commit 2b0f922323cc, PMD mappings are prevented if the VMA is
> 
> Can you add the title of the commit? It is easier to understand the context.
> 
> 2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the hw/process/vma")
>

Probably checkpatch.pl would point out the same :)

-- 
Cheers,

David / dhildenb