From: Zi Yan <ziy@nvidia.com>
To: "David Hildenbrand (Arm)" <david@kernel.org>
Cc: Vineet Agarwal <agarwal.vineet2006@gmail.com>,
akpm@linux-foundation.org, ljs@kernel.org, shuah@kernel.org,
linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] selftests/mm: khugepaged: initialize file contents via mmap
Date: Tue, 28 Apr 2026 16:22:45 -0400 [thread overview]
Message-ID: <83EFF919-7A84-4773-8C16-C51C15C3D987@nvidia.com> (raw)
In-Reply-To: <b4fad2c6-f2c1-484e-b6a1-97e763a39ba8@kernel.org>
On 28 Apr 2026, at 16:19, David Hildenbrand (Arm) wrote:
> On 4/28/26 22:17, Zi Yan wrote:
>> On 28 Apr 2026, at 16:07, David Hildenbrand (Arm) wrote:
>>
>>> On 4/28/26 21:56, Zi Yan wrote:
>>>>
>>>>
>>>> This patch breaks the khugepaged test for READ_ONLY_THP_FOR_FS.
>>>>
>>>> When I ran sudo ./khugepaged all:file ~/ on ext4,
>>>>
>>>> collapse_max_ptes_none (khugepaged:file) fails.
>>>
>>> madvise() still works? Is it maybe because of dirty folios? (but that should
>>> also be the case on write ...)
>>
>> I asked codex instead.
>>
>> Basically, mmap(MMAP_SHARED) makes the written folio dirty and the folio
>> survives the later drop_caches. Adding msync() fixes the issue.
>
> But why doesn't the write() make the folios dirty? Or are we running into some
> race condition where the old code just worked by chance?
>
The fd is opened with O_DSYNC, so the data from write() is transferred to
disk when write() returns.
Best Regards,
Yan, Zi
next prev parent reply other threads:[~2026-04-28 20:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-28 13:31 [PATCH v4] selftests/mm: khugepaged: initialize file contents via mmap Vineet Agarwal
2026-04-28 13:49 ` David Hildenbrand (Arm)
2026-04-28 19:56 ` Zi Yan
2026-04-28 20:07 ` David Hildenbrand (Arm)
2026-04-28 20:17 ` Zi Yan
2026-04-28 20:19 ` David Hildenbrand (Arm)
2026-04-28 20:22 ` Zi Yan [this message]
2026-04-28 20:23 ` Zi Yan
2026-04-29 6:24 ` David Hildenbrand (Arm)
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