Re: [RFC PATCH 02/11] mm/khugepaged: remove READ_ONLY_THP_FOR_FS code in collapse_file()

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 3/24/26 8:12 AM, Zi Yan wrote:
> On 23 Mar 2026, at 17:21, David Hildenbrand (Arm) wrote:
> 
>> On 3/23/26 22:11, Zi Yan wrote:
>>> On 23 Mar 2026, at 17:05, David Hildenbrand (Arm) wrote:
>>>
>>>> On 3/23/26 22:02, Matthew Wilcox wrote:
>>>>>
>>>>> Not necessarily that lucky; if you set VM_HUGEPAGE,
>>>>> do_sync_mmap_readahead() will allocate PMD-sized folios automatically.
>>>>> On busy database servers (and is there any other kind?), khugepaged
>>>>> takes too long to run and find opportunities to collapse text pages.
>>>>> Like, days.
>>>>
>>>> Yes, in particular given that the default khugepaged settings are awful.
>>>>
>>>>>
>>>>>
>>>>> I think the test needs to be:
>>>>>
>>>>> 	if (mapping_max_folio_order(mapping) >= PMD_ORDER)
>>>
>>> This is very helpful, since I was thinking about using
>>> mapping_large_folio_support().
>>>
>>>>>
>>>>> as there can be cases of filesystems which support up to, say, 64KiB,
>>>>> but not all the way up to 2MiB.  I disapprove of this situation, but
>>>>> this is where we are right now.
>>>>
>>>> Right, that's what I had in mind.
>>>
>>> Does Nico’s mTHP support for khugepaged include changes to collapse_file()?
>>> That might change the above test.
>>
>> At least not regarding adding support for other folio sizes. Baolin
>> (IIRC) had a version for shmem support, but that will come after Nico's
>> series was merged.

Right. Here is the link to the RFC version:

https://lore.kernel.org/all/cover.1755677674.git.baolin.wang@linux.alibaba.com/

Moreover, I have further updated my local tree based on Nico's series. I 
will send out the new version once his series is merged.