Re: [PATCH v1 03/10] mm: fs: remove filemap_nr_thps*() functions and their users

[David Hildenbrand (Arm)]

On 3/27/26 13:23, Lorenzo Stoakes (Oracle) wrote:
> On Thu, Mar 26, 2026 at 09:42:48PM -0400, Zi Yan wrote:
>> They are used by READ_ONLY_THP_FOR_FS to handle writes to FSes without
>> large folio support, so that read-only THPs created in these FSes are not
>> seen by the FSes when the underlying fd becomes writable. Now read-only PMD
>> THPs only appear in a FS with large folio support and the supported orders
>> include PMD_ORDRE.
> 
> Typo: PMD_ORDRE -> PMD_ORDER
> 
>>
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> 
> This looks obviously-correct since this stuff wouldn't have been invoked for
> large folio file systems before + they already had to handle it separately, and
> this function is only tied to CONFIG_READ_ONLY_THP_FOR_FS (+ a quick grep
> suggests you didn't miss anything), so:

There could now be a race between collapsing and the file getting opened
r/w.

Are we sure that all code can really deal with that?

IOW, "they already had to handle it separately" -- is that true?
khugepaged would have never collapse in writable files, so I wonder if
all code paths are prepared for that.

-- 
Cheers,

David