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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 23 Mar 2026, at 15:53, David Hildenbrand (Arm) wrote: > On 3/23/26 20:47, Zi Yan wrote: >> On 23 Mar 2026, at 15:41, David Hildenbrand (Arm) wrote: >> >>> On 3/23/26 20:06, Zi Yan wrote: >>>> READ_ONLY_THP_FOR_FS is no longer present, remove corresponding code= =2E >>>> >>>> Signed-off-by: Zi Yan >>>> --- >>>> mm/khugepaged.c | 159 +++++++++++----------------------------------= --- >>>> 1 file changed, 34 insertions(+), 125 deletions(-) >>>> >>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>>> index b2ac28ddd480..39f0b8959535 100644 >>>> --- a/mm/khugepaged.c >>>> +++ b/mm/khugepaged.c >>>> @@ -1899,7 +1899,7 @@ static enum scan_result collapse_file(struct m= m_struct *mm, unsigned long addr, >>>> int nr_none =3D 0; >>>> bool is_shmem =3D shmem_file(file); >>>> >>>> - VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); >>>> + VM_WARN_ON_ONCE(!is_shmem); >>> >>> Oh, but if that means that khugepaged cannot collapse large folios in= >>> FSes anymore, then this is the wrong approach I suppose? >>> >>> I would have assumed that we would now collapse for any files that >>> support large folios (in PMD size), not stopping to collapse entirely= =2E >> >> My understanding is that collapse_file() is only used for >> READ_ONLY_THP_FOR_FS. If FSes with large folio support also use it, >> I can replace IS_ENABLE with mapping_large_folio_support(). > > Otherwise we'd be losing support for THP collapse in files? We'd have t= o > cross fingers that readahead gives us some. > > So we have to be a bit careful here. We want khugepaged to collapse THP= s > in filesystems that support large folios even without READ_ONLY_THP_FOR= _FS. Based on[1], collapse_file() only works on read-only fd. So it is not as general as all files. If we do what you suggested, the function will be collapse read-only folios from FSes with large folio support. BTW, has anyone used/relied on collapse_file() on any FS with large folio= support? [1] https://elixir.bootlin.com/linux/v6.19.9/source/mm/khugepaged.c#L1956= Best Regards, Yan, Zi