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. >>>> >>>> Signed-off-by: Zi Yan <[email protected]> >>>> --- >>>> 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 >>>> mm_struct *mm, unsigned long addr, >>>> int nr_none = 0; >>>> bool is_shmem = 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. >> >> 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 to > cross fingers that readahead gives us some. > > So we have to be a bit careful here. We want khugepaged to collapse THPs > 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
