Re: [PATCH v1 02/10] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check

Lance Yang
2026-03-27T07:35:46Z

On 2026/3/27 15:29, Lance Yang wrote:
>
> On Thu, Mar 26, 2026 at 09:42:47PM -0400, Zi Yan wrote:
>> collapse_file() requires FSes supporting large folio with at least
>> PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. shmem with
>> huge option turned on also sets large folio order on mapping, so the check
>> also applies to shmem.
>>
>> While at it, replace VM_BUG_ON with returning failure values.
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
>> mm/khugepaged.c | 7 +++++--
>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index d06d84219e1b..45b12ffb1550 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -1899,8 +1899,11 @@ 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_BUG_ON(start & (HPAGE_PMD_NR - 1));
>> + /* "huge" shmem sets mapping folio order and passes the check below */
>> + if (mapping_max_folio_order(mapping) < PMD_ORDER)
>> + return SCAN_FAIL;
>
> Yep, for shmem inodes, if the mount has huge= enabled, inode creation
> marks the mapping are large-folio capable:

Oops, s/are/as/

>
> /* Don't consider 'deny' for emergencies and 'force' for testing */
> if (sbinfo->huge)
> mapping_set_large_folios(inode->i_mapping);
>
> LGTM!
>
> Reviewed-by: Lance Yang <lance.yang@linux.dev>