Re: [PATCH] mm: remove out-dated document of __GFP_NOFAIL

[Wei Yang]

On Thu, Aug 27, 2026 at 10:03:41AM +0200, Vlastimil Babka (SUSE) wrote:
>On 8/27/26 9:49 AM, Wei Yang wrote:
>> On Thu, Aug 27, 2026 at 09:35:26AM +0200, Vlastimil Babka (SUSE) wrote:
>>> On 8/27/26 5:05 AM, Wei Yang wrote:
>>>> Commit ee040cbd6e48 ("mm/page_alloc: don't warn about large allocations
>>>> with __GFP_NOFAIL") remove a warning on allocating large folio with
>>>> __GFP_NOFAIL, which is adjusted by commit 903edea6c53f ("mm: warn about
>>>> illegal __GFP_NOFAIL usage in a more appropriate location and manner").
>>>
>>> "which is adjusted by commit" sounds as 903edea6c53f came later than
>>> ee040cbd6e48, but it's the opposite. Maybe say "which was placed there"?
>>>
>> 
>> Got it.
>> 
>>>> While in that commit, it also documented this behavior which is
>>>> out-dated now.
>>>>
>>>> Adjust the document to align to current code, and adjust the comment
>>>> while at it.
>>>>
>>>> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
>>>> Cc: Baokun Li <libaokun1@xxxxxxxxxx>
>>>> ---
>>>>  include/linux/gfp_types.h | 2 --
>>>>  mm/page_alloc.c           | 2 +-
>>>>  2 files changed, 1 insertion(+), 3 deletions(-)
>>>>
>>>> diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
>>>> index 190191411009..24fde8eb73df 100644
>>>> --- a/include/linux/gfp_types.h
>>>> +++ b/include/linux/gfp_types.h
>>>> @@ -243,8 +243,6 @@ enum {
>>>>   * used only when there is no reasonable failure policy) but it is
>>>>   * definitely preferable to use the flag rather than opencode endless
>>>>   * loop around allocator.
>>>> - * Allocating pages from the buddy with __GFP_NOFAIL and order > 1 is
>>>> - * not supported. Please consider using kvmalloc() instead.
>>>
>>> I'm not sure if we want to simply remove the lines, or rather say it's
>>> discouraged (instead of not supported) and still suggest kvmalloc() if
>>> possible.
>>>
>> 
>> Reasonable.
>> 
>> As mentioned in [1], kvmalloc() maybe not suitable for some cases, I would
>> suggest below change.
>> 
>>  * Allocating pages from the buddy with __GFP_NOFAIL and order > 1 is
>>  * discouraged. Please consider using kvmalloc() instead if possible.
>
>Yeah that's great! Thanks.
>

Thanks, I will wait a while for other comment before sending v2.

>> Or, you prefer only s/supported/discouraged/ ?
>> 
>> [1]: https://lore.kernel.org/all/aQTHMI3t5mNXp0M1@xxxxxxxxxxxxxxxxxxxx
>> 
>>>>   */
>>>>  #define __GFP_IO	((__force gfp_t)___GFP_IO)
>>>>  #define __GFP_FS	((__force gfp_t)___GFP_FS)
>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>> index ab385bc252cc..146f7e0a9462 100644
>>>> --- a/mm/page_alloc.c
>>>> +++ b/mm/page_alloc.c
>>>> @@ -4804,7 +4804,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>>>  
>>>>  	if (unlikely(nofail)) {
>>>>  		/*
>>>> -		 * Also we don't support __GFP_NOFAIL without __GFP_DIRECT_RECLAIM,
>>>> +		 * We don't support __GFP_NOFAIL without __GFP_DIRECT_RECLAIM,
>>>>  		 * otherwise, we may result in lockup.
>>>>  		 */
>>>>  		WARN_ON_ONCE(!can_direct_reclaim);
>> 

-- 
Wei Yang
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