Re: [PATCH V3] mm/thp: Allocate transparent hugepages on local node

[Vlastimil Babka]

On 01/20/2015 10:08 AM, Vlastimil Babka wrote:
> On 01/20/2015 06:52 AM, Aneesh Kumar K.V wrote:
>> Vlastimil Babka <vbabka@xxxxxxx> writes:
>> 
>> is that check correct ? ie, 
>> 
>> if ((gfp & GFP_TRANSHUGE) == GFP_TRANSHUGE)
>> 
>> may not always indicate transparent hugepage if defrag = 0 . With defrag
>> cleared, we remove __GFP_WAIT from GFP_TRANSHUGE.
> 
> Yep, that looks wrong. Sigh. I guess we can't spare an extra GFP flag to
> indicate TRANSHUGE?

I wanted to fix this in __alloc_pages_slowpath(), but actually there's no issue
(other than being quite subtle) - if defrag == 0 and thus we don't have
__GFP_WAIT, we reach "if (!wait) goto nopage;" and bail out before reaching the
checks for GFP_TRANSHUGE.

>> static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
>> {
>> 	return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
>> }
>> 
>> -aneesh
>> 
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