On 01/20/2015 06:52 AM, Aneesh Kumar K.V wrote:
> Vlastimil Babka <vbabka@xxxxxxx> writes:
>
>> On 01/17/2015 01:02 AM, Andrew Morton wrote:
>>> On Fri, 16 Jan 2015 12:56:36 +0530 "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
>>>
>>>> This make sure that we try to allocate hugepages from local node if
>>>> allowed by mempolicy. If we can't, we fallback to small page allocation
>>>> based on mempolicy. This is based on the observation that allocating pages
>>>> on local node is more beneficial than allocating hugepages on remote node.
>>>
>>> The changelog is a bit incomplete. It doesn't describe the current
>>> behaviour, nor what is wrong with it. What are the before-and-after
>>> effects of this change?
>>>
>>> And what might be the user-visible effects?
>>>
>>>> --- a/mm/mempolicy.c
>>>> +++ b/mm/mempolicy.c
>>>> @@ -2030,6 +2030,46 @@ retry_cpuset:
>>>> return page;
>>>> }
>>>>
>>>> +struct page *alloc_hugepage_vma(gfp_t gfp, struct vm_area_struct *vma,
>>>> + unsigned long addr, int order)
>>>
>>> alloc_pages_vma() is nicely documented. alloc_hugepage_vma() is not
>>> documented at all. This makes it a bit had for readers to work out the
>>> difference!
>>>
>>> Is it possible to scrunch them both into the same function? Probably
>>> too messy?
>>
>> Hm that could work, alloc_pages_vma already has an if (MPOL_INTERLEAVE) part, so
>> just put the THP specialities into an "else if (huge_page)" part there?
>>
>> You could probably test for GFP_TRANSHUGE the same way as __alloc_pages_slowpath
>> does. There might be false positives theoretically, but is there anything else
>> that would use these flags and not be a THP?
>>
>
> 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?
> 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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