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SubjectRe: [PATCH 1/6] mm: introduce kv[mz]alloc helpers
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On 01/19/2017 12:45 AM, Michal Hocko wrote:
> On Thu 19-01-17 00:37:08, John Hubbard wrote:
>>
>>
>> On 01/18/2017 12:21 AM, Michal Hocko wrote:
>>> On Tue 17-01-17 21:59:13, John Hubbard wrote:
> [...]
>>>> * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL should not be passed in.
>>>> * Passing in __GFP_REPEAT is supported, but note that it is ignored for small
>>>> * (<=64KB) allocations, during the kmalloc attempt.
>>>
>>>> __GFP_REPEAT is fully
>>>> * honored for all allocation sizes during the second part: the vmalloc attempt.
>>>
>>> this is not true to be really precise because vmalloc doesn't respect
>>> the given gfp mask all the way down (look at the pte initialization).
>>>
>>
>> I'm having some difficulty in locating that pte initialization part, am I on
>> the wrong code path? Here's what I checked, before making the claim about
>> __GFP_REPEAT being honored:
>>
>> kvmalloc_node
>> __vmalloc_node_flags
>> __vmalloc_node
>> __vmalloc_node_range
>> __vmalloc_area_node
> map_vm_area
> vmap_page_range
> vmap_page_range_noflush
> vmap_pud_range
> pud_alloc
> __pud_alloc
> pud_alloc_one
>
> pud will be allocated but the same pattern repeats on the pmd and pte
> levels. This is btw. one of the reasons why vmalloc with gfp flags is
> tricky!

Yes, I see that now, thank you for explaining, much appreciated. The flags are left
way behind in the code path.

So that leaves us with maybe this for documentation?

* Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL should not be passed in.
* Passing in __GFP_REPEAT is supported, and will cause the following behavior:
* for larger (>64KB) allocations, the first part (kmalloc) will do some
* retrying, before falling back to vmalloc.


>
> moreover
>> alloc_pages_node
>
> this is order-0 request so...
>
>> __alloc_pages_node
>> __alloc_pages
>> __alloc_pages_nodemask
>> __alloc_pages_slowpath
>>
>>
>> ...and __alloc_pages_slowpath does the __GFP_REPEAT handling:
>>
>> /*
>> * Do not retry costly high order allocations unless they are
>> * __GFP_REPEAT
>> */
>> if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_REPEAT))
>> goto nopage;
>
> ... this doesn't apply
>

yes, true.

thanks
john h

>

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