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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