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SubjectRe: [PATCH 1/2] mm, oom: Give __GFP_NOFAIL allocations access to memory reserves
On Wed, 25 Nov 2015, Michal Hocko wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8034909faad2..94b04c1e894a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2766,8 +2766,13 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
> goto out;
> }
> /* Exhausted what can be done so it's blamo time */
> - if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL))
> + if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) {
> *did_some_progress = 1;
> +
> + if (gfp_mask & __GFP_NOFAIL)
> + page = get_page_from_freelist(gfp_mask, order,
> + ALLOC_NO_WATERMARKS, ac);
> + }
> out:
> mutex_unlock(&oom_lock);
> return page;

Well, sure, that's one way to do it, but for cpuset users, wouldn't this
lead to a depletion of the first system zone since you've dropped
ALLOC_CPUSET and are doing ALLOC_NO_WATERMARKS in the same call?
get_page_from_freelist() shouldn't be doing any balancing over the set of
allowed zones. Can you justify depleting memory reserves on a zone
outside of the set of allowed cpuset mems rather than trying to drop
ALLOC_CPUSET first?


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