Messages in this thread | | | Date | Wed, 2 Dec 2015 16:07:30 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH 1/2] mm, oom: Give __GFP_NOFAIL allocations access to memory reserves |
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On Mon 30-11-15 14:17:03, David Rientjes wrote: > On Thu, 26 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? > > > > Are you suggesting to do? > > if (gfp_mask & __GFP_NOFAIL) { > > page = get_page_from_freelist(gfp_mask, order, > > ALLOC_NO_WATERMARKS|ALLOC_CPUSET, ac); > > /* > > * fallback to ignore cpuset if our nodes are > > * depleted > > */ > > if (!page) > > get_page_from_freelist(gfp_mask, order, > > ALLOC_NO_WATERMARKS, ac); > > } > > > > I am not really sure this worth complication. > > I'm objecting to the ability of a process that is doing a __GFP_NOFAIL > allocation, which has been disallowed access from allocating on certain > mems through cpusets, to cause an oom condition on those disallowed nodes, > yes.
That ability will be there even with the fallback mechanism. My primary objections was that the fallback is unnecessarily complex without any evidence that such a situation would happen in the real life often enought to bother about it. __GFP_NOFAIL allocations are and should be rare and any runaway triggerable from the userspace is a kernel bug.
Anyway, as you seem to feel really strongly about this I will post v2 with the above fallback. This is a superslow path anyway...
-- Michal Hocko SUSE Labs
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