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Commit 6c18ba7a authored by Michal Hocko's avatar Michal Hocko Committed by Linus Torvalds
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mm: help __GFP_NOFAIL allocations which do not trigger OOM killer 

Now that __GFP_NOFAIL doesn't override decisions to skip the oom killer
we are left with requests which require to loop inside the allocator
without invoking the oom killer (e.g.  GFP_NOFS|__GFP_NOFAIL used by fs
code) and so they might, in very unlikely situations, loop for ever -
e.g.  other parallel request could starve them.

This patch tries to limit the likelihood of such a lockup by giving
these __GFP_NOFAIL requests a chance to move on by consuming a small
part of memory reserves.  We are using ALLOC_HARDER which should be
enough to prevent from the starvation by regular allocation requests,
yet it shouldn't consume enough from the reserves to disrupt high
priority requests (ALLOC_HIGH).

While we are at it, let's introduce a helper __alloc_pages_cpuset_fallback
which enforces the cpusets but allows to fallback to ignore them if the
first attempt fails.  __GFP_NOFAIL requests can be considered important
enough to allow cpuset runaway in order for the system to move on.  It
is highly unlikely that any of these will be GFP_USER anyway.

Link: http://lkml.kernel.org/r/20161220134904.21023-4-mhocko@kernel.org


Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 06ad276a

mm/page_alloc.c

+36 −10
Original line number Diff line number Diff line
@@ -3055,6 +3055,26 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...) 
	warn_alloc_show_mem(gfp_mask, nm);

}



static inline struct page *

__alloc_pages_cpuset_fallback(gfp_t gfp_mask, unsigned int order,

			      unsigned int alloc_flags,

			      const struct alloc_context *ac)

{

	struct page *page;



	page = get_page_from_freelist(gfp_mask, order,

			alloc_flags|ALLOC_CPUSET, ac);

	/*

	 * fallback to ignore cpuset restriction if our nodes

	 * are depleted

	 */

	if (!page)

		page = get_page_from_freelist(gfp_mask, order,

				alloc_flags, ac);



	return page;

}



static inline struct page *

__alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,

	const struct alloc_context *ac, unsigned long *did_some_progress)
@@ -3119,18 +3139,14 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, 
	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|ALLOC_CPUSET, ac);

		/*

			 * fallback to ignore cpuset restriction if our nodes

			 * are depleted

		 * Help non-failing allocations by giving them access to memory

		 * reserves

		 */

			if (!page)

				page = get_page_from_freelist(gfp_mask, order,

		if (gfp_mask & __GFP_NOFAIL)

			page = __alloc_pages_cpuset_fallback(gfp_mask, order,

					ALLOC_NO_WATERMARKS, ac);

	}

	}

out:

	mutex_unlock(&oom_lock);

	return page;
@@ -3785,6 +3801,16 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, 
		 */

		WARN_ON_ONCE(order > PAGE_ALLOC_COSTLY_ORDER);



		/*

		 * Help non-failing allocations by giving them access to memory

		 * reserves but do not use ALLOC_NO_WATERMARKS because this

		 * could deplete whole memory reserves which would just make

		 * the situation worse

		 */

		page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_HARDER, ac);

		if (page)

			goto got_pg;



		cond_resched();

		goto retry;

	}