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Commit e0dd7d53 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
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mm, mempolicy: don't check cpuset seqlock where it doesn't matter 

Two wrappers of __alloc_pages_nodemask() are checking
task->mems_allowed_seq themselves to retry allocation that has raced
with a cpuset update.

This has been shown to be ineffective in preventing premature OOM's
which can happen in __alloc_pages_slowpath() long before it returns back
to the wrappers to detect the race at that level.

Previous patches have made __alloc_pages_slowpath() more robust, so we
can now simply remove the seqlock checking in the wrappers to prevent
further wrong impression that it can actually help.

Link: http://lkml.kernel.org/r/20170517081140.30654-7-vbabka@suse.cz


Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5f155f27

mm/mempolicy.c

+0 −16
Original line number Diff line number Diff line
@@ -1898,12 +1898,9 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma, 
	struct mempolicy *pol;

	struct page *page;

	int preferred_nid;

	unsigned int cpuset_mems_cookie;

	nodemask_t *nmask;



retry_cpuset:

	pol = get_vma_policy(vma, addr);

	cpuset_mems_cookie = read_mems_allowed_begin();



	if (pol->mode == MPOL_INTERLEAVE) {

		unsigned nid;
@@ -1945,8 +1942,6 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma, 
	page = __alloc_pages_nodemask(gfp, order, preferred_nid, nmask);

	mpol_cond_put(pol);

out:

	if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))

		goto retry_cpuset;

	return page;

}
@@ -1964,23 +1959,15 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma, 
 *	Allocate a page from the kernel page pool.  When not in

 *	interrupt context and apply the current process NUMA policy.

 *	Returns NULL when no page can be allocated.

 *

 *	Don't call cpuset_update_task_memory_state() unless

 *	1) it's ok to take cpuset_sem (can WAIT), and

 *	2) allocating for current task (not interrupt).

 */

struct page *alloc_pages_current(gfp_t gfp, unsigned order)

{

	struct mempolicy *pol = &default_policy;

	struct page *page;

	unsigned int cpuset_mems_cookie;



	if (!in_interrupt() && !(gfp & __GFP_THISNODE))

		pol = get_task_policy(current);



retry_cpuset:

	cpuset_mems_cookie = read_mems_allowed_begin();



	/*

	 * No reference counting needed for current->mempolicy

	 * nor system default_policy
@@ -1992,9 +1979,6 @@ struct page *alloc_pages_current(gfp_t gfp, unsigned order) 
				policy_node(gfp, pol, numa_node_id()),

				policy_nodemask(gfp, pol));



	if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))

		goto retry_cpuset;



	return page;

}

EXPORT_SYMBOL(alloc_pages_current);