mm, mempolicy: don't check cpuset seqlock where it doesn't matter (e0dd7d53) · Commits · 戴 / test

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:

Vlastimil Babka <vbabka@suse.cz> Acked-by:

Michal 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:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

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 @@ retry_cpuset:
		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 @@ out:
		* 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 @@ retry_cpuset:
		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);

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