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Commit a1a46184 authored by Mel Gorman's avatar Mel Gorman Committed by Ingo Molnar
Browse files

mm: numa: Do not migrate or account for hinting faults on the zero page 



The zero page is not replicated between nodes and is often shared between
processes. The data is read-only and likely to be cached in local CPUs
if heavily accessed meaning that the remote memory access cost is less
of a concern. This patch prevents trapping faults on the zero pages. For
tasks using the zero page this will reduce the number of PTE updates,
TLB flushes and hinting faults.

Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
[ Correct use of is_huge_zero_page]
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-13-git-send-email-mgorman@suse.de


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent f123d74a

mm/huge_memory.c

+9 −1
Original line number Diff line number Diff line
@@ -1291,6 +1291,7 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma, 
		goto out_unlock;



	page = pmd_page(pmd);

	BUG_ON(is_huge_zero_page(page));

	page_nid = page_to_nid(page);

	count_vm_numa_event(NUMA_HINT_FAULTS);

	if (page_nid == this_nid)
@@ -1481,8 +1482,15 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, 
		} else {

			struct page *page = pmd_page(*pmd);



			/* only check non-shared pages */

			/*

			 * Only check non-shared pages. Do not trap faults

			 * against the zero page. The read-only data is likely

			 * to be read-cached on the local CPU cache and it is

			 * less useful to know about local vs remote hits on

			 * the zero page.

			 */

			if (page_mapcount(page) == 1 &&

			    !is_huge_zero_page(page) &&

			    !pmd_numa(*pmd)) {

				entry = pmdp_get_and_clear(mm, addr, pmd);

				entry = pmd_mknuma(entry);

mm/memory.c

+1 −0
Original line number Diff line number Diff line
@@ -3564,6 +3564,7 @@ int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma, 
		pte_unmap_unlock(ptep, ptl);

		return 0;

	}

	BUG_ON(is_zero_pfn(page_to_pfn(page)));



	page_nid = page_to_nid(page);

	target_nid = numa_migrate_prep(page, vma, addr, page_nid);