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authorMel Gorman <mgorman@suse.de>2013-10-07 11:28:50 +0100
committerIngo Molnar <mingo@kernel.org>2013-10-09 12:39:50 +0200
commita1a46184e34cfd0764f06a54870defa052b0a094 (patch)
treeb4d12f1d23963fb3de14cf8d81f7979c4f58d95a /mm/huge_memory.c
parentf123d74abf91574837d14e5ea58f6a779a387bf5 (diff)
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: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik 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: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1381141781-10992-13-git-send-email-mgorman@suse.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index de8d5cfc2bf2..8677dbf31c2e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -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);