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| author | Mel Gorman | 2013-10-07 12:28:50 +0200 |
|---|---|---|
| committer | Ingo Molnar | 2013-10-09 12:39:50 +0200 |
| commit | a1a46184e34cfd0764f06a54870defa052b0a094 (patch) | |
| tree | b4d12f1d23963fb3de14cf8d81f7979c4f58d95a /mm/huge_memory.c | |
| parent | mm: Only flush TLBs if a transhuge PMD is modified for NUMA pte scanning (diff) | |
| download | kernel-qcow2-linux-a1a46184e34cfd0764f06a54870defa052b0a094.tar.gz kernel-qcow2-linux-a1a46184e34cfd0764f06a54870defa052b0a094.tar.xz kernel-qcow2-linux-a1a46184e34cfd0764f06a54870defa052b0a094.zip | |
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.c | 10 |
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); |