mm: numa: Trap pmd hinting faults only if we would otherwise trap PTE faults

Base page PMD faulting is meant to batch handle NUMA hinting faults from
PTEs. However, even is no PTE faults would ever be handled within a
range the kernel still traps PMD hinting faults. This patch avoids the
overhead.

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>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-37-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/mm/mprotect.c b/mm/mprotect.c
index f0b087d1069ce1cd5117bff5397523eab43f306f..5aae39017d6dd0af5385c04ef6c0b488900f6d8a 100644 (file)
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -146,6 +146,8 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 
        pmd = pmd_offset(pud, addr);
        do {
+               unsigned long this_pages;
+
                next = pmd_addr_end(addr, end);
                if (pmd_trans_huge(*pmd)) {
                        if (next - addr != HPAGE_PMD_SIZE)
@@ -165,8 +167,9 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                }
                if (pmd_none_or_clear_bad(pmd))
                        continue;
-               pages += change_pte_range(vma, pmd, addr, next, newprot,
+               this_pages = change_pte_range(vma, pmd, addr, next, newprot,
                                 dirty_accountable, prot_numa, &all_same_nidpid);
+               pages += this_pages;
 
                /*
                 * If we are changing protections for NUMA hinting faults then
@@ -174,7 +177,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                 * node. This allows a regular PMD to be handled as one fault
                 * and effectively batches the taking of the PTL
                 */
-               if (prot_numa && all_same_nidpid)
+               if (prot_numa && this_pages && all_same_nidpid)
                        change_pmd_protnuma(vma->vm_mm, addr, pmd);
        } while (pmd++, addr = next, addr != end);