[PATCH 35/50] mm: numa: Only trap pmd hinting faults if we would otherwise trap PTE faults

[Mel Gorman]

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@xxxxxxx>
---
 mm/mprotect.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 70ec934..191a89a 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -154,6 +154,8 @@ 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)
@@ -173,8 +175,9 @@ 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
@@ -182,7 +185,7 @@ 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);
 
-- 
1.8.1.4

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