mm: numa: avoid unnecessary TLB flushes when setting NUMA hinting entries

Mel Gorman · torvalds · commit 10c1045f28e8 · 2015-02-12T18:54:08.000-08:00
If a PTE or PMD is already marked NUMA when scanning to mark entries for
NUMA hinting then it is not necessary to update the entry and incur a TLB
flush penalty.  Avoid the avoidhead where possible.

Signed-off-by: Mel Gorman &lt;mgorman@suse.de&gt;
Cc: Aneesh Kumar K.V &lt;aneesh.kumar@linux.vnet.ibm.com&gt;
Cc: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Cc: Dave Jones &lt;davej@redhat.com&gt;
Cc: Hugh Dickins &lt;hughd@google.com&gt;
Cc: Ingo Molnar &lt;mingo@redhat.com&gt;
Cc: Kirill Shutemov &lt;kirill.shutemov@linux.intel.com&gt;
Cc: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
Cc: Paul Mackerras &lt;paulus@samba.org&gt;
Cc: Rik van Riel &lt;riel@redhat.com&gt;
Cc: Sasha Levin &lt;sasha.levin@oracle.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
@@ -1493,12 +1493,14 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 			return 0;
 		}
 
-		ret = 1;
-		entry = pmdp_get_and_clear_notify(mm, addr, pmd);
-		entry = pmd_modify(entry, newprot);
-		ret = HPAGE_PMD_NR;
-		set_pmd_at(mm, addr, pmd, entry);
-		BUG_ON(pmd_write(entry));
+		if (!prot_numa || !pmd_protnone(*pmd)) {
+			ret = 1;
+			entry = pmdp_get_and_clear_notify(mm, addr, pmd);
+			entry = pmd_modify(entry, newprot);
+			ret = HPAGE_PMD_NR;
+			set_pmd_at(mm, addr, pmd, entry);
+			BUG_ON(pmd_write(entry));
+		}
 		spin_unlock(ptl);
 	}
 
diff --git a/mm/mprotect.c b/mm/mprotect.c
@@ -86,6 +86,10 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 				page = vm_normal_page(vma, addr, oldpte);
 				if (!page || PageKsm(page))
 					continue;
+
+				/* Avoid TLB flush if possible */
+				if (pte_protnone(oldpte))
+					continue;
 			}
 
 			ptent = ptep_modify_prot_start(mm, addr, pte);
