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

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 <mgorman@suse.de>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 6 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8e07342b52c0..fc00c8cb5a82 100644
--- 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);
 	}