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>

2 files changed, 12 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);
         }
 
diff --git a/mm/mprotect.c b/mm/mprotect.c
index dd599fc235c2..44727811bf4c 100644
--- 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);