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 <[e-mail]>
Cc: Aneesh Kumar K.V <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: Dave Jones <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Kirill Shutemov <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Sasha Levin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/huge_memory.c

···
 			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);
 	}
 

mm/mprotect.c

···
 				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);