linux-kernel - [PATCH 10/10] mm: numa: Avoid unnecessary TLB flushes when setting NUMA hinting entries

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Date:	Mon,  5 Jan 2015 10:54:11 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LinuxPPC-dev <linuxppc-dev@...ts.ozlabs.org>,
	Mel Gorman <mgorman@...e.de>
Subject: [PATCH 10/10] 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@...e.de>
---
 mm/huge_memory.c | 14 ++++++++------
 mm/mprotect.c    |  4 ++++
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8546654..f2bf521 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1524,12 +1524,14 @@ 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 33dfafb..109e7aa 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);
-- 
2.1.2

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