linux-kernel - [PATCH] mm: Flush the TLB for a single address in a huge page

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Date:	Wed, 22 Jul 2015 18:13:34 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: [PATCH] mm: Flush the TLB for a single address in a huge page

When the page table entry is a huge page (and not a table), there is no
need to flush the TLB by range. This patch changes flush_tlb_range() to
flush_tlb_page() in functions where we know the pmd entry is a huge
page.

Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andrea Arcangeli <aarcange@...hat.com>
---

Hi,

That's just a minor improvement but it saves iterating over each small
page in a huge page when a single TLB entry is used (we already have a
similar assumption in __tlb_adjust_range).

Thanks.

 mm/pgtable-generic.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index 6b674e00153c..ff17eca26211 100644
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -67,7 +67,7 @@ int pmdp_set_access_flags(struct vm_area_struct *vma,
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 	if (changed) {
 		set_pmd_at(vma->vm_mm, address, pmdp, entry);
-		flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
+		flush_tlb_page(vma, address);
 	}
 	return changed;
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
@@ -101,7 +101,7 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 	young = pmdp_test_and_clear_young(vma, address, pmdp);
 	if (young)
-		flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
+		flush_tlb_page(vma, address);
 	return young;
 }
 #endif
@@ -128,7 +128,7 @@ pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 	VM_BUG_ON(!pmd_trans_huge(*pmdp));
 	pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
-	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
+	flush_tlb_page(vma, address);
 	return pmd;
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
@@ -143,7 +143,7 @@ void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 	set_pmd_at(vma->vm_mm, address, pmdp, pmd);
 	/* tlb flush only to serialize against gup-fast */
-	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
+	flush_tlb_page(vma, address);
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
@@ -195,7 +195,7 @@ void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
 {
 	pmd_t entry = *pmdp;
 	set_pmd_at(vma->vm_mm, address, pmdp, pmd_mknotpresent(entry));
-	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
+	flush_tlb_page(vma, address);
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
--
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