linux-kernel - [PATCH 12/18] mm: numa: Defer TLB flush for THP migration as long as possible

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Date:	Mon,  9 Dec 2013 07:09:06 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alex Thorlton <athorlton@....com>, Rik van Riel <riel@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 12/18] mm: numa: Defer TLB flush for THP migration as long as possible

THP migration can fail for a variety of reasons. Avoid flushing the TLB
to deal with THP migration races until the copy is ready to start.

Cc: stable@...r.kernel.org
Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 mm/huge_memory.c | 7 -------
 mm/migrate.c     | 6 ++++++
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e3a5ee2..e3b6a75 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1377,13 +1377,6 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	}
 
 	/*
-	 * The page_table_lock above provides a memory barrier
-	 * with change_protection_range.
-	 */
-	if (tlb_flush_pending(mm))
-		flush_tlb_range(vma, haddr, haddr + HPAGE_PMD_SIZE);
-
-	/*
 	 * Migrate the THP to the requested node, returns with page unlocked
 	 * and pmd_numa cleared.
 	 */
diff --git a/mm/migrate.c b/mm/migrate.c
index cfb4190..5372521 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1759,6 +1759,12 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 		goto out_fail;
 	}
 
+	/* PTL provides a memory barrier with change_protection_range */
+	ptl = pmd_lock(mm, pmd);
+	if (tlb_flush_pending(mm))
+		flush_tlb_range(vma, mmun_start, mmun_end);
+	spin_unlock(ptl);
+
 	/* Prepare a page as a migration target */
 	__set_page_locked(new_page);
 	SetPageSwapBacked(new_page);
-- 
1.8.4

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