This is a note to let you know that I've just added the patch titled
mm, thp: move invariant bug check out of loop in __split_huge_page_map
to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-thp-move-invariant-bug-check-out-of-loop-in-__split_huge_page_map.patch
and it can be found in the queue-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f8303c2582b889351e261ff18c4d8eb197a77db2 Mon Sep 17 00:00:00 2001
From: Waiman Long <Waiman.Long@xxxxxx>
Date: Wed, 6 Aug 2014 16:05:36 -0700
Subject: mm, thp: move invariant bug check out of loop in __split_huge_page_map
From: Waiman Long <Waiman.Long@xxxxxx>
commit f8303c2582b889351e261ff18c4d8eb197a77db2 upstream.
In __split_huge_page_map(), the check for page_mapcount(page) is
invariant within the for loop. Because of the fact that the macro is
implemented using atomic_read(), the redundant check cannot be optimized
away by the compiler leading to unnecessary read to the page structure.
This patch moves the invariant bug check out of the loop so that it will
be done only once. On a 3.16-rc1 based kernel, the execution time of a
microbenchmark that broke up 1000 transparent huge pages using munmap()
had an execution time of 38,245us and 38,548us with and without the
patch respectively. The performance gain is about 1%.
Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Scott J Norton <scott.norton@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1819,6 +1819,8 @@ static int __split_huge_page_map(struct
if (pmd) {
pgtable = pgtable_trans_huge_withdraw(mm, pmd);
pmd_populate(mm, &_pmd, pgtable);
+ if (pmd_write(*pmd))
+ BUG_ON(page_mapcount(page) != 1);
haddr = address;
for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
@@ -1828,8 +1830,6 @@ static int __split_huge_page_map(struct
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
if (!pmd_write(*pmd))
entry = pte_wrprotect(entry);
- else
- BUG_ON(page_mapcount(page) != 1);
if (!pmd_young(*pmd))
entry = pte_mkold(entry);
if (pmd_numa(*pmd))
Patches currently in stable-queue which might be from Waiman.Long@xxxxxx are
queue-3.14/mm-thp-move-invariant-bug-check-out-of-loop-in-__split_huge_page_map.patch
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