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authorWaiman Long <Waiman.Long@hp.com>2014-08-06 23:05:36 (GMT)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-10-09 19:18:42 (GMT)
commit183c062c51c7e7663752b94ac399c830e4cb3c44 (patch)
tree669481eb67063f6be3257b68baad6026918bb8d5 /mm
parent78a3db11cb0e9521572c7d0effbc63f2bd5dac12 (diff)
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mm, thp: move invariant bug check out of loop in __split_huge_page_map
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@hp.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Scott J Norton <scott.norton@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/huge_memory.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index eb00e81..b9a096a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1733,6 +1733,8 @@ static int __split_huge_page_map(struct page *page,
if (pmd) {
pgtable = pgtable_trans_huge_withdraw(mm);
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) {
@@ -1742,8 +1744,6 @@ static int __split_huge_page_map(struct page *page,
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))