Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH] mm, thp: move invariant bug check out of loop in __split_huge_page_map | Date | Mon, 16 Jun 2014 15:35:48 -0400 |
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In the __split_huge_page_map() function, 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 move the invariant bug check out of the loop so that it will be done only once.
Signed-off-by: Waiman Long <Waiman.Long@hp.com> --- mm/huge_memory.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index b4b1feb..b8bb16c 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1744,6 +1744,8 @@ static int __split_huge_page_map(struct page *page, 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) { @@ -1753,8 +1755,6 @@ 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)) -- 1.7.1
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