The patch titled Subject: mm, thp: move invariant bug check out of loop in __split_huge_page_map has been added to the -mm tree. Its filename is mm-thp-move-invariant-bug-check-out-of-loop-in-__split_huge_page_map.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-thp-move-invariant-bug-check-out-of-loop-in-__split_huge_page_map.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-move-invariant-bug-check-out-of-loop-in-__split_huge_page_map.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Waiman Long <Waiman.Long@xxxxxx> Subject: mm, thp: move invariant bug check out of loop in __split_huge_page_map 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> --- mm/huge_memory.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff -puN mm/huge_memory.c~mm-thp-move-invariant-bug-check-out-of-loop-in-__split_huge_page_map mm/huge_memory.c --- a/mm/huge_memory.c~mm-thp-move-invariant-bug-check-out-of-loop-in-__split_huge_page_map +++ a/mm/huge_memory.c @@ -1775,6 +1775,8 @@ 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) { @@ -1784,8 +1786,6 @@ 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 -mm which might be from Waiman.Long@xxxxxx are mm-thp-move-invariant-bug-check-out-of-loop-in-__split_huge_page_map.patch mm-thp-replace-smp_mb-after-atomic_add-by-smp_mb__after_atomic.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html