Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755897AbaJGXiX (ORCPT ); Tue, 7 Oct 2014 19:38:23 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:39595 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755521AbaJGXTx (ORCPT ); Tue, 7 Oct 2014 19:19:53 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Waiman Long , "Kirill A. Shutemov" , Andrea Arcangeli , Mel Gorman , Rik van Riel , Scott J Norton , Andrew Morton , Linus Torvalds Subject: [PATCH 3.16 23/26] mm, thp: move invariant bug check out of loop in __split_huge_page_map Date: Tue, 7 Oct 2014 16:19:39 -0700 Message-Id: <20141007231849.168289729@linuxfoundation.org> X-Mailer: git-send-email 2.1.2 In-Reply-To: <20141007231848.487609292@linuxfoundation.org> References: <20141007231848.487609292@linuxfoundation.org> User-Agent: quilt/0.63-1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: Waiman Long 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 Acked-by: Kirill A. Shutemov Cc: Andrea Arcangeli Cc: Mel Gorman Cc: Rik van Riel Cc: Scott J Norton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/huge_memory.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/huge_memory.c +++ b/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)) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/