Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755933AbaFPUwa (ORCPT ); Mon, 16 Jun 2014 16:52:30 -0400 Received: from mta-out1.inet.fi ([62.71.2.198]:55674 "EHLO jenni2.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752582AbaFPUw2 (ORCPT ); Mon, 16 Jun 2014 16:52:28 -0400 Date: Mon, 16 Jun 2014 23:49:34 +0300 From: "Kirill A. Shutemov" To: Waiman Long Cc: Andrew Morton , Mel Gorman , Rik van Riel , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Scott J Norton Subject: Re: [PATCH] mm, thp: move invariant bug check out of loop in __split_huge_page_map Message-ID: <20140616204934.GA14208@node.dhcp.inet.fi> References: <1402947348-60655-1-git-send-email-Waiman.Long@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1402947348-60655-1-git-send-email-Waiman.Long@hp.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 16, 2014 at 03:35:48PM -0400, Waiman Long wrote: > 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. Looks okay, but why? Was you able to measure difference? -- Kirill A. Shutemov -- 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/