From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f178.google.com (mail-we0-f178.google.com [74.125.82.178]) by kanga.kvack.org (Postfix) with ESMTP id 615466B0031 for ; Mon, 16 Jun 2014 16:52:24 -0400 (EDT) Received: by mail-we0-f178.google.com with SMTP id x48so5596588wes.9 for ; Mon, 16 Jun 2014 13:52:23 -0700 (PDT) Received: from jenni2.inet.fi (mta-out1.inet.fi. [62.71.2.198]) by mx.google.com with ESMTP id d11si10011355wic.34.2014.06.16.13.52.22 for ; Mon, 16 Jun 2014 13:52:22 -0700 (PDT) Date: Mon, 16 Jun 2014 23:49:34 +0300 From: "Kirill A. Shutemov" 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org