From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754775Ab1DUQOV (ORCPT ); Thu, 21 Apr 2011 12:14:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36672 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750915Ab1DUQOU (ORCPT ); Thu, 21 Apr 2011 12:14:20 -0400 Date: Thu, 21 Apr 2011 18:14:02 +0200 From: Andrea Arcangeli To: Mel Gorman Cc: Minchan Kim , akpm@linux-foundation.org, raz ben yehuda , riel@redhat.com, kosaki.motohiro@jp.fujitsu.com, lkml , linux-mm@kvack.org, stable@kernel.org Subject: Re: [PATCH] mm: Check if PTE is already allocated during page fault Message-ID: <20110421161402.GS5611@random.random> References: <20110415101248.GB22688@suse.de> <20110421110841.GA612@suse.de> <20110421142636.GA1835@barrios-desktop> <20110421160057.GA28712@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110421160057.GA28712@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 21, 2011 at 05:00:57PM +0100, Mel Gorman wrote: > If you want to create a new patch with either your comment or mine > (whichever you prefer) I'll add my ack. I'm about to drop offline > for a few days but if it's still there Tuesday, I'll put together an > appropriate patch and submit. I'd keep it separate from the other patch > because it's a performance fix (which I'd like to see in -stable) where > as this is more of a cleanup IMO. I think the older patch should have more priority agreed. This one may actually waste cpu cycles overall, rather than saving them, it shouldn't be a common occurrence. >>From a code consistency point of view maybe we should just implement a pte_alloc macro (to put after pte_alloc_map) and use it in both places, and hide the glory details of the unlikely in the macro. When implementing pte_alloc, I suggest also adding unlikely to both, I mean we added unlikely to the fast path ok, but __pte_alloc is orders of magnitude less likely to fail than pte_none, and it still runs 1 every 512 4k page faults, so I think __pte_alloc deserves an unlikely too. Minchan, you suggested this cleanup, so I suggest you to send a patch, but if you're busy we can help. Thanks! Andrea