From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762867AbXHNWmT (ORCPT ); Tue, 14 Aug 2007 18:42:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752151AbXHNWl7 (ORCPT ); Tue, 14 Aug 2007 18:41:59 -0400 Received: from netops-testserver-4-out.sgi.com ([192.48.171.29]:39338 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753453AbXHNWly (ORCPT ); Tue, 14 Aug 2007 18:41:54 -0400 Date: Tue, 14 Aug 2007 15:41:53 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Andi Kleen cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c In-Reply-To: <20070814222150.GI23308@one.firstfloor.org> Message-ID: References: <20070814212355.GA23308@one.firstfloor.org> <20070814212955.GC23308@one.firstfloor.org> <20070814214430.GD23308@one.firstfloor.org> <20070814215659.GF23308@one.firstfloor.org> <20070814221616.GG23308@one.firstfloor.org> <20070814222150.GI23308@one.firstfloor.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 15 Aug 2007, Andi Kleen wrote: > > Ok I have a vague idea on how this could but its likely that the > > changes make things worse rather than better. Additional reference to a > > new cacheline (per cpu but still), preempt disable. Lots of code at all > > call sites. Interrupt enable/disable is quite efficient in recent > > processors. > > The goal of this was not to be faster than interrupt disable, > but to avoid the interrupt latency impact. This might be a problem > when spending a lot of time inside the locks. Both. They need to be fast too and not complicate the kernel too much. I have not seen a serious holdoff case. The biggest issue is still the zone->lru lock but interrupts are always disabled for that one already.