From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id D71498D0039 for ; Fri, 25 Feb 2011 19:16:50 -0500 (EST) Date: Sat, 26 Feb 2011 01:16:11 +0100 From: Andrea Arcangeli Subject: Re: [PATCH 2/2] mm: compaction: Minimise the time IRQs are disabled while isolating pages for migration Message-ID: <20110226001611.GA19630@random.random> References: <1298664299-10270-1-git-send-email-mel@csn.ul.ie> <1298664299-10270-3-git-send-email-mel@csn.ul.ie> <20110225223204.GW25382@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110225223204.GW25382@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Mel Gorman , Andrew Morton , Arthur Marsh , Clemens Ladisch , Linux-MM , Linux Kernel Mailing List On Fri, Feb 25, 2011 at 11:32:04PM +0100, Johannes Weiner wrote: > I don't understand why this conditional is broken up like this. > cond_resched() will have the right checks anyway. Okay, you would > save fatal_signal_pending() in the 'did one cluster' case. Is it that > expensive? Couldn't this be simpler like > > did_cluster = ((low_pfn + 1) % SWAP_CLUSTER_MAX) == 0 > lock_contended = spin_is_contended(&zone->lru_lock); > if (did_cluster || lock_contended || need_resched()) { > spin_unlock_irq(&zone->lru_lock); > cond_resched(); > spin_lock_irq(&zone->lru_lock); > if (fatal_signal_pending(current)) > break; > } > > instead? If we don't release irqs first, how can need_resched get set in the first place if the local apic irq can't run? I guess that's why there's no cond_resched_lock_irq. BTW, I never liked too much clearing interrupts for locks that can't ever be taken from irq (it's a scalability boost to reduce contention but it makes things like above confusing and it increases irq latency a bit. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org