From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx143.postini.com [74.125.245.143]) by kanga.kvack.org (Postfix) with SMTP id ED3C86B0005 for ; Mon, 18 Mar 2013 23:56:15 -0400 (EDT) Received: by mail-pd0-f177.google.com with SMTP id y14so18117pdi.8 for ; Mon, 18 Mar 2013 20:56:15 -0700 (PDT) Date: Mon, 18 Mar 2013 20:56:13 -0700 (PDT) From: David Rientjes Subject: Re: [patch] mm: speedup in __early_pfn_to_nid In-Reply-To: <20130318155619.GA18828@sgi.com> Message-ID: References: <20130318155619.GA18828@sgi.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Russ Anderson Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com On Mon, 18 Mar 2013, Russ Anderson wrote: > When booting on a large memory system, the kernel spends > considerable time in memmap_init_zone() setting up memory zones. > Analysis shows significant time spent in __early_pfn_to_nid(). > > The routine memmap_init_zone() checks each PFN to verify the > nid is valid. __early_pfn_to_nid() sequentially scans the list of > pfn ranges to find the right range and returns the nid. This does > not scale well. On a 4 TB (single rack) system there are 308 > memory ranges to scan. The higher the PFN the more time spent > sequentially spinning through memory ranges. > > Since memmap_init_zone() increments pfn, it will almost always be > looking for the same range as the previous pfn, so check that > range first. If it is in the same range, return that nid. > If not, scan the list as before. > > A 4 TB (single rack) UV1 system takes 512 seconds to get through > the zone code. This performance optimization reduces the time > by 189 seconds, a 36% improvement. > > A 2 TB (single rack) UV2 system goes from 212.7 seconds to 99.8 seconds, > a 112.9 second (53%) reduction. > > Signed-off-by: Russ Anderson Acked-by: David Rientjes Very nice improvement! -- 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