From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 139316B004D for ; Tue, 18 Aug 2009 09:10:21 -0400 (EDT) Date: Tue, 18 Aug 2009 14:10:24 +0100 From: Mel Gorman Subject: Re: [PATCH 1/3] page-allocator: Split per-cpu list into one-list-per-migrate-type Message-ID: <20090818131024.GD31469@csn.ul.ie> References: <1250594162-17322-1-git-send-email-mel@csn.ul.ie> <1250594162-17322-2-git-send-email-mel@csn.ul.ie> <20090818114335.GO9962@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20090818114335.GO9962@wotan.suse.de> Sender: owner-linux-mm@kvack.org To: Nick Piggin Cc: Linux Memory Management List , Christoph Lameter , Linux Kernel Mailing List List-ID: On Tue, Aug 18, 2009 at 01:43:35PM +0200, Nick Piggin wrote: > On Tue, Aug 18, 2009 at 12:16:00PM +0100, Mel Gorman wrote: > > Currently the per-cpu page allocator searches the PCP list for pages of the > > correct migrate-type to reduce the possibility of pages being inappropriate > > placed from a fragmentation perspective. This search is potentially expensive > > in a fast-path and undesirable. Splitting the per-cpu list into multiple > > lists increases the size of a per-cpu structure and this was potentially > > a major problem at the time the search was introduced. These problem has > > been mitigated as now only the necessary number of structures is allocated > > for the running system. > > > > This patch replaces a list search in the per-cpu allocator with one list per > > migrate type. The potential snag with this approach is when bulk freeing > > pages. We round-robin free pages based on migrate type which has little > > bearing on the cache hotness of the page and potentially checks empty lists > > repeatedly in the event the majority of PCP pages are of one type. > > Seems OK I guess. Trading off icache and branches for dcache and > algorithmic gains. Too bad everything is always a tradeoff ;) > Tell me about it. The dcache overhead of this is a problem although I tried to limit the damage using pahole to see how much padding I had to play with and staying within it where possible. > But no I think this is a good idea. > Thanks. Is that an Ack? > > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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