From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: Avoiding external fragmentation with a placement policy Version 12 From: Nick Piggin In-Reply-To: <429F2B26.9070509@austin.ibm.com> References: <20050531112048.D2511E57A@skynet.csn.ul.ie> <429E20B6.2000907@austin.ibm.com> <429E4023.2010308@yahoo.com.au> <423970000.1117668514@flay> <429E483D.8010106@yahoo.com.au> <434510000.1117670555@flay> <429E50B8.1060405@yahoo.com.au> <429F2B26.9070509@austin.ibm.com> Content-Type: text/plain Date: Fri, 03 Jun 2005 13:48:08 +1000 Message-Id: <1117770488.5084.25.camel@npiggin-nld.site> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: jschopp@austin.ibm.com Cc: "Martin J. Bligh" , Mel Gorman , linux-mm@kvack.org, lkml , Andrew Morton List-ID: On Thu, 2005-06-02 at 10:52 -0500, Joel Schopp wrote: > > I see your point... Mel's patch has failure cases though. > > For example, someone turns swap off, or mlocks some memory > > (I guess we then add the page migration defrag patch and > > problem is solved?). > > This reminds me that page migration defrag will be pretty useless > without something like this done first. There will be stuff that can't > be migrated and it needs to be grouped together somehow. > > In summary here are the reasons I see to run with Mel's patch: > > 1. It really helps with medium-large allocations under memory pressure. > 2. Page migration defrag will need it. > 3. Memory hotplug remove will need it. > I guess I'm now more convinced of its need ;) add: 4. large pages 5. (hopefully) helps with smaller allocations (ie. order 3) It would really help your cause in the short term if you can demonstrate improvements for say order-3 allocations (eg. use gige networking, TSO, jumbo frames, etc). > On the downside we have: > > 1. Slightly more complexity in the allocator. > For some definitions of 'slightly', perhaps :( Although I can't argue that a buddy allocator is no good without being able to satisfy higher order allocations. So in that case, I'm personally OK with it going into -mm. Hopefully there will be a bit more review and hopefully some simplification if possible. Last question: how does it go on systems with really tiny memories? (4MB, 8MB, that kind of thing). > I'd personally trade a little extra complexity for any of the 3 upsides. > -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com -- 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: aart@kvack.org