From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751500AbZEOLVh (ORCPT ); Fri, 15 May 2009 07:21:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752476AbZEOLV1 (ORCPT ); Fri, 15 May 2009 07:21:27 -0400 Received: from one.firstfloor.org ([213.235.205.2]:53504 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751876AbZEOLV1 (ORCPT ); Fri, 15 May 2009 07:21:27 -0400 Date: Fri, 15 May 2009 13:26:56 +0200 From: Andi Kleen To: =?utf-8?Q?Micha=C5=82?= Nazarewicz Cc: Andi Kleen , Peter Zijlstra , Andrew Morton , linux-kernel@vger.kernel.org, m.szyprowski@samsung.com, kyungmin.park@samsung.com, linux-mm@kvack.org Subject: Re: [PATCH] Physical Memory Management [0/1] Message-ID: <20090515112656.GD16682@one.firstfloor.org> References: <1242300002.6642.1091.camel@laptop> <1242302702.6642.1140.camel@laptop> <20090514100718.d8c20b64.akpm@linux-foundation.org> <1242321000.6642.1456.camel@laptop> <20090515101811.GC16682@one.firstfloor.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 15, 2009 at 12:47:23PM +0200, Michał Nazarewicz wrote: > On Fri, 15 May 2009 12:18:11 +0200, Andi Kleen wrote: > > That's not correct, support for multiple huge page sizes was recently > > added. The interface is a bit clumpsy admittedly, but it's there. > > I'll have to look into that further then. Having said that, I cannot > create a huge page SysV shared memory segment with pages of specified > size, can I? sysv shared memory supports huge pages, but there is currently no interface to specify the intended page size, you always get the default. > > > However for non fragmentation purposes you probably don't > > want too many different sizes anyways, the more sizes, the worse > > the fragmentation. Ideal is only a single size. > > Unfortunately, sizes may very from several KiBs to a few MiBs. Then your approach will likely not be reliable. > On the other hand, only a handful of apps will use PMM in our system > and at most two or three will be run at the same time so hopefully > fragmentation won't be so bad. But yes, I admit it is a concern. Such tight restrictions might work for you, but for mainline Linux the quality standards are higher. > > As Peter et.al. explained earlier varying buffer sizes don't work > > anyways. > > Either I missed something or Peter and Adrew only pointed the problem > we all seem to agree exists: a problem of fragmentation. Multiple buffer sizes lead to fragmentation. -Andi -- ak@linux.intel.com -- Speaking for myself only.