From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 2 Mar 2007 00:21:49 -0800 (PST) From: Christoph Lameter Subject: Re: The performance and behaviour of the anti-fragmentation related patches In-Reply-To: <20070302081210.GD5557@wotan.suse.de> Message-ID: References: <20070302050625.GD15867@wotan.suse.de> <20070302054944.GE15867@wotan.suse.de> <20070302060831.GF15867@wotan.suse.de> <20070302062950.GG15867@wotan.suse.de> <20070302071955.GA5557@wotan.suse.de> <20070302081210.GD5557@wotan.suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Andrew Morton , Mel Gorman , mingo@elte.hu, jschopp@austin.ibm.com, arjan@infradead.org, torvalds@linux-foundation.org, mbligh@mbligh.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Fri, 2 Mar 2007, Nick Piggin wrote: > > If there are billions of pages in the system and we are allocating and > > deallocating then pages need to be aged. If there are just few pages > > freeable then we run into issues. > > page writeout and vmscan don't work too badly. What are the issues? Slow downs up to livelocks with large memory configurations. > So what problems that you commonly see now? Some of us here don't > have 4TB of memory, so you actually have to tell us ;) Oh just run a 32GB SMP system with sparsely freeable pages and lots of allocs and frees and you will see it too. F.e try Linus tree and mlock a large portion of the memory and then see the fun starting. See also Rik's list of pathological cases on this. > How did you come up with that 2MB number? Huge page size. The only basic choice on x86_64 > Anyway, we have hugetlbfs for things like that. Good to know that direct io works. > > I am not the first one.... See Rik's posts regarding the reasons for his > > new page replacement algorithms. > > Different issue, isn't it? Rik wants to be smarter in figuring out which > pages to throw away. More work per page == worse for you. Rik is trying to solve the same issue in a different way. He is trying to manage gazillion entries better instead of reducing the entries to be managed. That can only work in a limited way. Drastic reductions in the entries to be manages have good effects in multiple ways. Reduce management overhead, improve I/O throughput, etc etc. -- 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