From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 2A9476B01E3 for ; Mon, 12 Apr 2010 09:34:55 -0400 (EDT) Message-ID: <4BC3213E.40409@redhat.com> Date: Mon, 12 Apr 2010 16:33:50 +0300 From: Avi Kivity MIME-Version: 1.0 Subject: Re: hugepages will matter more in the future References: <4BC0E2C4.8090101@redhat.com> <4BC0E556.30304@redhat.com> <4BC19663.8080001@redhat.com> <4BC19916.20100@redhat.com> <20100411110015.GA10149@elte.hu> <4BC1B034.4050302@redhat.com> <20100411115229.GB10952@elte.hu> <20100412042230.5d974e5d@infradead.org> <20100412133019.GZ5656@random.random> In-Reply-To: <20100412133019.GZ5656@random.random> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Andrea Arcangeli Cc: Arjan van de Ven , Ingo Molnar , Jason Garrett-Glaser , Mike Galbraith , Linus Torvalds , Pekka Enberg , Andrew Morton , linux-mm@kvack.org, Marcelo Tosatti , Adam Litke , Izik Eidus , Hugh Dickins , Nick Piggin , Rik van Riel , Mel Gorman , Dave Hansen , Benjamin Herrenschmidt , Mike Travis , KAMEZAWA Hiroyuki , Christoph Lameter , Chris Wright , bpicco@redhat.com, KOSAKI Motohiro , Balbir Singh , Arnd Bergmann , "Michael S. Tsirkin" , Peter Zijlstra , Johannes Weiner , Daisuke Nishimura List-ID: On 04/12/2010 04:30 PM, Andrea Arcangeli wrote: > On Mon, Apr 12, 2010 at 04:22:30AM -0700, Arjan van de Ven wrote: > >> Now hugepages have some interesting other advantages, namely they save >> pagetable memory..which for something like TPC-C on a fork based >> database can be a measureable win. >> > It doesn't save pagetable memory (as in `grep MemFree > /proc/meminfo`). So where does the pagetable go? > To achive that we'd need to return -ENOMEM from > split_huge_page_pmd and split_huge_page, which would complicate things > significantly. I'd prefer if we could get rid gradually of > split_huge_page_pmd calls instead of having to handle a retval in > several inner nested functions that don't contemplate returning error > like all their callers. > > I think the saving in pagetables isn't really interesting... it's a > couple of gigabytes but it doesn't move the needle as much as being > able to boost CPU performance. > Fork-based (or process+shm based, like Oracle) replicate the page tables per process, so it's N * 0.2%, which would be quite large. We could share pmds for large shared memory areas, but it wouldn't be easy. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- 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