From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264673AbUE0RYL (ORCPT ); Thu, 27 May 2004 13:24:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264725AbUE0RYL (ORCPT ); Thu, 27 May 2004 13:24:11 -0400 Received: from sccrmhc11.comcast.net ([204.127.202.55]:3309 "EHLO sccrmhc11.comcast.net") by vger.kernel.org with ESMTP id S264706AbUE0RXs (ORCPT ); Thu, 27 May 2004 13:23:48 -0400 From: "Buddy Lumpkin" To: "'Nick Piggin'" Cc: "'John Bradford'" , "'William Lee Irwin III'" , , Subject: RE: why swap at all? Date: Thu, 27 May 2004 10:27:01 -0700 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Office Outlook, Build 11.0.5510 In-Reply-To: <40B57E9D.8020606@yahoo.com.au> X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 Thread-Index: AcRDrLj5Txp/vOOeQNuPZmniDuQ7pgAEIMSw Message-Id: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org >I can picture it but I don't know how the kernel is going to handle >it. All I am doing is speaking from what I have seen. >http://marc.theaimsgroup.com/?l=linux-kernel&m=107817776322044&w=2 >This post for example, has profiles of a 32 CPU system with 16 FC >controllers and over 1000 disks, doing some database workload. Does >this qualify as big iron? >In the bottom profile, you see the disks being kept busy with 50% >idle time. The top 6 functions are all to do with generating IO >requests and pushing them through the block layer, none of them >involve memory reclaim. They are using direct I/O ... therefore the DMA memory transfers are mapped directly into the user address space bypassing the pagecache altogether. --Buddy There are profiles from a different setup in a related thread here: http://groups.google.com.au/groups?q=g:thl3816668183d&dq=&hl=en&lr=&ie=UTF-8 &selm=1yjKu-7qU-1%40gated-at.bofh.it&rnum=9 I think we see kmem_cache_alloc make a miserable showing for the memory allocation team, but it wouldn't even be there if the profile were sorted by ticks (the left hand column). Now If you had some experiences of memory reclaim slowing down block IO, I'd love to hear them because that is related to an area that I am looking at currently. I'm not saying what you claim is impossible, but it is something that shouldn't happen and we don't relly see... You're continuing to insist there is a problem but that simply isn't helpful without further details.