From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com [9.17.195.106]) by e33.co.us.ibm.com (8.12.11/8.12.11) with ESMTP id jB1IPn2V002631 for ; Thu, 1 Dec 2005 13:25:49 -0500 Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay04.boulder.ibm.com (8.12.10/NCO/VERS6.8) with ESMTP id jB1IRI5F086892 for ; Thu, 1 Dec 2005 11:27:18 -0700 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.12.11/8.13.3) with ESMTP id jB1IPmP4026977 for ; Thu, 1 Dec 2005 11:25:48 -0700 Subject: Re: Better pagecache statistics ? From: Badari Pulavarty In-Reply-To: <20051201181525.GB17169@dmt.cnet> References: <1133377029.27824.90.camel@localhost.localdomain> <20051201152029.GA14499@dmt.cnet> <1133452790.27824.117.camel@localhost.localdomain> <20051201171938.GB16235@dmt.cnet> <1133458309.21429.36.camel@localhost.localdomain> <20051201181525.GB17169@dmt.cnet> Content-Type: text/plain Date: Thu, 01 Dec 2005 10:25:59 -0800 Message-Id: <1133461559.21429.54.camel@localhost.localdomain> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Marcelo Tosatti Cc: linux-mm , lkml List-ID: On Thu, 2005-12-01 at 16:15 -0200, Marcelo Tosatti wrote: > > > I thought that it would be easy to use SystemTap for a such > > > a purpose? > > > > > > The sys_read/sys_write example at > > > http://www.redhat.com/magazine/011sep05/features/systemtap/ sounds > > > interesting. > > > > > > What I'm I missing? > > > > Well, Few things: > > > > 1) We have to have those probes present in the system all the time > > collecting the information when read/write happens, maintaining it > > and spitting it out. Since its kernel probe, all this data will be > > in the kernel. > > Yeah, there is some overhead. > > > 2) If we want to do this accounting (and you don't have those probes > > installed already) - we can't capture what happened earlier. > > I suppose that the vast majority of situations where such information is > needed are special anyway? > > Why do you need it around all the time? Otherwise, we need to insert hooks and ask the customer to reproduce the problem :( > > 3) probing sys_read/sys_write() are going to tell you how much > > a data a process did read or wrote - but its not going to tell you > > how much is in the cache (now or 10 minutes later). > > Sure, that was just an example - need to insert probes > on the correct places. Okay, I miss understood. Thanks, Badari -- 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