Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932196AbWC1UpQ (ORCPT ); Tue, 28 Mar 2006 15:45:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932198AbWC1UpQ (ORCPT ); Tue, 28 Mar 2006 15:45:16 -0500 Received: from cantor2.suse.de ([195.135.220.15]:17611 "EHLO mx2.suse.de") by vger.kernel.org with ESMTP id S932196AbWC1UpO (ORCPT ); Tue, 28 Mar 2006 15:45:14 -0500 From: Andi Kleen To: "Frank Ch. Eigler" Subject: Re: RFC - Approaches to user-space probes Date: Tue, 28 Mar 2006 22:44:47 +0200 User-Agent: KMail/1.9.1 Cc: prasanna@in.ibm.com, Arjan van de Ven , Andrew Morton , davem@davemloft.net, suparna@in.ibm.com, richardj_moore@uk.ibm.com, linux-kernel@vger.kernel.org, Christoph Hellwig , "Theodore Ts'o" , Nick Piggin References: <20060327065447.GA25745@in.ibm.com> <20060328145441.GA25465@in.ibm.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200603282244.48900.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1261 Lines: 31 On Tuesday 28 March 2006 22:35, Frank Ch. Eigler wrote: > Prasanna S Panchamukhi writes: > > > [...] > > If the executable is mmaped shared, then those mappings will get written > > back to the disk. > > Writting to the disk is not the requirement for user-space probes, it is > > just the side effect [...] > > It's pretty clear that writing the dirtied pages to disk is an > *undesirable* side-effect, and should be eliminated. (Among many > other scenarios, imagine a kernel shutting down without all the probes > being cleanly removed. Then the executables are irretrievably > corrupted.) That's pretty hard unfortunately. There are plenty of operations that just access the page cache directly for IO (like sendfile or mmap or other IO) And allocating bounce buffers is tricky because the IO paths cannot allocate memory reliably without deadlocks (or rather it would require mempool and other inefficient measures) Doing forced COW like ptrace is probably more practical. -Andi - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/