From mboxrd@z Thu Jan 1 00:00:00 1970 From: Carsten Otte Subject: Re: [RFC/PATCH 0/5] add execute in place support Date: Wed, 11 May 2005 18:35:28 +0200 Message-ID: <42823450.8030007@freenet.de> References: <428216DF.8070205@de.ibm.com> <1115828389.16187.544.camel@hades.cambridge.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, schwidefsky@de.ibm.com, akpm@osdl.org Return-path: Received: from mtagate4.de.ibm.com ([195.212.29.153]:15817 "EHLO mtagate4.de.ibm.com") by vger.kernel.org with ESMTP id S261978AbVEKQfe (ORCPT ); Wed, 11 May 2005 12:35:34 -0400 To: David Woodhouse In-Reply-To: <1115828389.16187.544.camel@hades.cambridge.redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org David Woodhouse wrote: >On Wed, 2005-05-11 at 16:29 +0200, Carsten Otte wrote: > > >>. This is also useful on embedded systems where the block device is >>located on a flash chip. >> >> > >On Wed, 2005-05-11 at 17:33 +0200, Carsten Otte wrote: > > >>Indeed that seems reasonable. There is no exact reason to have >>this built into a kernel on a platform that does not have a bdev >>for this. >> >> > >The sanest way to use flash chips is not to pretend that they're a block >device at all; rather to use a file system directly on top of them. > >But although you _talk_ about block devices, your code does look like it >should be usable even by flash file systems. I'll try to come up with a >test case using it on flash. > > > Yes and no. For execute in place to work proper, you need an allignment of data to page boundaries "on disk" (or on flash) just like you have when mmap()ing to userland. Before choosing second extended, I also looked at some flash/rom filesystems. But I was unable to identify one that alligns the data proper (and does not compress things or such). The ext family with block size == PAGE_SIZE does fullfill that requirement once the "block device" starts on page boundary. On the other hand I believe that a filesystem specificaly designed for flash can provide less metadata overhead then second extended. Would also be interresting in our use-case on s390.