From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-bk0-f54.google.com (mail-bk0-f54.google.com [209.85.214.54]) by kanga.kvack.org (Postfix) with ESMTP id B99FD6B0031 for ; Wed, 8 Jan 2014 13:26:58 -0500 (EST) Received: by mail-bk0-f54.google.com with SMTP id v16so792869bkz.41 for ; Wed, 08 Jan 2014 10:26:58 -0800 (PST) Received: from mail-bk0-x232.google.com (mail-bk0-x232.google.com [2a00:1450:4008:c01::232]) by mx.google.com with ESMTPS id o5si590871bkr.56.2014.01.08.10.26.57 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 08 Jan 2014 10:26:57 -0800 (PST) Received: by mail-bk0-f50.google.com with SMTP id e11so786079bkh.23 for ; Wed, 08 Jan 2014 10:26:57 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20140108111640.GD8256@quack.suse.cz> References: <20140107122301.GC16640@quack.suse.cz> <20140108111640.GD8256@quack.suse.cz> Date: Wed, 8 Jan 2014 23:56:57 +0530 Message-ID: Subject: Re: [LSF/MM ATTEND] Stackable Union Filesystem Implementation From: Saket Sinha Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Jan Kara Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, lsf-pc@lists.linux-foundation.org >> One of the big problems was that too many copyups were made on the >> read-write file system. So we decided to implement an union file >> system designed for diskless systems, with the following >> functionalities: >> >> 1. union between only one read-only and one read-write file systems >> >> 2. if only the file metadata are modified, then do not >> copy the whole file on the read-write files system but >> only the metadata (stored with a file named as the file >> itself prefixed by '.me.') > So do you do anything special at CERN so that metadata is often modified > without data being changed? Because there are only two operations where I > can imagine this to be useful: > 1) atime update - but you better turn atime off for unioned filesystem > anyway. > 2) xattr update > As already mentioned that the issue that we were facing was that "too many copyups were made on the read-write file system". Writes to a file system in a unioning file system will produce many duplicated blocks in memory since it uses a stackable filesystem approach so response time for a particular operation is also a concern. Regards, Saket Sinha -- 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