From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: recursive mtime patches Date: Thu, 14 Apr 2011 11:21:17 +0200 Message-ID: <20110414092117.GB5054@quack.suse.cz> References: <20110412154830.GF5246@quack.suse.cz> <20110413213937.GB4648@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Jan Kara , Ext4 Developers List To: Amir Goldstein Return-path: Received: from cantor.suse.de ([195.135.220.2]:35753 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757353Ab1DNJVT (ORCPT ); Thu, 14 Apr 2011 05:21:19 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu 14-04-11 10:12:26, Amir Goldstein wrote: > On Thu, Apr 14, 2011 at 12:39 AM, Jan Kara wrote: > > On Wed 13-04-11 21:16:40, Amir Goldstein wrote: > >> On Tue, Apr 12, 2011 at 5:48 PM, Jan Kara wrote: > >> > modification stamps have possibly larger race windows but I have= n't really > >> > tried how much (I just know that even mtime races are not that h= ard to > >> > trigger if you try). So it really depends on how big reliability= do you > >> > expect and I personally don't find much value in just rescanning= and > >> > checking for mtime after a crash. Reading all the data and doing= checksum > >> > certainly has more value but at a high cost. > >> > > >> > >> What do you thing about the approach to store recursively modified= dir inodes in > >> a journal "modified inode descriptor block" and update the recursi= ve mtime of > >> those dirs on journal recovery? > > =A0The trouble is you don't know the number of directories that may= need > > to have timestamp updated - you find that out only as you travel up= wards. > > So it's hard to reserve any fixed space for this. > > >=20 > True, but you can save *so* many inode numbers in just one descriptor > block and in case of an overflow, we can just pass a hint to the top > level application to do a full directory scan, so I hardly see that a= s a > big problem. Well, about 1000 but you can still have about 8000 inodes modified in= a transaction for a standard 128 MB journal. You can notify the userspace when an overflow happens but the interface gets kind of ugly... Also it would be only specific to ext3/4 while I'd prefer to get a wider fs support. > >> I would also consider to use a mount option rec_mtime and then jus= t > >> store recursive > >> mtime in the directory's inode mtime instead of an extended attrib= ute. > >> That doesn't break any contract with user space, it's just a re-in= terpretation > >> of the dir modification notion. > > =A0It breaks POSIX specification - POSIX pretty much specifies when= mtime is > > supposed to be changed - so I'm not sure we really want to do that.= =2E. >=20 > I disagree, POSIX doesn't forbid a user space daemon from touching di= rectory > inodes and updating their mtime. The rec_mtime feature should be trea= ted as > a little kernel "daemon" which propagates information to user space b= y touching > recursively modified directories. OK, if you look at it this way it makes some sense. You loose the distinction whether something has been created / deleted in the directo= ry or whether only something happened in its subdirectory or file but that does not seem too important for any use case I can think of. Honza --=20 Jan Kara SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html