linux-kernel - Re: [PATCH 00/23] per device dirty throttling -v8

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Message-Id: <1186336878.2777.15.camel@laptopd505.fenrus.org>
Date:	Sun, 05 Aug 2007 11:01:18 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Theodore Tso <tytso@....edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jörn Engel <joern@...fs.org>,
	Ingo Molnar <mingo@...e.hu>, Jeff Garzik <jeff@...zik.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	miklos@...redi.hu, akpm@...ux-foundation.org, neilb@...e.de,
	dgc@....com, tomoki.sekiyama.qu@...achi.com, nikita@...sterfs.com,
	trond.myklebust@....uio.no, yingchao.zhou@...il.com,
	richard@....demon.co.uk, david@...g.hm
Subject: Re: [PATCH 00/23] per device dirty throttling -v8

On Sat, 2007-08-04 at 17:48 -0400, Theodore Tso wrote:
> On Sat, Aug 04, 2007 at 01:13:19PM -0700, Arjan van de Ven wrote:
> > there is another trick possible (more involved though, Al will have to
> > jump in on that one I suspect): Have 2 types of "dirty inode" states;
> > one is the current dirty state (meaning the full range of ext3
> > transactions etc) and "lighter" state of "atime-dirty"; which will not
> > do the background syncs or journal transactions (so if your machine
> > crashes, you lose the atime update) but it does keep atime for most
> > normal cases and keeps it standard compliant "except after a crash".
> 
> That would make us standards compliant (POSIX explicitly says that
> what happens after a unclean shutdown is Unspecified) and it would
> make things a heck of a lot faster.  However, there is a potential
> problem which is that it will keep a large number of inodes pinned in
> memory, which is its own problem.  So there would have to be some way
> to force the atime updates to be merged when under memory pressure,
> and and perhaps on some much longer background interval (i.e., every
> hour or so).

on the journalling side this would be one transaction (not 5 milion)
and... since inodes are grouped on disk, you can even get some better
coalescing this way... 

Wonder if we could do inode-grouping smartly; eg if we HAVE to write
inode X, also write out the atime-dirty inodes in range X-Y to X+Y
(where Y is some tunable) in the same IO..


-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

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