linux-kernel - Re: relatime: update once per day patches (was: ext3 IO latency measurements)

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Date:	Fri, 27 Mar 2009 06:25:15 -0500
From:	David Hagood <david.hagood@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Matthew Garrett <mjg@...hat.com>, Frans Pop <elendil@...net.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>, mingo@...e.hu,
	tytso@....edu, jack@...e.cz, alan@...rguk.ukuu.org.uk,
	arjan@...radead.org, a.p.zijlstra@...llo.nl, npiggin@...e.de,
	jens.axboe@...cle.com, drees76@...il.com, jesper@...gh.cc,
	linux-kernel@...r.kernel.org, oleg@...hat.com, roland@...hat.com
Subject: Re: relatime: update once per day patches (was: ext3 IO latency 
 measurements)

It seems to me that, rather than having the kernel maintain a timer (or
multiple timers, one per mount) itself, it would make sense to have
entries in /sys which, when written to, cause the file system layer to
flush all atime data to the mounted volume.

Something like
/sys
/sys/atime
/sys/atime/all
/sys/atime/<mountpoint id>/flush

where <mountpoint id> would be the name of the file system
(e.g. /sys/atime/usr/flush).

The only sticky part would be how to describe "/" in such a system.

(Better still would be a /sys/ system for each file system with the
various parameters (e.g. uid, journal) as entries + an entry for
flushing atime, but that is beyond the scope of this discussion.)

That would truly let userspace set policy, while the kernel provides
mechanism. Thus, a script that depends upon atime being accurate could
simply tickle the sysfs entries as needed before running.

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