Re: ext3 IO latency measurements (was: Linux 2.6.29)

Matthew Garrett
2009-03-26T20:04:20Z

On Thu, Mar 26, 2009 at 06:59:00PM +0000, Alan Cox wrote:
> > And what's the argument for not doing it in the kernel?
> >
> > The fact is, "atime" by default is just wrong.
>
> It probably was a wrong default - twenty years ago. Actually it may well
> have been a wrong default in Unix v6 8)
>
> However
> - atime behaviour is SuS required

SuS says "An implementation may update fields that are marked for update
immediately, or it may update such fields periodically. At an update
point in time, any marked fields shall be set to the current time and
the update marks shall be cleared" but doesn't appear to specify any
kind of time limit. A conforming implementation could wait a century
before performing the update. So while relatime doesn't conform, the
practical difference is meaningless. You can't depend on atime being
updated in a timely manner.

--
Matthew Garrett | mjg59@srcf.ucam.org