Subject: Re: disk caching
To: Thor Lancelot Simon <firstname.lastname@example.org>
From: Manuel Bouyer <email@example.com>
Date: 04/14/2000 11:42:12
On Thu, Apr 13, 2000 at 10:49:19PM -0400, Thor Lancelot Simon wrote:
> Actually, that's not quite right. We have the old "sprite" interval
> flush policy: we flush all buffers -- pages, eventually? -- for a file
> when the oldest buffer in that file hits 30 seconds.
> This is *not* the same as the policy generally considered to be correct
> since the Mogul paper: flush each buffer when it hits 30 seconds of age.
> There are some very common cases which are pathological for the algorithm
> we have in that its performance degrades to that of the old "flush all
> buffers every 30 seconds of wall-clock time" method. For example, if
> you have a system that does most of its I/O to a single file... you lose.
Then maybe we need 2 separate buffer queues, one for background flushs
and one for "urgent" I/O (reads, sync writes, ...) ?
Manuel Bouyer, LIP6, Universite Paris VI. Manuel.Bouyer@lip6.fr