Subject: Re: UVM/other problems for desktop users in current?
To: Jukka Marin , Daniel Carosone <>
From: Daniel Carosone <>
List: current-users
Date: 12/18/2002 18:45:19
On Wed, Dec 18, 2002 at 09:37:52AM +0200, Jukka Marin wrote:
> But with the large RAM caches on the disk (like 8 MB in my case), can't
> the disk still do the actual (write) operations in an optimized order?

Yes, if you have write-cache on, those one-at-a-time transactions
will "complete" quickly.

It can't do that for reads, and so you might be asking the drive
to seek a lot more and further to fulfil a certain order of read
requests than it would have if it could reorder them first.

Plus the drive is unavailable while those seeks are going on, so the
next transaction can't be loaded in while the heads are moving.
That may actually be the greater penalty, assuming we hand the disk
reasonably well-ordered requests already.