Re: block cache replacement strategy?

[Johannes Stezenbach]

On Tue, Sep 14, 2010 at 05:09:31AM +1000, dave b wrote:
> On 14 September 2010 01:21, Johannes Stezenbach <js@xxxxxxxxx> wrote:
> > On Fri, Sep 10, 2010 at 06:02:48PM +0200, Johannes Stezenbach wrote:
> >>
> >> Linear read heuristic might be a good guess, but it would
> >> be nice to hear a comment from a vm/fs expert which
> >> confirms this works as intended.
> >
> > Anyway I found lmdd (from lmbench) can do random reads,
> > and indeed causes the data to enter the block (page?) cache,
> > replacing the previous data.
> 
> I am no expert, but what did you think would happen if you did dd
> twice from /dev/zero?
> but... Honestly what do you think will be cached?

It's not from /dev/zero, it is from file to /dev/null.

It all started with me wanting to compare disk read bandwidth
vs. read bandwidth of my root partition via dm-crypt + LVM,
and then wondering why dd from raw disk seemed to be
cached while dd from crypted root partition didn't.


Johannes
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