Re: [RFC] Limit the size of the pagecache

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Thu, 25 Jan 2007 00:40:54 -0500
Rik van Riel <riel@redhat.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > On Wed, 24 Jan 2007 23:28:15 -0500
> > Rik van Riel <riel@redhat.com> wrote:
> > 
> >> KAMEZAWA Hiroyuki wrote:
> > I always says Linux is different from mainframes.
> 
> It's not just about Linux.
> 
> Applications behave differently too from the way they were 15
> years ago.
> 
> Some databases, eg. sleepycat's db, map the whole database in
> memory.  Other databases, like MySQL and postgresql, rely on
> the kernel's page cache to cache the most frequently accessed
> data.
> 
> To make matters more interesting, memory sizes have increased
> by a factor 1000, but disk seek times have only gotten 10 times
> faster.  This means that simplistic memory management algorithms
> can hurt performance a lot more than they could back then.
> 
> In short, I am not convinced that any of the simple tunable knobs
> from the "good old days" will do much to actually help people
> with modern workloads on modern computers.
> 
I agree. 

My current concerns is not adding knobs but how to show/explain
what the users does. In most case, users don't know what they does
and believes system-information can tell that.

for example)
A user sometimes asks "why amount of system-A's pagecache and system-B's are
different from each other ?. I definitly does the same jobs on the both system."

...just because he used different deta-set ;)

Thanks,
-Kame


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