Re: cache limit

[Nick Piggin <piggin@cyberone.com.au>]

Anthony R. wrote:

>Hi,
>  
>
>
>I would like to tune my kernel not to use as much memory for cache
>as it currently does. I have 2GB RAM, but when I am running one program
>that accesses a lot of files on my disk (like rsync), that program uses
>most of the cache, and other programs wind up swapping out. I'd prefer to
>have just rsync run slower because less of its data is cached, rather
>than have
>all my other programs run more slowly. rsync is not allocating memory,
>but the kernel is caching it at the expense of other programs.
>
>With 2GB on a system, I should never page out, but I consistently do and I
>need to tune the kernel to avoid that. Cache usage is around 1.4 GB!
>I never had this problem with earlier kernels. I've read a lot of comments
>where so-called experts poo-poo this problem, but it is real and
>repeatable and I am
>ready to take matters into my own hands to fix it. I am told the cache
>is replaced when
>another program needs more memory, so it shouldn't swap, but that is not
>the
>behaviour I am seeing.
>
>Can anyone help point me in the right direction?
>Do any kernel developers care about this?
>
>My kernel is stock 2.4.21, I run Redhat 9 on a 3GHz P4. I'd give you MB
>info but I've seen
>this behaviour on other motherboards as well.
>
>Thank you very much for your help.
>
>-- tony
>"Surrender to the Void." 
>-- John Lennon
>
>

Hi Anthony,
If you're up for a bit of work, give the "aa" series kernels a try, also
see how 2.6-test goes and be sure to report any problems you encounter.

The VM in stock 2.4 is slow to pick up updates due to being a stable series.
The problems definitely won't get poo-pooed here. Be sure you include a
good description of your workload and probably a log of vmstat 1 to start
with.