[CentOS] kbcached tuning on CentOS 4
Daniel de Kok
danieldk at pobox.com
Tue Sep 12 21:59:40 UTC 2006
On Mon, 2006-09-11 at 11:30 -0400, Justin Randall wrote:
> The real concern comes from administrators or other less technical staff
> logging into the box, and getting concerned at the amount of memory used
> up. Although user education is always positively accepted, the general
> comfort level would be much higher if they could login to a host and not
> see that 98% of memory is in use.
Now, that would be a bad reason for tinkering with VM
parameters, /etc/motd solves this problem ;).
> Regarding performance, this isn't much of a concern, although this host
> is intermittently hit with large work loads (which is why the kernel
> cache reaches the point of consuming all memory) which consume much
> memory, and another thought was that when these sporadic work loads
> proceed, there would be a slight performance hit waiting for free memory
> to be available as the cache is cleared.
Usually there is no such thing as literally clearing a cache. E.g. for
the page cache the kernel keeps a list for active pages, and one for
inactive pages. So, claiming pages is just a matter of dequeuing pages
from the inactive list. Or if the inactive list becomes to short, moving
pages from the active list to the inactive list if they weren't
Queuing/dequeuing of items to/from a list are mostly pointer operations,
which are very fast, and nowhere as expensive as a cache miss. As I said
in my previous e-mail, you need real good reasons to want to change the
default kernel VM behavior. Of course, it's your system :).
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