Rob van der Heij wrote:
2009/5/8 Tomasz Westrych <[email protected]>:
How to clear memory cache in Sles 9 ? In SLES10 you can do "echo 3 >
/proc/sys/vm/drop_caches".
In SLES9 I, don't see drop_caches.
We have z/VM 5.4 + SLES9 version 2.6.5-7.244-s390x.
Right. This is a more recent addition to Linux memory management, and
it's not available in the older kernels.
Be aware that it does not really help you in reducing your real memory
requirements when running on z/VM. The reason is that z/VM is not
aware that Linux has freed up those pages, and z/VM will still retain
the data. In some cases, doing this will actually *increase* your real
memory requirements. If you want to do such things, look at CMM-1
(which is in SLES9).
It's really just a diagnostics tool, for example to make sure that
your benchmark is no cheating with a lot of data already loaded in
cache. It may also be helpful to understand the base requirements of
an application.
And for those of the other side listening in: there is a bug in one of
the RHEL5 kernels that causes Linux in a loop when you use drop_caches
in a very large server.
Rob
Sounds like this bug:
https://bugzilla.redhat.com/show_bug.cgi?id=444961
Patch was committed to 2.6.25-mm1, so for anyone making heavy use of
drop_caches, make sure to update to RHEL 5.3 (or the kernel at least).
--
Brad Hinson <[email protected]>
Sr. Support Engineer Lead, System z
Red Hat, Inc.
(919) 754-4198
www.redhat.com/z
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