Kai Schaetzl wrote:
Feizhou wrote on Tue, 06 Jun 2006 10:54:26 +0800:
Yeah but with that patch that changed the vm system behaviour, setting
swappiness to 0 had ZERO effect. The kernel happily swapped out what
data it could from programs that were running.
But you apparently need some additional environmental condition for this
to happen. I see normal behavior as ever with my 4.3. After boot it slowly
fills up memory until less than 50 MB is left. If the machine is scarce on
memory it even gets almost to zero physical mem left. swap file usage
stays at a few 100k. I don't have desktop machines, only servers. I
suspect that the problematic behavior occurs only when you close
applications. In that case it might swap the diskcache of the closed
application out instead of keeping it in RAM. On a server this doesn't
happen, you have your applications running continuously and no big memory
eaters that don't run all the time - well there are exceptions, of course.
I don't suppose you are running on AMD64? The patch only affects Intel
processor-based boxes.
Here chew this:
https://bugzilla.redhat.com/bugzilla/attachment.cgi?id=129064
My previous colleagues all think that RHEL4 or Centos 4 is slow which is
true but due to the dumb vm patch Redhat applied to the RHEL4 kernel
which is makes the box swap.
I do not access to those boxes now but I can tell you that vmstat will
report swapping activity with constant non-zero figures under si and so.
That is swapping. Hence, vmstat will also have high numbers under wa and
id due to the apps all waiting for i/o on the RHEL4 box. The FC4 has
completely different vmstat reports which are basically zero swapping,
full utilization (cpu idle = 0) and zero or low wa numbers.
Redhat has admitted as much that the problem was their vm patch. Setting
swappiness or whatever has zero bearing on the current RHEL4 kernel's
knack of writing pages to swap even though there is plenty of RAM available.
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