Re: VM Problems in 2.6.7 (Too active OOM Killer)

[Andrea Arcangeli]

On Wed, Jul 14, 2004 at 04:47:04PM -0700, Peter Zaitsev wrote:
> To be honest I do not really understand this OOM without swap problem at
> all, why is it possible to move pages from ZONE_NORMAL to swap but not
> to other zones ? 

the oom without swap you reproduced is not related to ZONE_NORMAL
shortage. The pages in ZONE_NORMAL never goes into swap.

the ZONE_NORMAL oom is a separate issue from the oom killing you
reproduced. with 2.6.7 if you were hitting the ZONE_NORMAL shortage your
machine would lockup and it would never oom-kill anything (Andrew just
changed that in kernel CVS, so thanks to that change a ZONE_NORMAL
shortage will not deadlock anymore in 2.6.8, but OTOH in 2.6.8 adding
swap will not be enough anymore to workaround the oom-killing you
reproduced).

About the ZONE_NORMAL shortage without swap, rather than running
cpu-cache-hungry memcopies from lowmemzone to highmem (or even worse to
pass through swap like it happens in 2.6 mainline with swap enabled), I
believe it's better to reserve some ram in the lowmem zone, 800M of ram
on a 32G box should be a cheap price to pay compared to the cpu/IO cost
involved in moving memory around during the bench.
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