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

[Peter Zaitsev]

On Wed, 2004-07-14 at 15:44, Andrew Morton 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 ? 
> 
> If the kernel has no swap there is nothing it can do with an anonymous page
> (ie: the thing whcih malloc() gives you).  It is effectively pinned memory,
> because there's nowhere we can write it to get rid of it.

Why can't it be moved to other zone if there is a lot of place where ?
In general I was not pushing system in some kind of stress mode - There
was still a lot of cache memory available. Why it could not be instead
shrunk to accommodate allocation ? 

As I understand in my case with 4G there is  Normal zone and HighMem
zone where "user" anonymous memory can be located in any of these zones.
Is this observation correct ? 

 
> 
> If you end up pinning all of your ZONE_NORMAL pages with anonymous memory,
> further GFP_KERNEL allocation attempts will go oom.

Aha I see. So user level memory allocations can't cause OOM only kernel
level allocations can ?   In this case why do not you have some reserved
amount of space for these types of allocations by default ? 

In this case I also do not understand how swap space helps here ? If you
can't move page to over zone or shrink cache because of allocation type
how it happens you can however perform page swap ? 



-- 
Peter Zaitsev, Senior Support Engineer
MySQL AB, www.mysql.com



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