Re: dentry cache leak? Re: rsync out of memory 2.6.8-rc2

Nick Piggin
2004-07-29T03:31:46Z

Klaus Dittrich wrote:

> Nick Piggin wrote:
>
>>
>> Your vfs_cache_pressure probably wants to be higher than 500. Make it
>> 10000.
>
>
> *No problems when using 10000.
> But I think of this as workaround only.
>

Yes it is just a workaround.

> I have read the "Scaling dcache with RCU" article from linuxjournal.com
> to get some insight how things should work. Pretty complicated.
>

Yes, prune_dcache is the only one called in response to memory pressure.
Basically you wouldn't have to worry about dcache internals for your sort
of machine. For example, RCU delayed freeing would not cause any problem.

The problem has probably been triggered either by a small change in the
page scanner, however the underlying problem is that the slab pressure
calculation isn't ideal on highmem systems, so in vfs intensive workloads
(lots of files), it is easy for ZONE_NORMAL allocations to OOM without
actually scanning much slab.