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

Andrew Morton
2004-07-30T19:49:42Z

Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
>
> On Thu, Jul 29, 2004 at 02:07:43PM -0700, Andrew Morton wrote:
> > kladit@t-online.de (Klaus Dittrich) wrote:
> > >
> > > >Can you narrow the onset of the problem down to any particular kernel
> > > >snapshot?
> > >
> > > Did it and here is the answer.
> > >
> > > kernel-2.6.7 and bk's up to 2.6.7-bk7 survived a du -s,
> > > kernels starting with 2.6.7-bk8 did not.
> >
> > I can reproduce this oom btw. Am (very, very slowly) working out what's
> > causing it. It's unrelated to the vfs-cache-pressure patch. I'd hope to
> > have it fixed up for 2.6.8.
>
> Odd, because the only thing I can see which affects dcache related code
> between -bk7 and -bk8 is the vfs-cache-pressure patch.

It can be triggered with that patch reverted.

> What are the exact steps you're using to reproduce the leak?

Just a `du -s' over zillions of files on a 2G machine.

> And where do you think the problem lies?

Seems that we reach a state where lowmem pagecache get reclaimed faster
than dcache/icache. This causes the number of pages scanned for lowmem
allocations to fall. This causes less scanning of the slab and the whole
thing repeats. I expect changing nr_used_zone_pages() to ignore highmem
will fix it, and might be the long-term fix, too.