Re: VM balancing issues on 2.6.13: dentry cache not getting shrunk enough

[Marcelo <marcelo.tosatti@cyclades.com>]

Bharata,

On Sun, Oct 02, 2005 at 10:02:29PM +0530, Bharata B Rao wrote:
> 
> Marcelo,
> 
> The attached patch is an attempt to break the "slabs_scanned" into
> meaningful pieces as you suggested.
> 
> But I coudn't do this cleanly because kmem_cache_t isn't defined
> in a .h file and I didn't want to touch too many files in the first
> attempt.
> 
> What I am doing here is making the "requested to free" and
> "actual freed" counters as part of struct shrinker. With this I can
> update these statistics seamlessly from shrink_slab().
> 
> I don't have this as per cpu counters because I wasn't sure if shrink_slab()
> would have many concurrent executions warranting a lockless percpu
> counters for these.

Per-CPU counters are interesting because they avoid the atomic
operation _and_ potential cacheline bouncing. Given the fact that less
commonly used counters in the reclaim path are already per-CPU,
I think that it might be worth to do it here too.

> I am displaying this information as part of /proc/slabinfo and I have
> verified that it atleast isn't breaking slabtop.
> 
> I thought about having this as part of /proc/vmstat and using
> mod_page_state infrastructure as u suggested, but having the
> "requested to free" and "actual freed" counters in struct page_state
> for only those caches which set the shrinker function didn't look
> good.

OK... You could change the atomic counters to per-CPU variables
in "struct shrinker".

> If you think that all this can be done in a better way, please
> let me know.