On Sun, Sep 11, 2005 at 11:16:36PM -0400, Theodore Ts'o wrote:
> On Sun, Sep 11, 2005 at 05:30:46PM +0530, Dipankar Sarma wrote:
> > Do you have the /proc/sys/fs/dentry-state output when such lowmem
> > shortage happens ?
> 
> Not yet, but the situation occurs on my laptop about 2 or 3 times
> (when I'm not travelling and so it doesn't get rebooted).  So
> reproducing it isn't utterly trivial, but it's does happen often
> enough that it should be possible to get the necessary data.
> 
> > This is a problem that Bharata has been investigating at the moment.
> > But he hasn't seen anything that can't be cured by a small memory
> > pressure - IOW, dentries do get freed under memory pressure. So
> > your case might be very useful. Bharata is maintaing an instrumentation
> > patch to collect more information and an alternative dentry aging patch 
> > (using rbtree). Perhaps you could try with those.
> 
> Send it to me, and I'd be happy to try either the instrumentation
> patch or the dentry aging patch.
> 

Ted,

I am sending two patches here.

First is dentry_stats patch which collects some dcache statistics
and puts it into /proc/meminfo. This patch provides information 
about how dentries are distributed in dcache slab pages, how many
free and in use dentries are present in dentry_unused lru list and
how prune_dcache() performs with respect to freeing the requested
number of dentries.

Second is Sonny Rao's rbtree dentry reclaim patch which is an attempt
to improve this dcache fragmentation problem.

These patches apply on 2.6.13-rc7 and 2.6.13 cleanly.

Could you please apply the dcache_stats patch and check if the problem
can be reproduced. When that happens, could you please capture the 
/proc/meminfo, /proc/sys/fs/dentry-state and /proc/slabinfo.

It would be nice if you could also try the rbtree patch to check if
it improves the situation. rbtree patch applies on top of the stats
patch.

Regards,
Bharata.