Re: [PATCH 1/2] fs: add a DCACHE_NEED_LOOKUP flag for d_flags

[Dave Chinner <david@fromorbit.com>]

On Sat, May 21, 2011 at 05:00:50AM +0200, Andi Kleen wrote:
> On Fri, May 20, 2011 at 08:30:19PM -0400, Josef Bacik wrote:
> > On 05/20/2011 05:31 PM, Andi Kleen wrote:
> > >> Putting them at the end of the cache LRU instead of the head would allow them to be dropped quickly under memory pressure. 
> > > 
> > > This still would fill up your memory for find /, potentially pushing
> > > out other stuff.
> > > 
> > > -Andi
> > 
> > So these things are just hashed on dput, so they don't have any
> > references to them and they are automatically put on the LRU list, so if
> > we get under memory pressure they will be easily discarded, especially
> > if nobody is actually stating them.  Thanks,
> 
> They are allocated. The allocation will push out other things too.
> There's no mechanism to only push dentries when allocating other dentries,
> or limit the total consumption from the dcache.

FWIW, I'm in the process of resurrecting my per-superblock VFS cache
shrinker patch which would make doing such limiting easier.  That
is, the fake dentries could be accounted and tracked on their own
per-sb LRU and when over a threshold (global and/or per-sb) the
per-sb shrinker could be called directly to free a number of fake
dentries. That way the sb generating them all would self-limit
without greatly affecting the working set of dentries on other
filesystems...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com