Re: [PATCH 3/5] superblock: introduce per-sb cache shrinker infrastructure

Dave Chinner
2010-05-27T04:05:11Z

On Thu, May 27, 2010 at 12:19:05PM +1000, Nick Piggin wrote:
> On Thu, May 27, 2010 at 09:12:14AM +1000, Dave Chinner wrote:
> > On Thu, May 27, 2010 at 02:41:16AM +1000, Nick Piggin wrote:
> > > > + count = ((sb->s_nr_dentry_unused + sb->s_nr_inodes_unused) / 100)
> > > > + * sysctl_vfs_cache_pressure;
> > >
> > > Do you think truncating in the divisions is at all a problem? It
> > > probably doesn't matter much I suppose.
> >
> > Same code as currently exists. IIRC, the reasoning is that if we've
> > got less that 100 objects to reclaim, then we're unlikely to be able
> > to free up any memory from the caches, anyway.
>
> Yeah, which is why I stop short of saying you should change it in
> this patch.
>
> But I think we should ensure things can get reclaimed eventually.
> 100 objects could be 100 slabs, which could be anything from
> half a meg to half a dozen. Multiplied by each of the caches.
> Could be significant in small systems.

True, but usually there are busy objects in the dentry and inode
slabs, so it shouldn't be a significant issue. We can probably
address such problems if they can be demonstrated to be an issue in
a separate patch set....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com