Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries

[Matthew Wilcox]

On Mon, Jul 16, 2018 at 11:09:01AM +0200, Michal Hocko wrote:
> On Fri 13-07-18 10:36:14, Dave Chinner wrote:
> [...]
> > By limiting the number of negative dentries in this case, internal
> > slab fragmentation is reduced such that reclaim cost never gets out
> > of control. While it appears to "fix" the symptoms, it doesn't
> > address the underlying problem. It is a partial solution at best but
> > at worst it's another opaque knob that nobody knows how or when to
> > tune.
> 
> Would it help to put all the negative dentries into its own slab cache?

Maybe the dcache should be more sensitive to its own needs.  In __d_alloc,
it could check whether there are a high proportion of negative dentries
and start recycling some existing negative dentries.