On Mon, Jul 16, 2018 at 11:09:01AM +0200, Michal Hocko wrote:

On Fri 13-07-18 10:36:14, Dave Chinner wrote:
[...]

quoted

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.
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