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

[Al Viro]

On Fri, Jul 06, 2018 at 03:32:45PM -0400, Waiman Long wrote:

> With a 4.18 based kernel, the positive & negative dentries lookup rates
> (lookups per second) after initial boot on a 2-socket 24-core 48-thread
> 64GB memory system with and without the patch were as follows: `
> 
>   Metric                    w/o patch  neg_dentry_pc=0  neg_dentry_pc=1
>   ------                    ---------  ---------------  ---------------
>   Positive dentry lookup      584299       586749	   582670
>   Negative dentry lookup     1422204      1439994	  1438440
>   Negative dentry creation    643535       652194	   641841
> 
> For the lookup rate, there isn't any signifcant difference with or
> without the patch or with a zero or non-zero value of neg_dentry_pc.

Sigh...  What I *still* don't see (after all the iterations of the patchset)
is any performance data on workloads that would be likely to feel the impact.
Anything that seriously hits INCLUDE_PATH, for starters...