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Date: Fri, 6 Jul 2018 23:28:14 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Waiman Long <longman@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-doc@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jan Kara <jack@suse.cz>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	Miklos Szeredi <mszeredi@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	Larry Woodman <lwoodman@redhat.com>,
	James Bottomley <James.Bottomley@HansenPartnership.com>,
	"Wangkai (Kevin C)" <wangkai86@huawei.com>
Subject: Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries
Message-ID: <20180706222814.GE30522@ZenIV.linux.org.uk>
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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...