Current code doesn't count first FIND operation after VMA cache flush
(which happen surprisingly often) artificially increasing cache hit ratio.

On my regular setup the difference is:

		Before				After
	==========================================================

	* boot, login into KDE

	vmacache_find_calls 446216	vmacache_find_calls 492741
	vmacache_find_hits 277596	vmacache_find_hits 276096

		~62.2%				~56.0%

	* rebuild kernel (no changes to code, usual config)

	vmacache_find_calls 1943007	vmacache_find_calls 2083718
	vmacache_find_hits 1246123	vmacache_find_hits 1244146

		~64.1%				~59.7%

	* rebuild kernel (full rebuild, usual config)

	vmacache_find_calls 32163155	vmacache_find_calls 33677183
	vmacache_find_hits 27889956	vmacache_find_hits 27877591

		~88.2%				~84.3%

Total: ~4% cache hit ratio.

If someone is counting _relative_ cache _miss_ ratio, misreporting is much
higher.

Link: http://lkml.kernel.org/r/20160822225009.GA3934@p183.telecom.bySigned-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>