• Alexey Dobriyan's avatar
    mm: unrig VMA cache hit ratio · 131ddc5c
    Alexey Dobriyan authored
    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: default avatarAlexey Dobriyan <adobriyan@gmail.com>
    Cc: Davidlohr Bueso <dave@stgolabs.net>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    131ddc5c
vmacache.c 3.13 KB