Horton

Re: MMAP Buffers

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: pgsql-hackers@postgresql.org
Cc: Radosław Smogura <rsmogura@softperience.eu>, Tom Lane <tgl@sss.pgh.pa.us>, Peter Eisentraut <peter_e@gmx.net>, Greg Stark <gsstark@mit.edu>, Robert Haas <robertmhaas@gmail.com>, Greg Smith <greg@2ndquadrant.com>, Joshua Berkus <josh@agliodbs.com>, Andrew Dunstan <andrew@dunslane.net>, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Date: 2011-04-17T18:02:11Z
Lists: pgsql-hackers 
On Sunday 17 April 2011 19:26:31 Radosław Smogura wrote:
> Kernel merges vm_structs. So mappings are compacted. I'm not kernel 
> specialist, but skipping memory consumption, for not compacted mappings, 
> kernel uses btrees for dealing with  TLB, so it should not matter if there
> is  100 vm_structs or 100000 vm_structs.
But the CPUs TLB cache has maybe 16/256 (1lvl, 2nd) to 64/512 entries. That 
will mean that there will be cachemisses all over.
Additionally your scheme requires flushing it regularly...

Andres