Date: Wed, 05 Jan 2011 12:51:44 +0100 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-performance@freebsd.org Subject: Re: tunning disk cache for pgsql? Message-ID: <ig1m0g$7k9$1@dough.gmane.org> In-Reply-To: <20101231090612.GN2660@baneblade.noc.nerim.net> References: <20101228135940.GE2660@baneblade.noc.nerim.net> <AABD98FE-DA25-4A09-86D6-EBC341040A35@nasby.net> <20101231090612.GN2660@baneblade.noc.nerim.net>
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On 31/12/2010 10:06, Nicolas Haller wrote: > Someone knows if there is a page which explains FreeBSD mechanisms about > memory and fs cache management? I think I must read something on it :-) I don't think there's a single up to date document describing all of it, but it's conceptually simple and similar to what other OSes do. It's just that "top" output is somewhat verbose and low-level. You can start here: http://www.freebsd.org/doc/en/books/arch-handbook/vm.html (it's a bit outdated). Basically, to support both mmap() and read() / write(), the OS thinks of everything in terms of memory pages. When an application reads or writes something from / to a file, it's a "page-in" or "page-out" of a sort, and the page gets put in the active list. After some time it spends unused by the process, it's moved to the inactive list, then to the cache list. These separate lists exist AFAIK mostly to speed up searching.
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