Date: Sun, 14 Apr 1996 16:55:34 -0700 From: David Greenman <davidg@Root.COM> To: dyson@FreeBSD.org Cc: andreas@knobel.gun.de (Andreas Klemm), joerg_wunsch@uriah.heep.sax.de, groudier@iplus.fr, hackers@FreeBSD.org, linux-kernel@vger.rutgers.edu Subject: Re: Unices are created equal, but ... Message-ID: <199604142355.QAA04357@Root.COM> In-Reply-To: Your message of "Sun, 14 Apr 1996 18:22:20 CDT." <199604142322.SAA00427@dyson.iquest.net>
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>> Whole Linux seems to be a memory file system ;-) They are caching >> like hell. Only benchmarks like bonnie on files of about 3xRAMSIZE >> address the fact that we want to bench the disk and not the RAM. >> Gerard compares chicken with eggs. This Byte Bench is really >> questionable. >> >The most evil things about aggressively write cache are the memory starvation >and sync issues. On FreeBSD we purposely decided to limit the amount of >dirty cached file data. It can become a real problem with big memory >systems!!! The AT&T GIS/NCR/Tandem boxes really acted badly when users >would tune the system to allow too much memory to be dirty filesystem >cache buffers. I could be convinced that 1/4 of memory for dirty buffers >is okay, and in some cases even more could be considered. But those cases >where a system could gain significantly from huge write caches are few >and far between. I guess if managed VERY WELL, a large (>1/2 mem) write cache >would be good -- I just haven't seen that yet. Worst case, that would be about 256MB of cached data to write out on wcarchive. :-) I think I prefer the current scheme. :-) -DG David Greenman Core-team/Principal Architect, The FreeBSD Project
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