Date: Wed, 29 Mar 2000 23:31:48 -0800 From: Peter Wemm <peter@netplex.com.au> To: "Daniel O'Connor" <doconnor@gsoft.com.au> Cc: cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/alpha/include vmparam.h src/sys/conf opt Message-ID: <20000330073148.4E7BA1CD7@overcee.netplex.com.au> In-Reply-To: Message from "Daniel O'Connor" <doconnor@gsoft.com.au> of "Thu, 30 Mar 2000 16:49:57 %2B0930." <XFMail.000330164957.doconnor@gsoft.com.au>
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"Daniel O'Connor" wrote: > > On 30-Mar-00 Peter Wemm wrote: > > that comment is bogus.. The only practical limit is how much physical > > ram you want to lock up as this stuff isn't paged out or swap backed. > > Is it [easily] possible to make its pageable? I don't know. Probably, if one wanted to cut/paste code from the likes of the swap-backed code in the vn device. However, the other reason I'm not sure about making it pageable is that in a certain scenario making it pageable rules out a possible optimization. For example, an Oracle server, with a 1G shm segment (262144 pages) mapped into 300 processes consumes about 78643200 pv entries. At 28 bytes each that is 2202009600 bytes of ram (2100MB), *just for the pv entries*. Naturally this sucks as the pv entries are thrashed to hell. One of the main reasons for pv entries existing is to locate all virtual addresses in all processes that a given page occupies in order to rapidly unwire it during pageout. If the pages are never paged out and are permanently wired, then perhaps we could cheat somewhere and *not use* pv entries for these shm pages. This would make an astronomical difference to our Oracle TPS performance. Of course, it may not be possible to do this for other reasons, but making it pageable would guarantee it for now without rearchitecting the whole pv entry system (which is outside the scope of a quick hack to make oracle work better). Cheers, -Peter To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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