Date: Tue, 25 Jun 2002 17:23:18 -0700 From: Peter Wemm <peter@wemm.org> To: Terry Lambert <tlambert2@mindspring.com> Cc: Alfred Perlstein <bright@mu.org>, Patrick Thomas <root@utility.clubscholarship.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: tunings for many httpds... Message-ID: <20020626002318.C655D3811@overcee.wemm.org> In-Reply-To: <3D18CDB2.151978F3@mindspring.com>
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Terry Lambert wrote: > If you look at the commit message on version 1.48, you'll see that > without this option specified by the user, it eats KVA space, since > it eats KVM. The OBJT_PHYS was added specifically to support not > eating KVA space (by Peter, for Oracle, according to the comment). Uhh, Terry, neither form of SHM uses KVA. Either pageable or physically backed. The memory is only mapped into processes and is NOT mapped into KVA anywhere. (*) The difference between the normal and phys version is that the phys version uses raw pages and is not pageable. Since it is not pageable, we do not need PV entries (which are used to remove mappings in other address spaces when we are forcibly paging out a page). There are no other differences. The page table pages are still not shared (and live in process address space, not KVA) between multiple users of the SHM segment. Sharing large SHM's many ways consumes physical memory for page table pages. Non-phys-backed massively-shared SHM's also consume PV entries (28 bytes each), for which we set a fixed limit set at boot time. [* - fragments get mapped during page IO in the swap backed case.] Cheers, -Peter -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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