From owner-freebsd-hackers Tue Jun 25 23:15:26 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from utility.clubscholarship.com (utility.clubscholarship.com [198.78.70.175]) by hub.freebsd.org (Postfix) with ESMTP id 980E037B4D6 for ; Tue, 25 Jun 2002 23:11:00 -0700 (PDT) Received: from localhost (root@localhost) by utility.clubscholarship.com (8.11.6/8.11.6) with ESMTP id g5Q67UJ23296; Tue, 25 Jun 2002 23:07:30 -0700 (PDT) (envelope-from root@utility.clubscholarship.com) Date: Tue, 25 Jun 2002 23:07:30 -0700 (PDT) From: Patrick Thomas To: Peter Wemm Cc: Terry Lambert , Alfred Perlstein , Subject: Re: tunings for many httpds... In-Reply-To: <20020626023154.A70723910@overcee.wemm.org> Message-ID: <20020625230407.B68572-100000@utility.clubscholarship.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG > Incidently, looking at the PV entry angle for a moment. Suppose you > create a 1GB sysvshm (pageable) segment. That's 262144 pages. Mapping this > once means you consume 262144 PV entries. At 28 bytes each, that is > about 7.3MB of KVM. Now, fork this process 300 times. The numbers become > 78643200 PV entries taking up about 2.2GB of PV entries that would like to fit > in the 1G KVA space. We dont even nearly have a way to fit all this in. > > This is the killer reason for SHM_PHYS stuff. It avoids the PV load which > has to fit into a single confined space. The cost of the page table pages > sucks, but at least that is spread over the VM space of 300 processes. Ok, I'm confused now - so I understood you to originally say that SHM does not eat into KVA regardless of whether I set the kern.ipc.shm_use_phys to '1' or not. This leads me to conclude that setting that sysctl to 1 will probably not be the magic bullet to stop my system from inexplicably halting. (my system with greatly (4x) increased SHM/SEM/etc. settings) But now in this post ... are you saying that from the "PV entry angle" that KVA _is_ sometimes used for SHM, when we create a pageable segment ? Or are you just providing a thought experiment and pointing out that if it _were_ done this way then XYZ bad things would occur ? thanks, PT To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message