Date: Thu, 30 Nov 1995 00:10:31 +0000 () From: "John S. Dyson" <toor@dyson.iquest.net> To: terry@lambert.org (Terry Lambert) Cc: taob@io.org, freebsd-hackers@FreeBSD.ORG Subject: Re: Increasing size of shared memory segmenty Message-ID: <199511300010.AAA04609@dyson.iquest.net> In-Reply-To: <199511292110.OAA28629@phaeton.artisoft.com> from "Terry Lambert" at Nov 29, 95 02:10:47 pm
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> > In the course of playing with the gimp image editor (see the > > freebsd-ports list if you don't know what this is), I keep bumping > > into the 4-megabyte shared memory segment limit. What is the best way > > to increase this size? Define SHMMAX in the kernel config file? Or > > SHMALL or SHMMAXPGS? The gimp documentation suggests a 32-megabyte > > segment size. > > You can bump the max pages in a segment. Be aware that the kernel > address space is limited, and is further restricted above and beyond > what you'd expect by the vm/buffer cache unification. There is not > a mechanism for windowed access to large files. > On FreeBSD, not all of the cached pages (both VFS created, and VM created) are mapped into the kernel. This keeps the size of the kvm down. However you are essentially correct given the question -- the Sys5 shared memory scheme has a major limitation that it actually maps the pages into the kernel?!!?@!?@ That is kind of nonsense, but that was the implementation. I have started off/on to rewrite it "sysv_shm" to work properly, but other things have been more pressing. > > 32M is smaller than the overall limit, (36 bits? 39 bits?) so you should > be safe, though if you have several of these, you will probably start > having problems. > The limit today is 31 Bits :-(. But the code that I am running today is 39 Bits with perhaps 40 Bits in the offing. It is unlikely that we will need to use more than a 31 Bit window on a Pentium :-), but now at least we will be able to have at least 1Tb files with the merged VM buffer cache scheme. John dyson@freebsd.org
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