Date: Sat, 31 Aug 2002 17:04:05 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: "Marc G. Fournier" <scrappy@hub.org> Cc: Arnvid Karstad <arnvid@karstad.org>, <bmah@FreeBSD.ORG>, <freebsd-stable@FreeBSD.ORG> Subject: Re: Problems with FreeBSD - causing zalloc to return 0 ?! Message-ID: <200209010004.g81045O1010756@apollo.backplane.com> References: <20020831200929.C14642-100000@mail1.hub.org>
next in thread | previous in thread | raw e-mail | index | archive | help
:> the swap bitmap. You can also reduce the kernel reservation for
:> swap block data by setting the kern.maxswzone boot environment
:> variable. This is in bytes, e.g. in /boot/loader.conf
:>
:> kern.maxswzone="32m"
:
:What exactly does this one mean? Or do? Will set it, but am curious ...
When FreeBSD swaps something to swap space it has to record the
(object,blockno)->swapblockno translation in order to be able to
figure out how to swap the page back in when a fault is taken.
This information is recorded in the swap zone. Approximate memory
usage, including overhead, is around 6 bytes per page swapped out.
A 32M KVM reservation (KVM, not physical ram) will thus allow
around 5 million pages == 22 GB to be swapped out.
The actual reservation is based on the amount of physical memory on
the machine but I've been way too generous in the past and I am still
too generous. Until the commit I made today the KVM meta storage
limit for swap information was 70MB of KVM. In commits I made today I
reduced the limit to 32MB of KVM and cut the calculation of the actual
swap zone based on physical memory in half (again).
This parameter only matters on machines with large amounts of ram
(> 1GB or so) since machines with less memory will calculate a smaller
maximum as a matter of course.
In anycase, we still do not know whether your particular problem is
related to KVM exhaustion or not. Your kernel config does not seem
particularly problemsome. Those live GDB commands I mentioned
are the best way to find out (well, a core is the best way to find out
but the GDB commands will work if no core is available). Generally
speaking recent FreeBSD 4.x releases have been chewing up more KVM
due to new features and a general push to properly balance resources
to give installations the most bang for the buck. It works very well
for nearly all installations but it will still break down if someone
makes huge changes in certain defaults and does not reduce other areas
of KVM use to make up the difference.
-Matt
Matthew Dillon
<dillon@backplane.com>
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-stable" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200209010004.g81045O1010756>