util-linux-2.12e

[nestu]

Hello everyone,
I just thought you may just find this interesting (sorry, a 
little long). This came to me as a fwd from a LFS list.

<paste>
-------- Original Message --------
Subject: OOM & [OT] util-linux-2.12e
Date: Mon, 20 Sep 2004 00:05:02 +0200 (MEST)
From: <Andries.Brouwer at cwi.nl>
To: linux-kernel at vger.kernel.org

Just released (on ftp.win.tue.nl in 
/pub/linux-local/utils/util-linux)
util-linux-2.12e.

The reason for this release were complaints that mount and 
umount
OOM the kernel when the number of mounts is large.
And indeed - I tried with 30000 mounts and the OOM-killer killed
everything in sight, including X's console, making X exit, 
killing
all remaining processes.

The new versions have been polished a little bit so as not 
to waste
too much memory, and now survive the 30000 mount/umount test 
for me.
Further polishing is needed for the case of large numbers of 
mounts;
when /etc/mtab is not a symlink to /proc/mounts then umount 
-a has
quadratic behaviour (it updates mtab after each unmount) and 
that
gets terribly slow.

About OOM: I am still of the opinion that the default state 
of the
kernel must be one where OOM does not occur and malloc() 
tells us
that we are out of memory. A system that suddenly decides to 
kill
all processes is really very poor and unreliable.
Users can enable other behaviours if they don't care about 
reliability.

About mount: I wondered whether I should rewrite [u]mounts's 
handling
of /etc/mtab so as to be a bit faster. But it seems a waste 
of time -
/proc/mounts has many advantages: automatically up-to-date, 
correct
also when namespaces are used, much faster. On the other 
hand, /etc/mtab
contains mount options that are sometimes needed later.
If it were possible to store the mount options in the 
kernel, making
them visible in /proc/mounts, then we could forget /etc/mtab 
altogether.

People have asked repeatedly for a way to mark lines in 
/etc/fstab
so as to make clear that such lines are managed by some GUI 
or other
external program. Labels like "kudzu".
In this release I added a comment convention for /etc/fstab: 
options
can have a part starting with \; - that part is ignored by mount
but can be used by other programs managing fstab.

If we would put the mount options in /proc/mounts, and 
introduced
a comment convention (say, the part starting with \: is 
ignored by
the kernel but can be used by programs reading /proc/mounts),
then /etc/mtab can die. Comments? Better solutions?

About util-linux and stuff: I have maintained various packages
for ten years or so - it may be time to pass things on to 
someone else.
Write to aeb at cwi.nl if you are interested in taking over or
co-maintaining kbd or man or man-pages or util-linux.

Andries
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</paste>

Ciao,
nestu ;)
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