Date: Fri, 23 Mar 2001 19:29:39 +0100 (MET)
From: Andries.Brouwer@cwi.nl
Message-Id: <UTC200103231829.TAA06442.aeb@vlet.cwi.nl>
To: alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Prevent OOM from killing init
Sender: linux-kernel-owner@vger.kernel.org

On Fri, Mar 23, 2001 at 05:04:07PM +0000, Alan Cox wrote:
> > This is just an escape route in case everything else has failed.
> >
> > Linux is unreliable.
> > That is bad.
>
> Since your definition of reliability is a mathematical abstraction requiring
> infinite storage why don't you start by inventing infinitely large SDRAM
> chips, then get back to us ?

Ah, Alan,
I can see that you dislike seeing me say bad things about Linux.
I dislike having to say them.

On the other hand, my definition of reliability does not require
infinite storage. After all, earlier Unix flavours did not need
an OOM killer either, and my editor was not killed under Unix V6
on 64k when I started some other process.

Linux is unreliable because a program can be killed at random,
without warning, because of bugs in some other program.
The old Unix guarantee that a program only crashes because of
its own behaviour is lost. That is very sad.

What can one do? I need not tell you - you know better than I do.
The main point is letting malloc fail when the memory cannot be
guaranteed. There are various solutions for stack space, none of
them very elegant, but all have in common that when we run out of
stack space the program doing that gets SIGSEGV, and not some
random other program. (And a well-written program could catch this
SIGSEGV and do cleanup, preserving the integrity of its data base.
Clearly one would want to guarantee a certain minimum stack space
at fork time.)

Will this setup be very inefficient? I don't know. Perhaps.
If my programs actually use 10 MB but have a guarantee for
200 MB then the rest of that memory is not wasted. But it can
only be used for things that can be freed when needed, like
inode and buffer cache.

But inefficient or not, I much prefer a system with guarantees,
something that is reliable by default, above something that
works well if you are lucky and fails at unpredictable moments.

Andries
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