linux-kernel - Re: OOM killer gripe (was Re: What still uses the block layer?)

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Message-Id: <200710150452.30939.rob@landley.net>
Date:	Mon, 15 Oct 2007 04:52:30 -0500
From:	Rob Landley <rob@...dley.net>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Theodore Tso <tytso@....edu>,
	James Bottomley <James.Bottomley@...eleye.com>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Nick Piggin <piggin@...erone.com.au>
Subject: Re: OOM killer gripe (was Re: What still uses the block layer?)

On Monday 15 October 2007 8:37:44 am Nick Piggin wrote:
> > Virtual memory isn't perfect.  I've _always_ been able to come up with
> > examples where it just doesn't work for me.  This doesn't mean VM
> > overcommit should be abolished, because it's useful more often than not.
>
> I hate to go completely offtopic here, but disks are so incredibly
> slow when compared to RAM that there is really nothing the kernel
> can do about this.

I know.

> Presumably the job will finish, given infinite 
> time.

I gave it about half an hour, then it locked solid and stopped writing to the 
disk at all.  (I gave it another 5 minutes at that point, then held down the 
power button.)

Lost about 50 open konqueror tabs...

> How much swap do you have configured?

2 gigs, same as ram.

> You really shouldn't configure 
> so much unless you do want the kernel to actually use it all, right?

Two words: "Software suspend".  I've actually been thinking of increasing it 
on the next install...

> Because if we're not really conservative about OOM killing, then the
> user who actually really did want to use all the swap they configured
> gets angry when we kill their jobs without using it all.

I tend to lower "swappiness" and when that happens all sorts of stuff goes 
weird.  Software suspend used to say says it can't free enough memory if I 
put swappiness at 0 (dunno if it still does).  This time the OOM killer never 
triggered before hard deadlock.  (I think I had it around 20 or 40 or some 
such.)

> Would an oom-kill-someone-now sysrq be of help, I wonder?

*shrug* It might.  I was a letting it run hoping it would complete itself when 
it locked solid.  (The keyboard LEDs weren't flashing, so I don't _think_ it 
paniced.  I was in X so I wouldn't have seen a message...)

(To be honest, I can never remember how to trigger sysrq on a laptop keyboard.  
Presumably X won't intercept it the way it does alt-f1 and ctrl-alt-del...)

Rob
-- 
"One of my most productive days was throwing away 1000 lines of code."
  - Ken Thompson.
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