linux-kernel - Re: Hardcore trashing without any swap

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Message-Id: <201006110947.24286.edt@aei.ca>
Date:	Fri, 11 Jun 2010 09:47:23 -0400
From:	Ed Tomlinson <edt@....ca>
To:	László Monda <laci@...da.hu>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"linux-kernel" <linux-kernel@...r.kernel.org>
Subject: Re: Hardcore trashing without any swap

On Friday 11 June 2010 08:53:50 László Monda wrote:
> On Fri, Jun 11, 2010 at 2:16 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> > On Fri, 11 Jun 2010 02:10:33 +0200
> > László Monda <laci@...da.hu> wrote:
> >
> >> Hi List,
> >>
> >> The problem I'm facing with is very simple, yet extremely irritating
> >> in nature.  I have a laptop with 4G RAM and I don't use any swap.
> >> Whenever the RAM is full my system keeps trashing.  This makes X and
> >> SSH completely unresponsive for about a hour then a bunch of processes
> >> gets killed and it's usable again.
> >>
> >> How is possible that my system is trashing even though I don't use any swap?
> >
> > Because you don't have any swap. Its having to dump stuff it doesn't want
> > to like bits of applications that it can retrieve back from disk.
> 
> I can read what you wrote but cannot really understand it.  Please
> tell me where my logic fails:
> 
> No swap -> no dedicated space on disk to dump stuff -> no disk I/O
> should happen at all

No.  This is not the case.  If the vm needs memory it will discard pages from that are
backed by objects _not_ stored in swap - like executables.  Only if there is nothing to
discard will it start killing...  That being said you need to read up on what Alan's 
suggestion below does - or add a swapfile (which works nearly as well as a swap partition 
now).

> >> I'd expect the kernel to immediately kill the largest process without
> >> any trashing so I could continue my work right after the event.  How
> >> is it possible to configure?

See above.  Its not out of memory that it can discard without killing... 

> > It isn't.
> >
> > However if you want to avoid overcommit and thrashing play with
> >
> > /proc/sys/vm/overcommit*

Ed
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