Re: OOM kills if swappiness set to 0, swap storms otherwise

[Linda Walsh <lkml@tlinx.org>]

Charles Shannon Hendrix wrote:
> Mon, 27 Mar 2006 @ 19:59 -0800, Andrew Morton said:
>
>   
> > Much porkiness.
> >
> > /proc/meminfo is very useful for obtaining a top-level view of where all
> > the memory's gone to.  I'd tentatively say that your options are to put up
> > with the swapping or find a new mail client.
> >     
>
> I use mutt for my email, and I have the same issue on a 1GB system.
>
> I really wish we could put an upper limit on what file cache can use.
>   
----
   Hmmm, not to be contrary, but I have a 1GB system that refuses to swap
during large file i/o operations.  For the first time in a *long* time,
I read someone's suggestion to increase swappiness -- I did, to 75 or 80,
(I've booted since then, so it's back to 60 and no swap usage) and some of
the programs that rarely run actually swapped.  It was great!  I finally had
more memory for file i/o operations.

   Maybe you are telling the system to "feel free" to use swap by having a
large swap file?  I have a 256Mb swap partition near the front of the disk
where I/O is fastest, but it usually remains untouched, but that also means
I can only overcommit used memory by 25% (1Gphys, 256M swap).  I don't know
what the OOM "looks like" when it runs.  I had a buggy perlapp, once, that
tried to consume infinite memory, but I think it segfaulted before the OOM
could act.

   Maybe if you don't want linux to swap as much, it might swap less if 
you give
it less to swap with?  I know it sounds simplistic, but I've run with 
smallish
swap files ever since I got up to 1GB of main memory.  The only reason I 
have one
at all is I presumed that infrequently used functions, like dhcp (only 
used when
friends are over) would be shuffled out -- but it isn't unless I increase
swappiness.
> I shouldn't be suffering from swap storms.
>   
I agree.  Try getting rid of your swap file entirely -- your system will 
still
run unless you are overloading memory, but you have a Gig.  How much do you
need to keep in memory?  Sure, if/when I get a 4-way CPU (I have a 2-cpu 
setup now),
I might go up to 4G, but I might be running multiple virtual machines too!
> For example, my normal working set of programs eats about 250MB of memory. If
> I also start a job running to something like tag some mp3s, copy a CD, or just
> process a lot of files, it only takes a few minutes before performance becomes
> unacceptable.  
>   
---
   You might try the "cfq" block i/o algorithm.  Then you can
ionice down the disk priority of background processes (though you need
to be root to reduce ionice levels at this point, unlike cpu nice).
> If you are doing some work where you switch among several applications
> frequently, the pigginess of file cache becomes a serious problem.
>   
---
   Never a problem.  I don't allocate enough swap for it to be a 
problem I'm
guessing. Programs stay in memory and blocks get forced out to disk more
frequently.

Linda
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