Re: [PATCH] vm: enhance __alloc_pages to prioritize pagecache eviction when pressed for memory

[Neil Horman <nhorman@tuxdriver.com>]

On Mon, Dec 12, 2005 at 12:16:39PM -0800, Andrew Morton wrote:
> Neil Horman <nhorman@tuxdriver.com> wrote:
> >
> > On Fri, Dec 09, 2005 at 04:29:01PM -0800, Andrew Morton wrote:
> > > Neil Horman <nhorman@tuxdriver.com> wrote:
> > > >
> > > > Hey all-
> > > >      I was recently shown this issue, wherein, if the kernel was kept full of
> > > > pagecache via applications that were constantly writing large amounts of data to
> > > > disk, the box could find itself in a position where the vm, in __alloc_pages
> > > > would invoke the oom killer repetatively within try_to_free_pages, until such
> > > > time as the box had no candidate processes left to kill, at which point it would
> > > > panic.
> > > 
> > > That's pretty bad.  Are you able to provide a description which would permit
> > > others to reproduce this?
> > 
> > As promised, heres the reproducer that was given to me, and used to reproduce
> > this problem:
> > 
> > 1) setup an nfs serve with a thread count of 2.  Of course, 1 thread might make
> > the problem more easy to reproduce.  I haven't tried it yet.
> > 
> > 2) Setup 4 nodes to hammer the nfs mounted directory.  The 4 nodes should hammer
> > out 4 gigs.  2 gigs didn't seem to be enough.
> > 
> > I used a locally developed tool called ior to reproduce this problem.  The tool
> > can be found here:
> > 
> > http://www.llnl.gov/asci/platforms/purple/rfp/benchmarks/limited/ior/
> > 
> > I suppose anything that can write to NFS fast should be fine.  But that's what I
> > did.
> > 
> > 
> > If you do this, any node writing to the server that has more than 4GB of RAM
> > should start oom killing to the point where it runs out of candidate processes
> > and panics
> 
> We merged an NFS fix last week which will help throttling under heavy
> writeout conditions..
This one?
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=bb713d6d38f7be4f4e7d790cddb1b076e7da6699
I guess I must have just missed it during my testing. I'll give it a spin and
let you know if it fixes my test case.

Thanks & Regards
Neil

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 *Neil Horman
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