Re: oom kill oddness.

[Dave Jones <davej@redhat.com>]

On Thu, Sep 28, 2006 at 05:17:06PM -0700, Andrew Morton wrote:
 > On Fri, 29 Sep 2006 01:03:16 +0200 (CEST)
 > Roman Zippel <zippel@linux-m68k.org> wrote:
 > 
 > > Hi,
 > > 
 > > On Wed, 27 Sep 2006, Dave Jones wrote:
 > > 
 > > > So I have two boxes that are very similar.
 > > > Both have 2GB of RAM & 1GB of swap space.
 > > > One has a 2.8GHz CPU, the other a 2.93GHz CPU, both dualcore.
 > > > 
 > > > The slower box survives a 'make -j bzImage' of a 2.6.18 kernel tree
 > > > without incident. (Although it takes ~4 minutes longer than a -j2)
 > > > 
 > > > The faster box goes absolutely nuts, oomkilling everything in sight,
 > > > until eventually after about 10 minutes, the box locks up dead,
 > > > and won't even respond to pings.
 > > > 
 > > > Oh, the only other difference - the slower box has 1 disk, whereas the
 > > > faster box has two in RAID0.   I'm not surprised that stuff is getting
 > > > oom-killed given the pathological scenario, but the fact that the
 > > > box never recovered at all is a little odd.  Does md lack some means
 > > > of dealing with low memory scenarios ?
 > > 
 > > I think I see the same thing on the other end on slow machines, here it 
 > > only takes a single compile job, which doesn't quite fit into memory and 
 > > another task (like top) which occasionally wakes up and tries to allocate 
 > > memory and then kills the compile job - that's very annoying.
 > > 
 > > AFAICT the basic problem is that "did_some_progress" in __alloc_pages() is 
 > > rather local information, other processes can still make progress and keep 
 > > this process from making progress, which gets grumpy and starts killing. 
 > > What's happing here is that most memory is either mapped or in the swap 
 > > cache, so we have a race between processes trying to free memory from the 
 > > cache and processes mapping memory back into their address space.
 > 
 > Kernel versions please, guys.  There have been a lot of oom-killer changes
 > post-2.6.18.

Sorry, I've been stuck on 2.6.18 as that's what we're shipping in FC6 soon.

	Dave
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