Re: VM Problems in 2.6.7 (Too active OOM Killer)

[William Lee Irwin III]

On Wed, Jul 14, 2004 at 07:39:51PM -0700, William Lee Irwin III wrote:
>> Careful not to make too much of ignoring signals, mm/oom_kill.c sets
>> PF_MEMDIE out-of-context, so when an OOM kill is issued while a task
>> is looping in __alloc_pages() it will eventually break out of the
>> rebalance loop due to the flag.

On Wed, Jul 14, 2004 at 07:44:47PM -0700, William Lee Irwin III wrote:
> However, note the modifications of task->flags are not atomic. In
> principle, one may have:
> __alloc_pages()			__oom_kill_task()
> load current->flags		load current->flags
> |= PF_MEMALLOC in registers	|= PF_MEMALLOC|PF_MEMDIE in registers
> IRQ/delay/whatever		store current->flags
> store current->flags		...
> try_to_free_pages() etc.	force_sig() etc.
> ... and voila! PF_MEMDIE in ->flags has been lost.

I have a testcase that panics in mm/oom_kill.c (no processes left) on
several kinds of machines with weaker memory consistency, but does not
on x86-64. I suspect it is related to lack of task->flags atomicity.


-- wli
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