Re: fallout of 16K stacks

From: Linus Torvalds
Date: Mon Jul 07 2014 - 19:52:42 EST


On Mon, Jul 7, 2014 at 4:04 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
>>
>> As in ENOMEM or does something worse happen?
>
> EAGAIN, then the workload stops. For an overnight stress
> test that's pretty catastrophic. It may have killed some stuff
> with the OOM killer too.

I don't think it's OOM.

We have long had the rule that order <= PAGE_ALLOC_COSTLY_ORDER (which
is 3) allocations imply __GFP_RETRY unless you explicitly ask it not
to.

And THREAD_SIZE_ORDER is still smaller than that.

Sure, if the system makes no progress at all, it will still oom for
allocations like that, but that's *not* going to happen for something
like a 32GB machine afaik.

And if it was the actual dup_task_struct() that failed (due to
alloc_thread_info_node() now failing), it should have returned ENOMEM
anyway.

So EAGAIN is due to something else.

The only cases for fork() returning EAGAIN I can find are the
RLIMIT_NPROC and max_threads checks.

And the thing is, the default value for RLIMIT_NPROC is actually
initialized based on THREAD_SIZE (which doubled), so maybe it's really
just that rlimit check that now triggers.

Hmm?

Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/