linux-kernel - Re: fallout of 16K stacks

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Date:	Mon, 7 Jul 2014 16:52:35 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: fallout of 16K stacks

On Mon, Jul 7, 2014 at 4:04 PM, Andi Kleen <andi@...stfloor.org> 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
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