linux-kernel - Re: + x86-mm-handle-mm_fault_error-in-kernel-space.patch added to -mm tree

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Message-ID: <20110312211143.GA27460@redhat.com>
Date:	Sat, 12 Mar 2011 22:11:43 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Vagin <avagin@...il.com>
Cc:	Pavel Emelyanov <xemul@...nvz.org>,
	Andrey Vagin <avagin@...nvz.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, Nick Piggin <npiggin@...e.de>
Subject: Re: + x86-mm-handle-mm_fault_error-in-kernel-space.patch added to
	-mm tree

On 03/11, Oleg Nesterov wrote:
>
> On 03/11, Andrew Vagin wrote:
> >
> >
> The point is, if current was _NOT_ killed we should follow the current
> pagefault_out_of_memory() logic or remove pagefault_out_of_memory()
> completely.

Yes, and I still think this is valid. And thus I still think the patch
should be changed (btw, this problem is not x86 specific).

However,

> >> Why do you think the current task should be killed? In this case we
> >> do not need oom-killer at all, we could always kill the caller of
> >> alloc_page/etc.
> >
> > You don't understand. alloc_page calls oom-killer himself, then try
> > allocate memory again. Pls look at __alloc_pages_slowpath().
> > __alloc_pages_slowpat may fail if order > 3 || gfp_mask & __GFP_NOFAIL
> > || test_thread_flag(TIF_MEMDIE)
>
> Andrew, please, I know this.

Hmm. It turns out I do not ;)

I thought I can find the case when handle_mm_fault() returns VM_FAULT_OOM
and the caller is not killed, but I can't. I do not really understand
mem_cgroup_handle_oom/etc, but it seems we always retry indefinitely even
with mem_cgroup's. mm/hugetlb.c looks fine too...

So, I have to apologize, I am starting to think you are right.



Maybe someone could explain why pagefault_out_of_memory() is still
needed?

Oleg.

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