linux-kernel - Re: OOM killer, page fault

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Date:	Mon,  2 Nov 2009 15:59:28 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Norbert Preining <preining@...ic.at>,
	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>
Subject: Re: OOM killer, page fault

> On Mon,  2 Nov 2009 13:24:06 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> 
> > Hi,
> > 
> > (Cc to linux-mm)
> > 
> > Wow, this is very strange log.
> > 
> > > Dear all,
> > > 
> > > (please Cc)
> > > 
> > > With 2.6.32-rc5 I got that one:
> > > [13832.210068] Xorg invoked oom-killer: gfp_mask=0x0, order=0, oom_adj=0
> > 
> > order = 0
> 
> I think this problem results from 'gfp_mask = 0x0'.
> Is it possible?
> 
> If it isn't H/W problem, Who passes gfp_mask with 0x0?
> It's culpit. 
> 
> Could you add BUG_ON(gfp_mask == 0x0) in __alloc_pages_nodemask's head?

No.
In page fault case, gfp_mask show meaningless value. Please ignore it.
pagefault_out_of_memory() always pass gfp_mask==0 to oom.


mm/oom_kill.c
====================================
void pagefault_out_of_memory(void)
{
        unsigned long freed = 0;

        blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
        if (freed > 0)
                /* Got some memory back in the last second. */
                return;

        /*
         * If this is from memcg, oom-killer is already invoked.
         * and not worth to go system-wide-oom.
         */
        if (mem_cgroup_oom_called(current))
                goto rest_and_return;

        if (sysctl_panic_on_oom)
                panic("out of memory from page fault. panic_on_oom is selected.\n");

        read_lock(&tasklist_lock);
        __out_of_memory(0, 0);       <---- here! 
        read_unlock(&tasklist_lock);

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