linux-kernel - Re: [Bisected Regression in 2.6.35] A full tmpfs filesystem causeshibernation to hang

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Date:	Fri, 3 Sep 2010 03:07:33 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	"M. Vefa Bicakci" <bicave@...eronline.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-pm@...ts.linux-foundation.org,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [Bisected Regression in 2.6.35] A full tmpfs filesystem causeshibernation to hang

On Friday, September 03, 2010, KOSAKI Motohiro wrote:
> Hello,
> 
> > > > > Like in the patch below, perhaps?
> > > > 
> > > > Looks like fine. but I have one question. hibernate_preallocate_memory() call
> > > > preallocate_image_memory() two times. Why do you only care latter one?
> > > > former one seems similar risk.
> > > 
> > > The first one is mandatory, ie. if we can't allocate the requested number of
> > > pages at this point, we fail the entire hibernation.  In that case the
> > > performance hit doesn't matter.
> > 
> > IOW, your patch at http://lkml.org/lkml/2010/9/2/262 is still necessary to
> > protect against the infinite loop in that case.
> 
> As far as I understand, we need distinguish two allocation failure.
>   1) failure because no enough memory
> 	-> yes, hibernation should fail
>  2) failure because already allocated enough lower zone memory
> 	-> why should we fail?
> 
> If the system has a lot of memory, scenario (2) is happen frequently than (1).
> I think we need check alloc_highmem and alloc_normal variable and call
> preallocate_image_highmem() again instead preallocate_image_memory()
> if we've alread allocated enough lots normal memory.
> 
> nit?

Actually I thought about that, but we don't really see hibernation fail for
this reason.  In all of the tests I carried out the requested 50% of highmem
had been allocated before allocations from the normal zone started to be
made, even if highmem was 100% full at that point.  So this appears to be
a theoretical issue and covering it would require us to change the algorithm
entirely (eg. it doesn't make sense to call preallocate_highmem_fraction() down
the road if that happens).

Thanks,
Rafael
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