linux-kernel - Re: [PATCH 04/12] mm: alloc_contig_freed

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Message-ID: <1301610411.30870.29.camel@nimitz>
Date:	Thu, 31 Mar 2011 15:26:51 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-media@...r.kernel.org,
	linux-mm@...ck.org, Kyungmin Park <kyungmin.park@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ankita Garg <ankita@...ibm.com>,
	Daniel Walker <dwalker@...eaurora.org>,
	Johan MOSSBERG <johan.xx.mossberg@...ricsson.com>,
	Mel Gorman <mel@....ul.ie>, Pawel Osciak <pawel@...iak.com>
Subject: Re: [PATCH 04/12] mm: alloc_contig_freed_pages() added

On Fri, 2011-04-01 at 00:18 +0200, Michal Nazarewicz wrote:
> On Thu, 31 Mar 2011 23:14:38 +0200, Dave Hansen wrote:
> > We BUG_ON() in bootmem.  Basically if we try to allocate an early-boot
> > structure and fail, we're screwed.  We can't keep running without an
> > inode hash, or a mem_map[].
> >
> > This looks like it's going to at least get partially used in drivers, at
> > least from the examples.  Are these kinds of things that, if the driver
> > fails to load, that the system is useless and hosed?  Or, is it
> > something where we might limp along to figure out what went wrong before
> > we reboot?
> 
> Bug in the above place does not mean that we could not allocate memory.  It
> means caller is broken.

Could you explain that a bit?

Is this a case where a device is mapped to a very *specific* range of
physical memory and no where else?  What are the reasons for not marking
it off limits at boot?  I also saw some bits of isolation and migration
in those patches.  Can't the migration fail?  

-- Dave

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