linux-kernel - Re: [patch 1/2] fix call to alloc_bootmem after bootmem has been freed

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Date:	Wed, 22 Nov 2006 10:23:40 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Andrew Morton <akpm@...l.org>
Cc:	Christian Krafft <krafft@...ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] fix call to alloc_bootmem after bootmem has been freed

On Tuesday 21 November 2006 19:26, Andrew Morton wrote:
> slab is a very different thing from vmalloc.  One could easily envisage
> situations (now or in the future) in which slab is ready, but vmalloc is
> not (more likely vice versa).
> 
> It'd be better to add a new vmalloc_is_available.  (Just an int - no need
> for a helper function).

In the time line, we currently have

start_kernel()
   ...
   setup_arch()
      init_bootmem()              # alloc_bootmem starts working
      ...
      paging_init()               # needed for vmalloc
   ...                            #
   mem_init()
      free_all_bootmem()          # alloc_bootmem stops working, alloc_pages
				  # starts working
   kmem_cache_init()              # kmalloc and vmalloc start working
   ...
   system_state = SYSTEM_RUNNING

The one interesting point here is where you have to transition between
calling alloc_bootmem and calling the regular allocator functions.
Maybe calling it slab_is_available() was not the best choice for a name,
but I don't see a point in having different names for essentially the
same question, "bootmem or not bootmem". The powerpc platform has an
integer variable called 'mem_init_done', which expresses this well
IMHO, but it's currently not portable.

Checking for SYSTEM_RUNNING is obviously the wrong choice, since it is
set at a very late point in bootup, long after bootmem is gone.

	Arnd <><
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