linux-kernel - Re: [PATCH -tip] x86: uv - prevent NULL dereference in uv_system

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Date:	Sun, 3 May 2009 02:09:50 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Jack Steiner <steiner@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] x86: uv - prevent NULL dereference in
 uv_system_init

On Sun, 3 May 2009, Ingo Molnar wrote:

> Hm, would be nice if we had a __GFP_PANIC variant in kmalloc that 
> would just panic straight in the allocator, when allocation failure 
> is not acceptable. (Andrew Cc:-ed)
> 
> It does not increase the priority of the allocation nor does it 
> trigger any 'dont fail' logic - it is simply the central expression 
> of 'this should not have failed, panic'.
> 

SLUB stores two new slab allocation orders: the cache's adjustable order 
which is calculated at kmem_cache_create(), and the smallest order that 
can accommodate at least one object allocation.  The latter is used as a 
fallback when the former fails in the page allocator.

So for __GFP_PANIC to work in this case, it could not be implemented in 
the page allocator (SLUB also passes __GFP_NORETRY for new slabs) but 
rather above it in allocate_slab().  It would then be a no-op for 
alloc_pages().
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