linux-kernel - Re: [RFC] mm: generic adaptive large memory allocation APIs

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Date:	Thu, 13 May 2010 13:45:35 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com, akpm@...ux-foundation.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Jiri Slaby <jslaby@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Avi Kivity <avi@...hat.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: [RFC] mm: generic adaptive large memory allocation APIs

Hi

> void *kvmalloc(size_t size)
> {
> 	void *ptr;
> 
> 	if (size < PAGE_SIZE)
> 		return kmalloc(PAGE_SIZE, GFP_KERNEL);
> 	ptr = alloc_pages_exact(size, GFP_KERNEL | __GFP_NOWARN);

low order GFP_KERNEL allocation never fail. then, this doesn't works
as you expected.

> 	if (ptr != NULL)
> 		return ptr;
> 
> 	return vmalloc(size);

On x86, vmalloc area is only 128MB address space. it is very rare 
resource than physical ram. vmalloc fallback is not good idea.


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