From mboxrd@z Thu Jan  1 00:00:00 1970
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [RFC] mm: generic adaptive large memory allocation APIs
Date: Thu, 13 May 2010 13:45:35 +0900 (JST)
Message-ID: <20100513134124.2164.A69D9226@jp.fujitsu.com>
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Cc: kosaki.motohiro@jp.fujitsu.com, akpm@linux-foundation.org,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Jiri Slaby <jslaby@suse.cz>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Ingo Molnar <mingo@elte.hu>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Avi Kivity <avi@redhat.com>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Changli Gao <xiaosuo@gmail.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

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.