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Subject: Re: [PATCH] fs: use kmalloc() to allocate fdmem if possible
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Avi Kivity <avi@redhat.com>, Changli Gao <xiaosuo@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>, jslaby@suse.cz,
       akpm@linux-foundation.org, paulmck@linux.vnet.ibm.com,
       adobriyan@gmail.com, mingo@elte.hu, peterz@infradead.org,
       linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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Date: Mon, 03 May 2010 11:13:52 +0200
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Le lundi 03 mai 2010 à 11:49 +0300, Avi Kivity a écrit :

> A kmalloc()ed page is virtually contiguous, satisfying your requirement.
> 

Still, a different function pair is needed, at least for documentation
reasons.

Changli, _many_ patches like yours were suggested and refused in the
past for the reason it should be generic. Maybe its time...

So first introduce a pair of funtions, then we can use them.

At free time we can use is_vmalloc_addr() so that no extra bit is needed
to tell if a zone was vmalloced() or kmalloced()


One remark :

+       data = kmalloc(size, GFP_KERNEL);

If allocation fails (because of fragmentation), we would have a kernel
log.
Still, vmalloc() might be OK.
So you should add a __GFP_NOWARN flag.




/*
 * Warning: if size is not a power of two, kmalloc() might
 * waste memory because of its requirements.
 */
void *kvmalloc(size_t size)
{
	void *ptr = kmalloc(size, GFP_KERNEL | __GFP_NOWARN);

	if (ptr)
		return ptr;
	return vmalloc(size);
}

void kvfree(void *ptr)
{
	BUG_ON(in_interrupt());
	if (is_vmalloc_addr(ptr))
		vfree(ptr);
	else
		kfree(ptr);
}