linux-kernel - Re: Calling free_pages on part of the memory returned by get_free

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Date:	Thu, 24 Apr 2008 14:32:03 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: Calling free_pages on part of the memory returned by get_free_pages?

Andi Kleen wrote:

> It is ok, as long as you don't use compound pages (__GFP_COMP) and call
> split_page() to fix up the reference counts.

Thanks.  I've never even heard of compound pages, so that's not a problem.  I'll
look up split_page().

> Also you do this to save memory right? 

Yes, I expect to allocate a 5MB chunk of memory, which means I'll be wasting 3MB
of physically-contiguous memory on an embedded system.

> The large system hash code does it too

Ah, I see that in alloc_large_system_hash().  Thanks

> If it's reasonably common we should re-add alloc/get_pages_exact() helper to 
> make this pattern clear and easier to use.

I'd be in favor of that!  I was planning on doing something like that anyway.

-- 
Timur Tabi
Linux kernel developer at Freescale
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