linux-kernel - Re: [Bug fix PATCH v3] Reusing a resource structure allocated by bootmem

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Message-ID: <alpine.DEB.2.02.1304162144320.3493@chino.kir.corp.google.com>
Date:	Tue, 16 Apr 2013 21:47:18 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>, toshi.kani@...com,
	linuxram@...ibm.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [Bug fix PATCH v3] Reusing a resource structure allocated by
 bootmem

On Wed, 17 Apr 2013, Yasuaki Ishimatsu wrote:

> > Why not simply do what generic sparsemem support does by testing
> > PageSlab(virt_to_head_page(res)) and calling kfree() if true and freeing
> > back to bootmem if false?  This should be like a five line patch.
> 
> Is your explanation about free_section_usemap()?
> If so, I don't think we can release resource structure like
> free_section_usemap().

Right, you can't release it like free_section_usemap(), but you're free to 
test for PageSlab(virt_to_head_page(res)) in kernel/resource.c.

> In your explanation case, memmap can be released by put_page_bootmem() in
> free_map_bootmem() since all pages of memmap is used only for memmap.
> But if my understanding is correct, a page of released resource structure
> contain other purpose objects allocated by bootmem. So we cannot
> release resource structure like free_section_usemap().
> 

I'm thinking it would be much easier to just suppress the kfree() if 
!PageSlab.  If you can free an entire page with free_bootmem_late(), 
that would be great, but I'm thinking that will take more work than it's 
worth.  It seems fine to just do free_bootmem() and leave those pages as 
reserved.  How much memory are we talking about?
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