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

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Date:	Wed, 17 Apr 2013 15:46:02 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.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

Hi David,

2013/04/17 13:47, David Rientjes wrote:
> 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.

O.K. I'll update it.

>
>> 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.

I think so, too.

> How much memory are we talking about?

Hmm. I don't know correctly.

Here is kernel message of my system. The message is shown by mem_init().

-- 
Memory: 30491076k/33554432k available (5570k kernel code, 2274228k absent, 789128k reserved, 5667k data, 1784k init)
---

Reserved memroy size is 789128k. So part of them is freed after system boot
by  memory hotplug  et al.

Thanks,
Yasuaki Ishimatsu


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