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

David Rientjes
2013-04-17T04:47:21Z

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?