# \[PATCH 3/6\] struct page: add field for vm\_struct

- From: Matthew Wilcox \<willy@infradead.org\>
- Date: 2018-02-11 21:16:46 
- List: linux-security-module
- Page: https://ratatoskr.run/linux-security-module/2018/02/5197193
- Thread: https://ratatoskr.run/linux-security-module/2018/02/5197191/t.md

```text
On Sun, Feb 11, 2018 at 05:19:17AM +0200, Igor Stoppa wrote:
> The struct page has a "mapping" field, which can be re-used, to store a
> pointer to the parent area. This will avoid more expensive searches.
> 
> As example, the function find_vm_area is reimplemented, to take advantage
> of the newly introduced field.

Umm.  Is it more efficient?  You're replacing an rb-tree search with a
page-table walk.  You eliminate a spinlock, which is great, but is the
page-table walk more efficient?  I suppose it'll depend on the depth of
the rb-tree, and (at least on x86), the page tables should already be
in cache.

Unrelated to this patch, I'm working on a patch to give us page_type,
and I think I'll allocate a bit to mark pages which are vmalloced.
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