Re: [LSF/MM TOPIC] Killing reliance on struct page->mapping

[Jerome Glisse <jglisse@redhat.com>]

On Wed, Jan 31, 2018 at 07:09:48PM +0200, Igor Stoppa wrote:
> On 30/01/18 02:43, Jerome Glisse wrote:
> 
> [...]
> 
> > Maybe we can kill page->mapping altogether as a result of this. However this is
> > not my motivation at this time.
> 
> We had a discussion some time ago
> 
> http://www.openwall.com/lists/kernel-hardening/2017/07/07/7
> 
> where you advised to use it for tracking pmalloc pages vs area, which
> generated this patch:
> 
> http://www.openwall.com/lists/kernel-hardening/2018/01/24/7
> 
> Could you please comment what wold happen to the shortcut from struct
> page to vm_struct that this patch is now introducing?

Sadly struct page fields means different thing depending on the context
in which the page is use. This is confusing i know. So when i say kill
page->mapping i am not saying shrink the struct page and remove that
field, i am saying maybe we can kill current user of page->mapping
for regular process page (ie page that are in some mmap() area of a
process).

Other use of that field in different context like yours are not affected
by this change and can ignore it alltogether.

Hope this clarify it :)

Cheers,
Jerome

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