Re: [PATCH] vmap(): don't allow invalid pages

[Matthew Wilcox]

On Thu, Jan 20, 2022 at 09:07:11AM +0530, Anshuman Khandual wrote:
> 
> 
> On 1/19/22 10:52 PM, Yury Norov wrote:
> >> Why should not this just scan over the entire user provided struct page
> >> array and make sure that all pages there in are valid via above method,
> >> but in vmap() itself before calling vmap_pages_range(). Because seems
> >> like a single invalid page detected in vmap_pages_pte_range() will
> >> anyways abort the entire vmap(). This will also enable us to drop the
> >> existing NULL check above.
> >
> > I can do this, but why is it any better than the current approach?
> 
> Because it will just return on the first instance where the valid page
> check fails, saving us some CPU cycles and an incomplete mapping ?

The valid page check is never intended to fail!  If you're worried about
the efficiency of doing this, you have seriously confused your priorities.