Re: [RFC] Tight check of pfn_valid on sparsemem

[Russell King - ARM Linux]

On Tue, Jul 13, 2010 at 03:04:00PM +0900, Minchan Kim wrote:
> > __get_user() works with TLB and page table, the vaddr is really mapped or not.
> > If you got SEGV, __get_user() returns -EFAULT. It works per page granule.

Not in kernel space.  It works on 1MB sections there.

Testing whether a page is mapped by __get_user is a hugely expensive
way to test whether a PFN is valid.  It'd be cheaper to use our
flatmem implementation of pfn_valid() instead.
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