Re: To kunmap_atomic or not to kunmap_atomic ?

[Hugh Dickins]

On Thu, 1 Apr 2004, Zoltan Menyhart wrote:
> I can see a couple of functions, like
> 
> static inline struct mm_struct * ptep_to_mm(pte_t * ptep)
> {
> 	struct page * page = kmap_atomic_to_page(ptep);
> 	return (struct mm_struct *) page->mapping;
> }
> 
> in "rmap.?" without invoking "kunmap_atomic()".
> Is it intentional?
> What if for an architecture "kunmap_atomic()" is not a no-op ?

Amusing misunderstanding.  Take a look at kmap_atomic_to_page
in arch/i386/mm/highmem.c: it doesn't _do_ a kmap_atomic, it
translates the virtual address already supplied by kmap_atomic
to the address of the struct page of the physical page backing
that virtual address.  So, in the case of try_to_unmap_one, it
operates on the virtual address supplied by rmap_ptep_map
(which does do a kmap_atomic), and at the end there's an
rmap_ptep_unmap (which does the rmap_ptep_unmap).

Hugh

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