Messages in this thread | | | Date | Fri, 02 Apr 2004 16:15:15 +0200 | From | Zoltan Menyhart <> | Subject | Re: To kunmap_atomic or not to kunmap_atomic ? |
| |
Hugh Dickins wrote: > > 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
As you have *map* - *unmap* macros / functions, they give a _hint_ that the original intention of the author was to allow some architectures - which do need some resources to map things - manage these resources. See:
static inline void *kmap(struct page *page) #define kunmap(page)
#define kmap_atomic(page, idx) #define kunmap_atomic(addr, idx) #define kmap_atomic_to_page(ptr)
I think we cannot guarantee that we will never ever need to unmap things. As it is required to use kmap - kunmap in pair, it is quite logic to use kmap_atomic* in pair with kunmap_atomic.
I think it is a bad programming style to abuse the fact that some macros are no-ops for the most popular architectures.
I think we should have some global counters in DEBUG mode which are incremented on each call to *map* and decremented on each *unpap* call, and we can detect, ooops, it leaks...
Regards,
Zoltán Menyhárt - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |