[Linux-ia64] Re: [RFC] NUMA functions for accessing replicated areas

On Sat, 19 Jan 2002 18:27:48 +0100, 
Andrea Arcangeli <andrea@suse.de> wrote:
>On Sat, Jan 19, 2002 at 11:25:17AM +1100, Keith Owens wrote:
>The opaque void * spread across all the API looks rather scary.
>Furthmore I'm not convinced we need to pass any cookie to the api, all
>the calls knows the numadata info by the static status after boot.
>
>So I think something like this should be enough:
>
>	int numa_replicated(unsigned long address, int size);
>	int numa_getarea(void *to, unsigned long from, int size);
>	int numa_putarea(unsigned long to, void *from, int size);

That assumes that all replicated data is identical.  It starts off that
way but what prevents one set of replicated data being changed and not
the others?  I don't mind that assumption, it makes life easier for kdb,
but I did not want to constrain NUMA implementations.  However if
everyone agrees that each instance of replcated data should always be
identical then numa_getarea() can read from any instance and
numa_putarea() writes to all instances, no need for numa_replicate_loop.

>Futhmore it may be even better to drop numa_replicated completly and to
>default using numa_getarea/numa_putarea always, this should make kdb
>even cleaner. Implementation of getarea/putarea for non numa case will
>be a simple memcpy.

If numa_replicated() returns true then it is safe to use memcpy, if
numa_replicated() is omitted then the get/put functions must validate
the from address on get and the to address on put.  kdb v2.1 relies on
the MMU via __copy_to_user() to detect invalid user supplied addresses.