On Mon, Aug 09, 2004 at 10:25:31PM -0700, Paul Jackson wrote:

While I'm here, the statement that only the highest zone is policied
actually applies only to MPOL_BIND, right?  The comment that asserts

That is correct. I can add a comment.

 1) Change the man page wording, for each of get_mempolicy(2), mbind(2),
    and set_mempolicy(2), to boldly state:

	Beware:
		Pass in a value of maxnode that is * one more * than the
		number of nodes represented in nodemask.  If for example,
		nodemask represents 64 nodes, numbered 0 to 63, pass in a
		value of 65 for maxnodes.

Yes, I will clarify the manpages.

I see no problem with hardcoding 8 bits per byte. 

 2) Review, test, fix, and apply as fixed the following patch.  For extra
    credit, get rid of the hard coded 8, 32 and 64 values in the compat stuff,
    visible in the patch below.  I compiled the patch, once, on an ia64.
    Otherwise totally untested.

    This patch:
	a) Notes the situation in a prominent "==> Beware <==".
	b) Consistently decrements maxnode immediately on each system call
	   entry (where someone reading the code might best notice).
	c) Otherwise treats maxnode consistently within the code.
	d) Addresses the MPOL_BIND max policy only comment.
	e) Addresses the harcoded numbers 64 and 8 in copy_nodes_to_user().

Yes, the 64 should be addressed agreed. That came from a misguided
attempt by me to not require compat_* functions (by making the 32bit
and 64bit ABI be the same), but that didn't work out.

    Yes - it's ugly.  The time that will be lost by those who try to use
    this interface directly will be ugly too.

 3) Could you propose a strategy for fixing this?  It might take a couple

The only way would be to allocate new system call slots for the 
two calls. But I'm not convinced it is worth it.

Sorry, but I don't want to break binary compatibility. 

If it was really that bad you should have complained earlier (the
code was out long enough for review), now it is too late.

If
   you have to tell me that SGI has to put in a workaround for a year, on
   any machine with _exactly_ 2049 nodes, such as padding the user nodemask
   up to 2050 nodes, I'm prepared to deal with that <grin>.

There are many more users of these calls than SGI. And most of them are
using libnuma, which you are proposing to break. 


-Andi
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