svn commit: r218966 - head/sys/vm

Kostik Belousov kostikbel at
Sun Feb 27 13:19:10 UTC 2011

On Sun, Feb 27, 2011 at 11:12:03PM +1100, Bruce Evans wrote:
> On Sun, 27 Feb 2011, Bruce Cran wrote:
> >On Thu, 2011-02-24 at 10:36 +1100, Bruce Evans wrote:
> >>
> >>I would cast operand(s) in the expression as necessary to prevent overflow
> >>of subexpressions.  vm_pindex_t would work, but I prefer to use a type
> >>related to the subexpressions.  Not sure what that is.  Maybe just
> >>uintmax_t for safety (even that is not safe if the subexpressions have
> >>large values).  So:
> >>
> >>     (uintmax_t)swap_bcount * SWAP_META_PAGES * n / mumble.
> >
> >Following Alan's suggestion, I've attached an updated patch which uses a
> >cast to u_long and returns long.
> I thought he only meant to return long.  The units being returned are
> PAGE_SIZE smaller than the units in the expression.  But I don't know
> exacty how large swp_bcount can be.  If everything fits in a single
> object, then vm_size_t = u_int on 32-bit machines is enough.

I think that return type should be left as vm_offset_t. The calculation
basically returns some quantity of type vm_offset_t, divided by PAGE_SIZE.
This validates the new return type.

The calculation could use vm_offset_t, or uintmax_t cast, probably
vm_offset_t is preferred for the same reason.
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