On Wed, 07 Jun 2006 10:26:03 +0100
Andy Whitcroft <[email protected]> wrote:
> > btw Andy, that UNALIGNED_ZONE_BOUNDARIES message is useless. Only 0.1% of
> > users even have the knowledge how to recompile their kernel, let alone the
> > inclination. Can we do something smarter here?
>
> Yes, valid point there. The overall plan is that this should never come
> out as the option should be on unless the architecture is ensuring
> alignment. Right now the only architecture which is so marked is x86.
> I wonder if we should also be tainting the kernel at that point so its
> obvious to 'us' that a kernel has this problem?
Better to make things just work if we can.
> The other option is to just turn the check on all the time. It is two
> shift and mask + a compare on two cache lines that we definatly are
> examining anyhow to make the merge checks.
Sounds OK to me.
Note that the code can be optimised:
if (page_zone_id(page) != page_zone_id(buddy))
...
static inline int page_zone_id(struct page *page)
{
return (page->flags >> ZONETABLE_PGSHIFT) & ZONETABLE_MASK;
}
We don't need to perform the shift to make that comparison. If the
compiler's sufficiently smart it will be able to optimise that for us.
<checks>
shrl $30, %edx #, <variable>.flags
shrl $30, %eax #, <variable>.flags
cmpl %eax, %edx # <variable>.flags, <variable>.flags
Nope, not smart enough.
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