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SubjectRe: Reduce struct page by 8 bytes on 64bit
On Wed, Apr 16, 2003 at 01:35:39PM -0700, Andrew Morton wrote:
> Matthew Wilcox <> wrote:
> >
> > Jacob's would break if we hashed to different spinlocks. But we don't, we
> > shift right by 8, so we get the same spinlock for atomic things that are on
> > the same "cacheline" (i think PA cachelines are actually 64 or 128 bytes,
> > depending on model).
> >
> Are you prepared to cast this in stone?

I think so. It makes sense to me that we lock an entire cacheline for
this kind of thing. Indeed, locking a smaller amount would probably break
other stuff. Remember set_bit() et al take a pointer to an unsigned long...
but can take a bit number > number of bits in an unsigned long. If anything,
we should maybe expand the range covered by a single lock to a larger amount
than 256 bytes. How big are ext2 bitmaps, for example?

"It's not Hollywood. War is real, war is primarily not about defeat or
victory, it is about death. I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk
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