Messages in this thread | | | Date | Wed, 16 Apr 2003 22:26:51 +0100 | From | Matthew Wilcox <> | Subject | Re: Reduce struct page by 8 bytes on 64bit |
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On Wed, Apr 16, 2003 at 01:35:39PM -0700, Andrew Morton wrote: > Matthew Wilcox <willy@debian.org> 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?
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