* J. Bruce Fields (bfields@xxxxxxxxxxxx) wrote: > On Mon, Oct 29, 2012 at 11:13:43AM -0400, Mathieu Desnoyers wrote: > > * Linus Torvalds (torvalds@xxxxxxxxxxxxxxxxxxxx) wrote: > > > On Mon, Oct 29, 2012 at 5:42 AM, Mathieu Desnoyers > > > <mathieu.desnoyers@xxxxxxxxxxxx> wrote: > > > > > > > > So defining e.g.: > > > > > > > > #include <linux/log2.h> > > > > > > > > #define DFR_HASH_BITS (PAGE_SHIFT - ilog2(BITS_PER_LONG)) > > > > > > > > would keep the intended behavior in all cases: use one page for the hash > > > > array. > > > > > > Well, since that wasn't true before either because of the long-time > > > bug you point out, clearly the page size isn't all that important. I > > > think it's more important to have small and simple code, and "9" is > > > certainly that, compared to playing ilog2 games with not-so-obvious > > > things. > > > > > > Because there's no reason to believe that '9' is in any way a worse > > > random number than something page-shift-related, is there? And getting > > > away from *previous* overly-complicated size calculations that had > > > been broken because they were too complicated and random, sounds like > > > a good idea. > > > > Good point. I agree that unless we really care about the precise number > > of TLB entries and cache lines used by this hash table, we might want to > > stay away from page-size and pointer-size based calculation. > > > > It might not hurt to explain this in the patch changelog though. > > I'd also be happy to take that as a separate patch now. FYIW: I've made a nice boo-boo above. It should have been: #define DFR_HASH_BITS (PAGE_SHIFT - ilog2(sizeof(struct hlist_head))) Because we happen to have a memory indexed in bytes, not in bits. I guess this goes a long way proving Linus' point about virtues of trivial code. ;-) Thanks, Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
