On Sun, 2005-08-28 at 18:35 -0700, Andrew Morton wrote: > > Well ... It's my opinion (and purely unsubstantiated, I suppose) that > > it's more efficient on 32 bit platforms to do bit operations on 32 bit > > quantities, which is why I changed the radix tree map shift to 5 for > > that case. > > > > It also makes much cleaner code than having to open code checks on > > variable sized bitmaps.
> It does make the tree higher and hence will incur some more cache missing > when descending the tree. Actually, I don't think it does: the common user is the page tree. Obviously, I've changed nothing on 64 bits, so we only need to consider what I've done on 32 bits. A page size is almost universally 4k on 32 bit, so we need 20 bits to store the page tree index. Regardless of whether the index size is 5 or 6, that gives a radix tree depth of 4. > We changed the node size a few years back. umm.... > http://www.ussg.iu.edu/hypermail/linux/kernel/0206.2/0141.html Yes, but that was to reduce the index size from 7 to 6 for slab allocation reasons. I've just reduced it to 5 on 32 bit. > It would be a little bit sad to be unable to make such tuning adjustments > in the future. Not a huge loss, but a loss. Well .. OK .. If the benchmarks say I've slowed us down on 32 bits, I'll put the variable sizing back in the tag array. James - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
