Hello, Kent. On Tue, Aug 20, 2013 at 07:31:51PM -0700, Kent Overstreet wrote: > All this for a performance improvement of 10x to 50x (or more), for the > ida sizes I measured.
That's misleading, isn't it? We should see large performance improvements even without the large pages. What matters more is the leaf node performance for vast majority of cases and an extra radix tree layer on top would cover most of whatever is left. Whether to use high order pages or not only affects the extreme niche use cases and I don't think going for high order pages to micro optimize those extreme use cases is the right trade off. > So I could see your point if we were allocating gobs of vmalloc memory, > or high order allocations big enough to realistically be problematic (I > honestly don't think these will be) - but to me, this seems like a > pretty reasonable tradeoff for those performance gains. The trade off is made up as the bulk of the performance benefit can be gained without resorting to high order allocations. > (And the performance gains do substantially come from using more > contiguous memory and treating the whole data structure as an array, and > doing less pointer chasing/looping) I really have hard time buying that. Let's say you go with single page leaf node and an extra single page layer on top. How many IDs are we talking about? For the cases which are most performance sensitive, this doesn't even matter a bit as percpu caching layer would be on top anyway. I really don't think the micro optimization is called for at the cost of high order allocations from low level tool library. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
