On Mon 20-06-16 09:13:55, Andy Lutomirski wrote: > On Mon, Jun 20, 2016 at 6:36 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Fri 17-06-16 13:00:42, Andy Lutomirski wrote: > >> If CONFIG_VMAP_STACK is selected, kernel stacks are allocated with > >> vmalloc_node. > > > > I like this! It also reduces demand for higher order (order-2) pages > > considerably which is a great plus on its own. I would be little bit > > worried about the performance because vmalloc wasn't the fastest one > > AFAIR. Have you tried to measure that? > > It seems to add about 1.5µs to pthread_create+join on my laptop. (On > an unmodified, stripped-down kernel, it took about 7µs before. On a > Fedora system, the baseline is much worse.) I think that most of the > overhead is because vmalloc allocates one page at a time, which means > that it won't use a higher order page even if one is sitting on a > freelist. I guess a less artificial test case which would would generate a lot of tasks and some memory pressure would be more representative (e.g. kernbench). The thing is that even order-2 pages might get quite expensive when the memory is fragmented. > I can imagine better integration with the page allocator in which > higher order pages are used if readily available. Similarly, vfree > could free pages that happen to be aligned and consecutive as a unit > to avoid the overhead of merging them back together one at a time. > > But I'm not planning on doing any of this myself any time soon. I > just want to get the code working and merged. I agree, there is a room for improvement but no necessarily as a part of this series. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
