On Fri, Jul 12, 2013 at 09:31:42AM -0700, Dave Hansen wrote: > On 07/10/2013 11:12 PM, Joonsoo Kim wrote: > > On Wed, Jul 10, 2013 at 10:38:20PM -0700, Dave Hansen wrote: > >> You're probably right for small numbers of pages. But, if we're talking > >> about things that are more than, say, 100 pages (isn't the pcp batch > >> size clamped to 128 4k pages?) you surely don't want to be doing > >> buffered_rmqueue(). > > > > Yes, you are right. > > Firstly, I thought that I can use this for readahead. On my machine, > > readahead reads (maximum) 32 pages in advance if faulted. And batch size > > of percpu pages list is close to or larger than 32 pages > > on today's machine. So I didn't consider more than 32 pages before. > > But to cope with a request for more pages, using rmqueue_bulk() is > > a right way. How about using rmqueue_bulk() conditionally? > > How about you test it both ways and see what is faster? It is not easy to test which one is better, because a difference may be appeared on certain circumstances only. Do not grab the global lock as much as possible is preferable approach to me. > > > Hmm, rmqueue_bulk() doesn't stop until all requested pages are allocated. > > If we request too many pages (1024 pages or more), interrupt latency can > > be a problem. > > OK, so only call it for the number of pages you believe allows it to > have acceptable interrupt latency. If you want 200 pages, and you can > only disable interrupts for 100 pages, then just do it in two batches. > > The point is that you want to avoid messing with the buffering by the > percpu structures. They're just overhead in your case. Okay. Thanks. > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>