On Mon, 30 Mar 2015 18:49:06 -0400 Milosz Tanski <milosz@xxxxxxxxx> wrote: > > A fincore+pread solution that blocks is simply unsafe > > to use for us. We'll have to stay with the threadpool :-(. > > We're getting data from a network filesystem Ceph in our case, but it > could be pNFS. In many cases those filesystems have some kind > hierarchy and it's not uncommon for us to se requests that take 20 to > 25 milliseconds to complete. In this case the miss becomes very > expensive. And it's not just that one requests experiences the slow > down all the request being serviced by that (single) epoll thread > experience head-of-line blocking because of one stalled request. > > 10K request a second is a common load for many web services / video > servers servings chunks of data. If we experience one miss a second, > that 25 million stall will impact 250 other requests (all of them will > have a 25ms latency tacked on). I'd expect a fincore() which doesn't do SetPageReferenced() to be orders of magnitude better than this. A fincore() which does use SetPageReferenced() will be in the "basically never happens" region - it would take massive and artificial memory stress to trigger. -- 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
