On Thu, 3 Sep 2015 20:51:09 -0700 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, Sep 3, 2015 at 8:26 PM, Dave Chinner <dchinner@xxxxxxxxxx> wrote: > > > > The double standard is the problem here. No notification, proof, > > discussion or review was needed to turn on slab merging for > > everyone, but you're setting a very high bar to jump if anyone wants > > to turn it off in their code. > > Ehh. You realize that almost the only load that is actually seriously > allocator-limited is networking? > > And slub was beating slab on that? And slub has been doing the merging > since day one. Slab was just changed to try to keep up with the > winning strategy. Sorry, I have to correct you on this. The slub allocator is not as fast as you might think. The slab allocator is actually faster for networking. IP-forwarding, single CPU, single flow UDP (highly tuned): * Allocator slub: 2043575 pps * Allocator slab: 2088295 pps Difference slab faster than slub: * +44720 pps and -10.48ns The slub allocator have a faster "fastpath", if your workload is fast-reusing within the same per-cpu page-slab, but once the workload increases you hit the slowpath, and then slab catches up. Slub looks great in micro-benchmarking. As you can see in patchset: [PATCH 0/3] Network stack, first user of SLAB/kmem_cache bulk free API. http://thread.gmane.org/gmane.linux.kernel.mm/137469/focus=376625 I'm working on speeding up slub to the level of slab. And it seems like I have succeeded with half-a-nanosec 2090522 pps (+2227 pps or 0.51 ns). And with "slab_nomerge" I get even high performance: * slub: bulk-free and slab_nomerge: 2121824 pps * Diff to slub: +78249 and -18.05ns -- Best regards, Jesper Dangaard Brouer MSc.CS, Sr. Network Kernel Developer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
