On Wed 24-08-16 10:15:02, Joonsoo Kim wrote: > On Tue, Aug 23, 2016 at 05:38:08PM +0200, Michal Hocko wrote: > > On Tue 23-08-16 11:13:03, Joonsoo Kim wrote: > > > On Thu, Aug 18, 2016 at 01:52:19PM +0200, Michal Hocko wrote: > > [...] > > > > I am not opposing the patch (to be honest it is quite neat) but this > > > > is buggering me for quite some time. Sorry for hijacking this email > > > > thread but I couldn't resist. Why are we trying to optimize SLAB and > > > > slowly converge it to SLUB feature-wise. I always thought that SLAB > > > > should remain stable and time challenged solution which works reasonably > > > > well for many/most workloads, while SLUB is an optimized implementation > > > > which experiment with slightly different concepts that might boost the > > > > performance considerably but might also surprise from time to time. If > > > > this is not the case then why do we have both of them in the kernel. It > > > > is a lot of code and some features need tweaking both while only one > > > > gets testing coverage. So this is mainly a question for maintainers. Why > > > > do we maintain both and what is the purpose of them. > > > > > > I don't know full history about it since I joined kernel communitiy > > > recently(?). Christoph would be a better candidate for this topic. > > > Anyway, > > > > > > SLAB if SLUB beats SLAB completely. But, there are fundamental > > > differences in implementation detail so they cannot beat each other > > > for all the workloads. It is similar with filesystem case that various > > > filesystems exist for it's own workload. > > > > Do we have any documentation/study about which particular workloads > > benefit from which allocator? It seems that most users will use whatever > > the default or what their distribution uses. E.g. SLES kernel use SLAB > > because this is what we used to have for ages and there was no strong > > reason to change that default. From such a perspective having a stable > > allocator with minimum changes - just bug fixes - makes a lot of sense. > > It doesn't make sense to me. Even if someone uses SLAB due to > conventional reason, they would want to use shiny new feature and get > performance improvement. > > And, it is not only reason to use SLAB. There would be many different > reasons to use SLAB. Could you be more specific please? Are there any inherent problems that would make one allocator unsuitable for specific workloads? > > I remember Mel doing some benchmarks when "why opensuse kernels do not > > use the default SLUB allocator" came the last time and he didn't see any > > large winner there > > https://lists.opensuse.org/opensuse-kernel/2015-08/msg00098.html > > This set of workloads is of course not comprehensive to rule one or > > other but I am wondering whether there are still any pathological > > workloads where we really want to keep SLAB or add new features to it. > > AFAIK, some network benchmark still shows regression in SLUB. > > http://lkml.kernel.org/r/20150907113026.5bb28ca3@xxxxxxxxxx That suggests that this is not an inherent problem of SLUB though. -- Michal Hocko SUSE Labs -- 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>