On Fri, Sep 20, 2019 at 06:10:11AM +0900, Suleiman Souhlal wrote: > On Fri, Sep 20, 2019 at 1:22 AM Roman Gushchin <guro@xxxxxx> wrote: > > > > On Thu, Sep 19, 2019 at 10:39:18PM +0900, Suleiman Souhlal wrote: > > > On Fri, Sep 6, 2019 at 6:57 AM Roman Gushchin <guro@xxxxxx> wrote: > > > > The patchset has been tested on a number of different workloads in our > > > > production. In all cases, it saved hefty amounts of memory: > > > > 1) web frontend, 650-700 Mb, ~42% of slab memory > > > > 2) database cache, 750-800 Mb, ~35% of slab memory > > > > 3) dns server, 700 Mb, ~36% of slab memory > > > > > > Do these workloads cycle through a lot of different memcgs? > > > > Not really, those are just plain services managed by systemd. > > They aren't restarted too often, maybe several times per day at most. > > > > Also, there is nothing fb-specific. You can take any new modern > > distributive (I've tried Fedora 30), boot it up and look at the > > amount of slab memory. Numbers are roughly the same. > > Ah, ok. > These numbers are kind of surprising to me. > Do you know if the savings are similar if you use CONFIG_SLAB instead > of CONFIG_SLUB? I did only a brief testing of the SLAB version: savings were there, numbers were slightly less impressive, but still in a double digit number of percents. > > > > For workloads that don't, wouldn't this approach potentially use more > > > memory? For example, a workload where everything is in one or two > > > memcgs, and those memcgs last forever. > > > > > > > Yes, it's true, if you have a very small and fixed number of memory cgroups, > > in theory the new approach can take ~10% more memory. > > > > I don't think it's such a big problem though: it seems that the majority > > of cgroup users have a lot of them, and they are dynamically created and > > destroyed by systemd/kubernetes/whatever else. > > > > And if somebody has a very special setup with only 1-2 cgroups, arguably > > kernel memory accounting isn't such a big thing for them, so it can be simple > > disabled. Am I wrong and do you have a real-life example? > > No, I don't have any specific examples. > > -- Suleiman
