On Fri 24-02-17 13:19:46, peter enderborg wrote: > On 02/23/2017 09:36 PM, Martijn Coenen wrote: > > On Thu, Feb 23, 2017 at 9:24 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote: > >> So, just for context, Android does have a userland LMK daemon (using > >> the mempressure notifiers) as you mentioned, but unfortunately I'm > >> unaware of any devices that ship with that implementation. > > I've previously worked on enabling userspace lmkd for a previous > > release, but ran into some issues there (see below). > > > >> This is reportedly because while the mempressure notifiers provide a > >> the signal to userspace, the work the deamon then has to do to look up > >> per process memory usage, in order to figure out who is best to kill > >> at that point was too costly and resulted in poor device performance. > > In particular, mempressure requires memory cgroups to function, and we > > saw performance regressions due to the accounting done in mem cgroups. > > At the time we didn't have enough time left to solve this before the > > release, and we reverted back to kernel lmkd. > > > >> So for shipping Android devices, the LMK is still needed. However, its > >> not critical for basic android development, as the system will > >> function without it. > > It will function, but it most likely will perform horribly (as the > > page cache will be trashed to such a level that the system will be > > unusable). > > > >> Additionally I believe most vendors heavily > >> customize the LMK in their vendor tree, so the value of having it in > >> staging might be relatively low. > >> > >> It would be great however to get a discussion going here on what the > >> ulmkd needs from the kernel in order to efficiently determine who best > >> to kill, and how we might best implement that. > > The two main issues I think we need to address are: > > 1) Getting the right granularity of events from the kernel; I once > > tried to submit a patch upstream to address this: > > https://lkml.org/lkml/2016/2/24/582 > > 2) Find out where exactly the memory cgroup overhead is coming from, > > and how to reduce it or work around it to acceptable levels for > > Android. This was also on 3.10, and maybe this has long been fixed or > > improved in more recent kernel versions. > > > > I don't have cycles to work on this now, but I'm happy to talk to > > whoever picks this up on the Android side. > I sent some patches that is different approach. It still uses shrinkers > but it has a kernel part that do the kill part better than the old one > but it does it the android way. The future for this is get it triggered > with other path's than slab shrinker. But we will not continue unless > we get google-android to be part of it. Hocko objected heavy on > the patches but seems not to see that we need something to > do the job before we can disconnect from shrinker. Yeah, I strongly believe that the chosen approach is completely wrong. Both in abusing the shrinker interface and abusing oom_score_adj as the only criterion for the oom victim selection. -- Michal Hocko SUSE Labs _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
