On 02/24/2017 01:28 PM, Michal Hocko wrote: > 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. No one is arguing that shrinker is not problematic. And would be great if it is removed from lmk. The oom_score_adj is the way user-space tells the kernel what the user-space has as prio. And android is using that very much. It's a core part. I have never seen it be used on other linux system so what is the intended usage of oom_score_adj? Is this really abusing? I think I can help out with removing shrinker from lmk. Not using oom_score_adj is harder and has a bigger impact on android, except the trivial solution by adding replacement oom_user_prio and use that within android and kernel. _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
