To memcg maintainer, Could you comment about this topic?
On Fri, Mar 17, 2017 at 04:16:35PM -0700, Tim Murray wrote: > Hi all, > > I've been working to improve Android's memory management and drop > lowmemorykiller from the kernel, and I'd like to get some feedback on a small > patch with a lot of side effects. > > Currently, when an Android device is under memory pressure, one of three > things will happen from kswapd: > > 1. Compress an anonymous page to ZRAM. > 2. Evict a file page. > 3. Kill a process via lowmemorykiller. > > The first two are cheap and per-page, the third is relatively cheap in the > short term, frees many pages, and may cause power and performance penalties > later on when the process has to be started again. For lots of reasons, I'd > like a better balance between reclamation and killing on Android. > > One of the nice things about Android from an optimization POV is that the > execution model is more constrained than a generic Linux machine. There are > only a limited number of processes that need to execute quickly for the > device to appear to have good performance, and a userspace daemon (called > ActivityManagerService) knows exactly what those processes are at any given > time. We've made use of that in the past via cpusets and schedtune to limit > the CPU resources available to background processes, and I think we can apply > the same concept to memory. > > This patch adds a new tunable to mem cgroups, memory.priority. A mem cgroup > with a non-zero priority will not be eligible for scanning until the > scan_control's priority is greater than zero. Once the mem cgroup is eligible > for scanning, the priority acts as a bias to reduce the number of pages that > should be scanned. > > We've seen cases on Android where the global LRU isn't sufficient. For > example, notifications in Android are rendered as part of a separate process > that runs infrequently. However, when a notification appears and the user > slides down the notification tray, we'll often see dropped frames due to page > faults if there has been severe memory pressure. There are similar issues > with other persistent processes. > > The goal on an Android device is to aggressively evict from very low-priority > background tasks that are likely to be killed anyway, since this will reduce > the likelihood of lowmemorykiller running in the first place. It will still > evict some from foreground and persistent processes, but it should help > ensure that background processes are effectively reduced to the size of their > heaps before evicting from more critical tasks. This should mean fewer > background processes end up killed, which should improve performance and > power on Android across the board (since it costs significantly less to page > things back in than to replay the entirety of application startup). > > The follow-on that I'm also experimenting with is how to improve vmpressure > such that userspace can have some idea when low-priority memory cgroups are > about as small as they can get. The correct time for Android to kill a > background process under memory pressure is when there is evidence that a > process has to be killed in order to alleviate memory pressure. If the device > is below the low memory watermark and we know that there's probably no way to > reclaim any more from background processes, then a userspace daemon should > kill one or more background processes to fix that. Per-cgroup priority could > be the first step toward that information. > > I've tested a version of this patch on a Pixel running 3.18 along with an > overhauled version of lmkd (the Android userspace lowmemorykiller daemon), > and it does seem to work fine. I've ported it forward but have not yet > rigorously tested it at TOT, since I don't have an Android test setup running > TOT. While I'm getting my tests ported over, I would like some feedback on > adding another tunable as well as what the tunable's interface should be--I > really don't like the 0-10 priority scheme I have in the patch but I don't > have a better idea. > > Thanks, > Tim > > Tim Murray (1): > mm, memcg: add prioritized reclaim > > include/linux/memcontrol.h | 20 +++++++++++++++++++- > mm/memcontrol.c | 33 +++++++++++++++++++++++++++++++++ > mm/vmscan.c | 3 ++- > 3 files changed, 54 insertions(+), 2 deletions(-) > > -- > 2.12.0.367.g23dc2f6d3c-goog > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majord...@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"d...@kvack.org";> em...@kvack.org </a>
