On Thu, Mar 31, 2022 at 7:35 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Thu 31-03-22 19:18:58, Zhaoyang Huang wrote: > > On Thu, Mar 31, 2022 at 5:01 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > On Thu 31-03-22 16:00:56, zhaoyang.huang wrote: > > > > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> > > > > > > > > For some kind of memcg, the usage is varies greatly from scenarios. Such as > > > > multimedia app could have the usage range from 50MB to 500MB, which generated > > > > by loading an special algorithm into its virtual address space and make it hard > > > > to protect the expanded usage without userspace's interaction. > > > > > > Do I get it correctly that the concern you have is that you do not know > > > how much memory your workload will need because that depends on some > > > parameters? > > right. such as a camera APP will expand the usage from 50MB to 500MB > > because of launching a special function(face beauty etc need special > > algorithm) > > > > > > > Furthermore, fixed > > > > memory.low is a little bit against its role of soft protection as it will response > > > > any system's memory pressure in same way. > > > > > > Could you be more specific about this as well? > > As the camera case above, if we set memory.low as 200MB to keep the > > APP run smoothly, the system will experience high memory pressure when > > another high load APP launched simultaneously. I would like to have > > camera be reclaimed under this scenario. > > OK, so you effectivelly want to keep the memory protection when there is > a "normal" memory pressure but want to relax the protection on other > high memory utilization situations? > > How do you exactly tell a difference between a steady memory pressure > (say stream IO on the page cache) from "high load APP launched"? Should > you reduce the protection on the stram IO situation as well? We can take either system's io_wait or PSI_IO into consideration for these. > > [...] > > > One very important thing that I am missing here is the overall objective of this > > > tuning. From the above it seems that you want to (ab)use memory->low to > > > protect some portion of the charged memory and that the protection > > > shrinks over time depending on the the global PSI metrict and time. > > > But why this is a good thing? > > 'Good' means it meets my original goal of keeping the usage during a > > period of time and responding to the system's memory pressure. For an > > android like system, memory is almost forever being in a tight status > > no matter how many RAM it has. What we need from memcg is more than > > control and grouping, we need it to be more responsive to the system's > > load and could sacrifice its usage under certain criteria. > > Why existing tools/APIs are insufficient for that? You can watch for > both global and memcg memory pressure including PSI metrics and update > limits dynamically. Why is it necessary to put such a logic into the > kernel? Poll and then React method in userspace requires a polling interval and response time. Take PSI as an example, it polls ten times during POLLING_INTERVAL while just report once, which introduce latency in some extend. > > -- > Michal Hocko > SUSE Labs
