On Fri 03-08-18 14:59:34, Zhaoyang Huang wrote: > On Fri, Aug 3, 2018 at 2:18 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > On Fri 03-08-18 14:11:26, Zhaoyang Huang wrote: > > > On Fri, Aug 3, 2018 at 1:48 PM Zhaoyang Huang <huangzhaoyang@xxxxxxxxx> wrote: > > > > > > > > for the soft_limit reclaim has more directivity than global reclaim, we40960 > > > > have current memcg be skipped to avoid potential page thrashing. > > > > > > > The patch is tested in our android system with 2GB ram. The case > > > mainly focus on the smooth slide of pictures on a gallery, which used > > > to stall on the direct reclaim for over several hundred > > > millionseconds. By further debugging, we find that the direct reclaim > > > spend most of time to reclaim pages on its own with softlimit set to > > > 40960KB. I add a ftrace event to verify that the patch can help > > > escaping such scenario. Furthermore, we also measured the major fault > > > of this process(by dumpsys of android). The result is the patch can > > > help to reduce 20% of the major fault during the test. > > > > I have asked already asked. Why do you use the soft limit in the first > > place? It is known to cause excessive reclaim and long stalls. > > It is required by Google for applying new version of android system. > There was such a mechanism called LMK in previous ANDROID version, > which will kill process when in memory contention like OOM does. I > think Google want to drop such rough way for reclaiming pages and turn > to memcg. They setup different memcg groups for different process of > the system and set their softlimit according to the oom_adj. Their > original purpose is to reclaim pages gentlely in direct reclaim and > kswapd. During the debugging process , it seems to me that memcg maybe > tunable somehow. At least , the patch works on our system. Then the suggestion is to use v2 and the high limit. This is much less disruptive method for pro-active reclaim. Really softlimit semantic is established for many years and you cannot change it even when it sucks for your workload. Others might depend on the traditional behavior. I have tried to change the semantic in the past and there was a general consensus that changing the semantic is just too risky. So it is nice that it helps for your particular workload but this is not an upstream material, I am sorry. -- Michal Hocko SUSE Labs
