On Fri 12-04-19 09:32:55, Yafang Shao wrote: > On Thu, Apr 11, 2019 at 11:10 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > On Thu 11-04-19 21:54:22, Yafang Shao wrote: > > > On Thu, Apr 11, 2019 at 9:39 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > On Thu 11-04-19 20:41:32, Yafang Shao wrote: > > > > > On Thu, Apr 11, 2019 at 8:27 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > > > > > On Thu 11-04-19 19:59:51, Yafang Shao wrote: > > > > > > > The current item 'pgscan' is for pages in the memcg, > > > > > > > which indicates how many pages owned by this memcg are scanned. > > > > > > > While these pages may not scanned by the taskes in this memcg, even for > > > > > > > PGSCAN_DIRECT. > > > > > > > > > > > > > > Sometimes we need an item to indicate whehter the tasks in this memcg > > > > > > > under memory pressure or not. > > > > > > > So this new item allocstall is added into memory.stat. > > > > > > > > > > > > We do have memcg events for that purpose and those can even tell whether > > > > > > the pressure is a result of high or hard limit. Why is this not > > > > > > sufficient? > > > > > > > > > > > > > > > > The MEMCG_HIGH and MEMCG_LOW may not be tiggered by the tasks in this > > > > > memcg neither. > > > > > They all reflect the memory status of a memcg, rather than tasks > > > > > activity in this memcg. > > > > > > > > I do not follow. Can you give me an example when does this matter? I > > > > > > For example, the tasks in this memcg may encounter direct page reclaim > > > due to system memory pressure, > > > meaning it is stalling in page alloc slow path. > > > At the same time, maybe there's no memory pressure in this memcg, I > > > mean, it could succussfully charge memcg. > > > > And that is exactly what those events aim for. They are measuring > > _where_ the memory pressure comes from. > > > > Can you please try to explain what do you want to achieve again? > > To know the impact of this memory pressure. > The current events can tell us the source of this pressure, but can't > tell us the impact of this pressure. Can you give me a more specific example how you are going to use this counter in a real life please? -- Michal Hocko SUSE Labs
