On Thu 14-04-22 10:25:29, Yosry Ahmed wrote: > On Fri, Apr 8, 2022 at 1:08 PM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > > > > On Fri, Apr 8, 2022 at 7:55 AM Dan Schatzberg <schatzberg.dan@xxxxxxxxx> wrote: > > > > > > On Fri, Apr 08, 2022 at 04:11:05PM +0200, Michal Hocko wrote: > > > > Regarding "max" as a possible input. I am not really sure to be honest. > > > > I can imagine that it could be legit to simply reclaim all the charges > > > > (e.g. before removing the memcg) which should be achieveable by > > > > reclaiming the reported consumption. Or what exactly should be the > > > > semantic? > > > > > > Yeah, it just allows you to avoid reading memory.current to just > > > reclaim everything if you can specify "max" - you're still protected > > > by nretries to eventually bail out. Mostly, though I just feel like > > > supporting "max" makes memory.reclaim semetric with a lot of the > > > cgroup memory control files which tend to support "max". > > > > One possible approach here is to have force_empty behavior when we > > write "max" to memory.reclaim. From Google's perspective we don't have > > a preference, but it seems to me like logical behavior. We can do this > > either by directly calling mem_cgroup_force_empty() or just draining > > stock and lrus in memory_reclaim(). > > > > This actually brings up another interesting point. Do you think we > > should drain lrus if try_to_free_mem_cgroup_pages() fails to reclaim > > the request amount? We can do this after the first call or before the > > last one. It could introduce more evictable pages for > > try_to_free_mem_cgroup_pages() to free. > > Hey Michal, any thoughts on this? I am looking for feedback on this > before I send out v4. As I've already said I do not have strong preferences for the "max" value to be accepted by the interface. Maybe you can add a support for max in a separate patch so the discussion would not delay the rest of the work. For the LRU draining I do not see any problem for that to be added. The overhead of the operation would increase, especially on larger machines, which could be a concern. So the real question is whether not doing so is a big problem. Our force_empty implementation optimistically drains pcp caches but please note that this is not really guranteeing anything as charges can happen at any time. -- Michal Hocko SUSE Labs
