On Mon 15-01-18 15:53:35, Andrey Ryabinin wrote: > > > On 01/15/2018 03:46 PM, Michal Hocko wrote: > > On Mon 15-01-18 15:30:59, Andrey Ryabinin wrote: > >> > >> > >> On 01/12/2018 03:24 PM, Michal Hocko wrote: > >>> On Fri 12-01-18 00:59:38, Andrey Ryabinin wrote: > >>>> On 01/11/2018 07:29 PM, Michal Hocko wrote: > >>> [...] > >>>>> I do not think so. Consider that this reclaim races with other > >>>>> reclaimers. Now you are reclaiming a large chunk so you might end up > >>>>> reclaiming more than necessary. SWAP_CLUSTER_MAX would reduce the over > >>>>> reclaim to be negligible. > >>>>> > >>>> > >>>> I did consider this. And I think, I already explained that sort of race in previous email. > >>>> Whether "Task B" is really a task in cgroup or it's actually a bunch of reclaimers, > >>>> doesn't matter. That doesn't change anything. > >>> > >>> I would _really_ prefer two patches here. The first one removing the > >>> hard coded reclaim count. That thing is just dubious at best. If you > >>> _really_ think that the higher reclaim target is meaningfull then make > >>> it a separate patch. I am not conviced but I will not nack it it either. > >>> But it will make our life much easier if my over reclaim concern is > >>> right and we will need to revert it. Conceptually those two changes are > >>> independent anywa. > >>> > >> > >> Ok, fair point. But what about livelock than? Don't you think that we should > >> go back to something like in V1 patch to prevent it? > > > > I am not sure what do you mean by the livelock here. > > > > Livelock is when tasks in cgroup constantly allocate reclaimable memory at high rate, > and user asked to set too low unreachable limit e.g. 'echo 4096 > memory.limit_in_bytes'. OK, I wasn't sure. The reclaim target, however, doesn't have a direct influence on this, though. > We will loop indefinitely in mem_cgroup_resize_limit(), because try_to_free_mem_cgroup_pages() != 0 > (as long as cgroup tasks generate new reclaimable pages fast enough). I do not thing this is a real problem. The context is interruptible and I would even consider it safer to keep retrying than simply failing prematurely. My experience tells me that basically any hard coded retry loop in the kernel is wrong. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
