On Fri 28-06-13 08:54:35, Minchan Kim wrote: > Hello Michal, > > On Thu, Jun 27, 2013 at 06:11:03PM +0200, Michal Hocko wrote: > > On Fri 28-06-13 00:35:28, Minchan Kim wrote: > > > Hi Michal, > > > > > > On Thu, Jun 27, 2013 at 11:37:21AM +0200, Michal Hocko wrote: > > > > On Thu 27-06-13 15:12:10, Hyunhee Kim wrote: > > > > > In vmpressure, the pressure level is calculated based on the ratio > > > > > of how many pages were scanned vs. reclaimed in a given time window. > > > > > However, there is a possibility that "scanned < reclaimed" in such a > > > > > case, when reclaiming ends by fatal signal in shrink_inactive_list. > > > > > So, with this patch, we just return "low" level when "scanned < reclaimed" > > > > > happens not to have userland miss reclaim activity. > > > > > > > > Hmm, fatal signal pending on kswapd doesn't make sense to me so it has > > > > to be a direct reclaim path. Does it really make sense to signal LOW > > > > when there is probably a big memory pressure and somebody is killing the > > > > current allocator? > > > > > > So, do you want to trigger critical instead of low? > > > > > > Now, current is going to die so we can expect shortly we can get a amount > > > of memory, normally. > > > > And also consider that this is per-memcg interface. And so it is even > > more complicated. If a task dies then there is _no_ guarantee that there > > will be an uncharge in that group (task could have been migrated to that > > group so the memory belongs to somebody else). > > Good point and that's one of the reason I hate memcg for just using > vmpressure. Well, the very same problem is present in the memcg OOM as well. oom score calculation is not memcg aware wrt charges. > Let's think over it. One of the very avaialbe scenario > which userland could do when notified from vmpressure is that manager > process sends signal for others to release own cached memory. Assuming those processes are in the same memcg, right? > If we use vmpressure without move_charge_at_immigrate in multiple memcg > group, it would be a disaster. But if we use move_charge_at_immigrate, > we will see long stall easily so it's not an option, either. I am not sure I am following you here. Could you be more specific what is the actual problem? >From my POV, a manager can see a memory pressure, it notifies others in the same memcg and they will release their caches. With move_charge_at_immigrate == 0 some of those might release a memory in other group but somebody must be using memory from the currently signaled group, right? > So, IMO, it's not a good idea to use vmpressure with no-root memcg so > it could raise the question again "why vmpressure is part of memcg". Maybe I do not see the problem correctly, but making vmpressure memcg aware was a good idea. It is something like userspace pre-oom handling. > I really didn't want it. :( [...] -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>