On 04/23/2013 01:58 PM, Michel Lespinasse wrote: > On Mon, Apr 22, 2013 at 8:54 AM, Michal Hocko <mhocko@xxxxxxx> wrote: >> On Mon 22-04-13 08:46:20, Tejun Heo wrote: >>> Oh, if so, I'm happy. Sorry about being brash on the thread; however, >>> please talk with google memcg people. They have very different >>> interpretation of what "softlimit" is and are using it according to >>> that interpretation. If it *is* an actual soft limit, there is no >>> inherent isolation coming from it and that should be clear to >>> everyone. >> >> We have discussed that for a long time. I will not speak for Greg & Ying >> but from my POV we have agreed that the current implementation will work >> for them with some (minor) changes in their layout. >> As I have said already with a careful configuration (e.i. setting the >> soft limit only where it matters - where it protects an important >> memory which is usually in the leaf nodes) > > I don't like your argument that soft limits work if you only set them > on leaves. To me this is just a fancy way of saying that hierarchical > soft limits don't work. > > Also it is somewhat problematic to assume that important memory can > easily be placed in leaves. This is difficult to ensure when > subcontainer destruction, for example, moves the memory back into the > parent. > Michal, For the most part, I am siding with you in this discussion. But with this only-in-leaves thing, I am forced to flip (at least for this). You are right when you say that in a configuration with A being parent of B and C, A being over its hard limit will affect reclaim in B and C, and soft limits should work the same. However, "will affect reclaim" is a big vague. More specifically, if the sum of B and C's hard limit is smaller or equal A's hard limit, the only way of either B or C to trigger A's hard limit is for them, themselves, to go over their hard limit. *This* is the case you you are breaking when you try to establish a comparison between soft and hard limits - which is, per se, sane. Translating this to the soft limit speech, if the sum of B and C's soft limit is smaller or equal A's soft limit, and one of them is over the soft limit, that one should be reclaimed. The other should be left alone. I understand perfectly fine that soft limit is a best effort, not a guarantee. But if we don't do that, I understand that we are doing effort, not best effort. This would only be attempted in our first pass. In the second pass, we reclaim from whoever. It is also not that hard to do it: Flatten the tree in a list, with the leaves always being placed before the inner nodes. Start reclaiming from nodes over the soft limit, hierarchically. This means that whenever we reach an inner node and it is *still* over the soft limit, we are guaranteed to have scanned their children already. In the case I described, the children over its soft limit would have been reclaimed, without the well behaving children being touched. Now all three are okay. If we reached an inner node and we still have a soft limit problem, then we are effectively talking about the case you have been describing. Reclaim from whoever you want. -- 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>