On Thu 12-06-14 12:17:33, Tejun Heo wrote: > Hello, Michal. > > On Thu, Jun 12, 2014 at 04:22:37PM +0200, Michal Hocko wrote: > > The primary question would be, whether this is is the best transition > > strategy. I do not know how many users apart from developers are really > > using unified hierarchy. I would be worried that we merge a feature which > > will not be used for a long time. > > I'm planning to drop __DEVEL__ mask from the unified hierarchy in a > cycle, at most two. OK, I am obviously behind the current cgroup core changes. I thought that unified hierarchy will be for development only for much more time. > The biggest hold up at the moment is > straightening out the interfaces and interaction between memcg and > blkcg because I think it'd be silly to have to go through another > round of interface versioning effort right after transitioning to > unified hierarchy. I'm not too confident whether it'd be possible to > get blkcg completely in shape by that time, but, if that takes too > long, I'll just leave blkcg behind temporarily. So, at least from > kernel side, it's not gonna be too long. > > There sure is a question of how fast userland will move to the new > interface. Yeah, I was mostly thinking about those who would need to to bigger changes. AFAIR threads will no longer be distributable between groups. > Some are already playing with unified hierarchy and > planning to migrate as soon as possible but there sure will be others > who will take more time. Can't tell for sure, but the thing is that > migration to min/low/high/max scheme is a signficant migration effort > too, so I'm not sure how much we'd gain by doing that separately. > It'd be an extra transition step for userland (optional but still), > more combinations of configration to handle for memcg, and it's not > like unified hierarchy is that difficult to transition to. > > > Moreover, if somebody wants to transition from soft limit then it would > > be really hard because switching to unified hierarchy might be a no-go. > > Why would that be a no-go? I remember discussions about per-thread distributions and some other things missing from the new API. > Its usage is mostly similar with > tranditional hierarchies and can be used with other hierarchies, so > while it'd take some adaptation, in most cases gradual transition > shouldn't be a big problem. OK > > I think that it is clear that we should deprecate soft_limit ASAP. I > > also think it wont't hurt to have min, low, high in both old and unified > > API and strongly warn if somebody tries to use soft_limit along with any > > of the new APIs in the first step. Later we can even forbid any > > combination by a hard failure. > > I don't quite understand how you plan to deprecate it. Sure you can > fail with -EINVAL or whatnot when the wrong combination Yes, I was thinking that direction. First warn and then EINVAL later. > is used but I don't think there's any chance of removing the knob. > There's a reason why we're introducing a new version of the whole > cgroup interface which can co-exist with the existing one after all. > If you wanna version memcg interface separately, maybe that'd work but > it sounds like a lot of extra hassle for not much gain. No, I didn't mean to version the interface. I just wanted to have gradual transition for potential soft_limit users. Maybe I am misunderstanding something but I thought that new version of API will contain all knobs which are not marked .flags = CFTYPE_INSANE while the old API will contain all of them. -- 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>