On Thu, Aug 23 2012, Glauber Costa wrote: > On 08/23/2012 03:23 AM, Greg Thelen wrote: >> On Wed, Aug 22 2012, Glauber Costa wrote: >> >>>>>> >>>>>> I am fine with either, I just need a clear sign from you guys so I don't >>>>>> keep deimplementing and reimplementing this forever. >>>>> >>>>> I would be for make it simple now and go with additional features later >>>>> when there is a demand for them. Maybe we will have runtimg switch for >>>>> user memory accounting as well one day. >>>>> >>>>> But let's see what others think? >>>> >>>> In my use case memcg will either be disable or (enabled and kmem >>>> limiting enabled). >>>> >>>> I'm not sure I follow the discussion about history. Are we saying that >>>> once a kmem limit is set then kmem will be accounted/charged to memcg. >>>> Is this discussion about the static branches/etc that are autotuned the >>>> first time is enabled? >>> >>> No, the question is about when you unlimit a former kmem-limited memcg. >>> >>>> The first time its set there parts of the system >>>> will be adjusted in such a way that may impose a performance overhead >>>> (static branches, etc). Thereafter the performance cannot be regained >>>> without a reboot. This makes sense to me. Are we saying that >>>> kmem.limit_in_bytes will have three states? >>> >>> It is not about performance, about interface. >>> >>> Michal says that once a particular memcg was kmem-limited, it will keep >>> accounting pages, even if you make it unlimited. The limits won't be >>> enforced, for sure - there is no limit, but pages will still be accounted. >>> >>> This simplifies the code galore, but I worry about the interface: A >>> person looking at the current status of the files only, without >>> knowledge of past history, can't tell if allocations will be tracked or not. >> >> In the current patch set we've conflating enabling kmem accounting with >> the kmem limit value (RESOURCE_MAX=disabled, all_other_values=enabled). >> >> I see no problem with simpling the kernel code with the requirement that >> once a particular memcg enables kmem accounting that it cannot be >> disabled for that memcg. >> >> The only question is the user space interface. Two options spring to >> mind: >> a) Close to current code. Once kmem.limit_in_bytes is set to >> non-RESOURCE_MAX, then kmem accounting is enabled and cannot be >> disabled. Therefore the limit cannot be set to RESOURCE_MAX >> thereafter. The largest value would be something like >> RESOURCE_MAX-PAGE_SIZE. An admin wondering if kmem is enabled only >> has to cat kmem.limit_in_bytes - if it's less than RESOURCE_MAX, then >> kmem is enabled. >> > > If we need to choose between them, I like this better than your (b). > At least it is all clear, and "fix" the history problem, since it is > possible to look up the status of the files and figure it out. > >> b) Or, if we could introduce a separate sticky kmem.enabled file. Once >> set it could not be unset. Kmem accounting would only be enabled if >> kmem.enabled=1. >> >> I think (b) is clearer. >> > Depends on your definition of clearer. We had a knob for > kmem_independent in the beginning if you remember, and it was removed. > The main reason being knobs complicate minds, and we happen to have a > very natural signal for this. I believe the same reasoning applies here. Sounds good to me, so let's go with (a). -- 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>