On 08/24/2012 09:06 AM, Greg Thelen wrote: > 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). > Michal, what do you think ? -- 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>