On Wed 07-10-15 00:58:20, Andrew Morton wrote: > On Wed, 7 Oct 2015 09:30:02 +0200 Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > On Tue 06-10-15 12:22:25, Andrew Morton wrote: > > > On Tue, 6 Oct 2015 19:01:23 +0200 Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > On Mon 05-10-15 14:44:22, Shaohua Li wrote: > > > > > The page_counter_memparse() returns pages for the threshold, while > > > > > mem_cgroup_usage() returns bytes for memory usage. Convert the threshold > > > > > to bytes. > > > > > > > > > > Looks a regression introduced by 3e32cb2e0a12b69150 > > > > > > > > Yes. This suggests > > > > Cc: stable # 3.19+ > > > > > > But it's been this way for 2 years and nobody noticed it. How come? > > > > Maybe we do not have that many users of this API with newer kernels. > > Either it's zero or all the users have worked around this bug. > > > > Or at least, nobody reported it. Maybe people *have* noticed it, and > > > adjusted their userspace appropriately. In which case this patch will > > > cause breakage. > > > > I dunno, I would rather have it fixed than keep bug to bug compatibility > > because they would eventually move to a newer kernel one day when they > > see the "breakage" anyway. > > They'd only see breakage if we fixed this in the newer kernel. > > We could just change the docs and leave it as-is. That it is called > "usage_in_bytes" makes that a bit awkward. The whole API is bytes based. Having one which is silently page size based is definitely wrong. > A bit of googling indicates that people are using usage_in_bytes. A > few. All the discussions I found clearly predate this bug. > > > So did people just stop using this? To be honest I haven't seen any real users from my enterprise distribution experience and I also consider the API quite unusable because most loads simply fill up their limit with the page case so something like a vmpressure is a much better indicator of the memory usage. This has been introduced before my time. Kirill has introduced it back in 2009. > Is there some alternative way of getting the same info? I am not aware of any alternative nor am I aware of any strong usecases for such a small granularity API. The consensus so far has been that any new controller knob for the new cgrroup API has to be backed by a strong usecase. I am pretty sure that we want some form of memory pressure notification, though. > Why does memcg_write_event_control() says "DO NOT USE IN NEW FILES" > and "DO NOT ADD NEW FILES"? Because eventfd notification mechanism is considered a wrong API to convey notifications. New cgroup API is supposed to use a new mechanism. The current one will have to live with the old/legacy cgroup API though. -- 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>