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11:28:46AM +0200, Michal Hocko wrote: >>> >>>> But thinking about this some more, this would be racy same as the >>>> PF_EXITING check. This is not my area but is this performance sensitive >>>> path that couldn't live with the proper find_lock_task_mm? >>> >>> find_lock_task_mm() seems eminently unsuitable for accounting -- >>> iterating the task group is insane. >>> >>> Looking at this, the mm_struct lifetimes suck.. task_struct reference >>> doesn't help, rcu doesn't help :-( >>> >>> Also, whatever the solution it needs to be inside this count_memcg_*() >>> nonsense, because nobody wants this overhead, esp. not for something >>> daft like accounting. >>> >>> My primary desire at this point is to just revert the patch that caused >>> this. Accounting just isn't worth it. Esp. not since there is already a >>> tracepoint in this path -- people that want to count crap can very well >>> get their numbers from that. >> >> I would tend to agree with this. Doing the accounting race free on a >> remote task is nasty and if this is a rare event that could be avoided >> then it should be just dropped than racy and oops prone. >> > > OK, Michal and Peter, > how about keeping the per task schedstat and drop the memcg statistics? > The user can still get the per task information without having to filter > the ftrace log. > I agree. The other parts, schedstat and vmstat, are still quite helpful. Also tracepoints are more expensive than counters once enabled, I think that's too much for just counting numbers. Libo > thanks, > Chenyu