Messages in this thread | | | Date | Thu, 17 Apr 2008 09:34:50 -0700 | From | "Paul Menage" <> | Subject | Re: [Fwd: [-mm] Add an owner to the mm_struct (v9)] |
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On Thu, Apr 17, 2008 at 4:30 AM, Oleg Nesterov <oleg@tv-sign.ru> wrote: > > > > I had this loop earlier (inspired from zap_threads()), is this loop more > > efficient than what we have? > > All sub-threads have the same ->mm. Once we see that c->mm != mm, we don't > need to waste CPU iterating over the all other threads in the thread group.
Technically they don't have to have the same mm, right? You can use CLONE_THREAD without CLONE_VM when creating a new subthread.
So the complete loop is required for correctness - but it might make sense to include your version of the loop first, since that will be faster whenever there are heavily-threaded apps on the system, and will give the right answer 99.9% of the time (i.e. except when the user is doing something really weird with clone flags).
> chance you have the "for dummies" explanation what mm->owner is? > I mean, I can't understand how it is possible that 2 CLONE_VM tasks > are not equal wrt "ownering".
The idea is to be able to get from an mm to a task, where that task is representative of the tasks using the mm. Uses include:
- virtual address space cgroup - when we extend an mm, we don't always have a task pointer available currently.
- swap cgroup - when swapping from an mm, find a task whose swap cgroup we can charge the swap page to
- revokeat() - apparently needs this for locating tasks based on file mappings
> When the old owner dies, we choose a > random thread with the same mm. But we do nothing when the last user > of ->mm dies. What is the point? (please feel free to ignore my q
When the last user of the mm dies, the mm is freed, so there's no need for mm->owner to be valid any longer.
Paul
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