Messages in this thread | | | Date | Wed, 26 Mar 2008 04:20:35 -0700 | From | "Paul Menage" <> | Subject | Re: [RFC][-mm] Memory controller add mm->owner |
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On Wed, Mar 26, 2008 at 3:29 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > >> > >> - in the worst case, it's not going to be worse than doing a > >> for_each_thread() loop > >> > > This will have to be the common case, since you never know what combination of > clone calls did CLONE_VM and what did CLONE_THREAD. At exit time, we need to pay > a for_each_process() overhead.
I'm not convinced of this. All we have to do is find some other process p where p->mm == current->mm and make it the new owner. Exactly what sequence of clone() calls was used to cause the sharing isn't really relevant. I really think that a suitable candidate will be found amongst your children or your first sibling in 99.9% of those cases where more than one process is using an mm.
The actual sequence would have to go something like:
static inline bool need_new_owner(struct mm_struct *mm) { return (mm && mm->owner == current && atomic_read(&mm->users) > 1); } static inline void try_give_mm_ownership( struct task_struct *task, struct mm_struct *mm) { if (task->mm != mm) return; task_lock(task); if (task->mm == mm) { mm->owner = task; } task_unlock(task); }
struct mm_struct *mm = current->mm; task_lock(current); current->mm = NULL; task_unlock(current);
/* First try my children */ if (need_new_owner(mm)) { for_each_child(current, c) { try_give_mm_ownership(c); if (!need_new_owner(mm)) break; } }
/* Then try my siblings */ if (need_new_owner(mm)) { for_each_child(current->real_parent, c) { try_give_mm_ownership(c); if (!need_new_owner(mm)) break; } }
if (need_new_owner(mm)) { /* We'll almost never get here */ for_each_process(p) { try_give_mm_ownership(p); if (!need_new_owner(mm)) break; } }
Paul
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