Messages in this thread | | | Date | Thu, 9 Oct 2014 12:50:37 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/4] mm: gup: add get_user_pages_locked and get_user_pages_unlocked |
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On Wed, Oct 01, 2014 at 10:56:35AM +0200, Andrea Arcangeli wrote:
> +static inline long __get_user_pages_locked(struct task_struct *tsk, > + struct mm_struct *mm, > + unsigned long start, > + unsigned long nr_pages, > + int write, int force, > + struct page **pages, > + struct vm_area_struct **vmas, > + int *locked, > + bool notify_drop) > +{
> + if (notify_drop && lock_dropped && *locked) { > + /* > + * We must let the caller know we temporarily dropped the lock > + * and so the critical section protected by it was lost. > + */ > + up_read(&mm->mmap_sem); > + *locked = 0; > + } > + return pages_done; > +}
> +long get_user_pages_locked(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + int write, int force, struct page **pages, > + int *locked) > +{ > + return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force, > + pages, NULL, locked, true); > +}
> +long get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + int write, int force, struct page **pages) > +{ > + long ret; > + int locked = 1; > + down_read(&mm->mmap_sem); > + ret = __get_user_pages_locked(tsk, mm, start, nr_pages, write, force, > + pages, NULL, &locked, false); > + if (locked) > + up_read(&mm->mmap_sem); > + return ret; > +}
> long get_user_pages(struct task_struct *tsk, struct mm_struct *mm, > unsigned long start, unsigned long nr_pages, int write, > int force, struct page **pages, struct vm_area_struct **vmas) > { > + return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force, > + pages, vmas, NULL, false); > }
I'm wondering about that notify_drop parameter, what's the added benefit? If you look at these 3 callers we can do away with it, since in the second called where we have locked but !notify_drop we seem to do the exact same thing afterwards anyway.
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