On Thu, May 06, 2021 at 11:42:59PM -0700, John Hubbard wrote: > > +#define MMF_HAS_PINNED 28 /* FOLL_PIN has run, never cleared */ > > How about this instead, so that we effectively retain the comment block > that is otherwise being deleted from mm.h: > > /* > * MMF_HAS_PINNED: Whether this mm has pinned any pages. This can be either > * replaced in the future by mm.pinned_vm when it becomes stable, or grow into a > * counter on its own. We're aggresive on this bit for now: even if the pinned > * pages were unpinned later on, we'll still keep this bit set for the lifecycle > * of this mm, just for simplicity. > */ > #define MMF_HAS_PINNED 28 /* FOLL_PIN ran. Never cleared. */ Sure, good to know the comment is still valid! > > @@ -1292,8 +1292,8 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm, > > BUG_ON(*locked != 1); > > } > > - if (flags & FOLL_PIN && !atomic_read(&mm->has_pinned)) > > - atomic_set(&mm->has_pinned, 1); > > + if (flags & FOLL_PIN && !test_bit(MMF_HAS_PINNED, &mm->flags)) > > + set_bit(MMF_HAS_PINNED, &mm->flags); > > I expect this suggestion to be controversial, but I'm going to float it > anyway. The above is a little less clear than it used to be, *and* it is > in two places so far, so how about factoring out a tiny subroutine, like this: Definitely less "controversial" than expected, isn't it? ;) Thanks for the suggestion, it looks much better indeed. Also I'll rename the helper to mm_set_has_pinned_flag() as suggested by Matthew. -- Peter Xu
