On Mon, 2019-09-30 at 14:51 -0700, John Hubbard wrote: > On 9/27/19 4:40 PM, Leonardo Bras wrote: > > As decribed, gup_pgd_range is a lockless pagetable walk. So, in order to > > monitor against THP split/collapse with the couting method, it's necessary > > s/couting/counting/ >
Thanks, fixed for v5. > > to bound it with {start,end}_lockless_pgtbl_walk. > > > > There are dummy functions, so it is not going to add any overhead on archs > > that don't use this method. > > > > Signed-off-by: Leonardo Bras <leona...@linux.ibm.com> > > --- > > mm/gup.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/mm/gup.c b/mm/gup.c > > index 98f13ab37bac..7105c829cf44 100644 > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -2325,6 +2325,7 @@ static bool gup_fast_permitted(unsigned long start, > > unsigned long end) > > int __get_user_pages_fast(unsigned long start, int nr_pages, int write, > > struct page **pages) > > { > > + struct mm_struct *mm; > > I don't think that this local variable adds any value, so let's not use it. > Similar point in a few other patches too. It avoids 1 deference of current->mm, it's a little performance gain. > > > unsigned long len, end; > > unsigned long flags; > > int nr = 0; > > @@ -2352,9 +2353,12 @@ int __get_user_pages_fast(unsigned long start, int > > nr_pages, int write, > > > > if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && > > gup_fast_permitted(start, end)) { > > + mm = current->mm; > > + start_lockless_pgtbl_walk(mm); > > local_irq_save(flags); > > gup_pgd_range(start, end, write ? FOLL_WRITE : 0, pages, &nr); > > local_irq_restore(flags); > > + end_lockless_pgtbl_walk(mm); > > } > > > > return nr; > > @@ -2404,6 +2408,7 @@ int get_user_pages_fast(unsigned long start, int > > nr_pages, > > unsigned int gup_flags, struct page **pages) > > { > > unsigned long addr, len, end; > > + struct mm_struct *mm; > > Same here. > > > int nr = 0, ret = 0; > > > > if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM))) > > @@ -2421,9 +2426,12 @@ int get_user_pages_fast(unsigned long start, int > > nr_pages, > > > > if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && > > gup_fast_permitted(start, end)) { > > + mm = current->mm; > > + start_lockless_pgtbl_walk(mm); > > Minor: I'd like to rename this register_lockless_pgtable_walker(). > > > local_irq_disable(); > > gup_pgd_range(addr, end, gup_flags, pages, &nr); > > local_irq_enable(); > > + end_lockless_pgtbl_walk(mm); > > ...and deregister_lockless_pgtable_walker(). > I have no problem changing the name, but I don't register/deregister are good terms for this. I would rather use start/finish, begin/end, and so on. Register sounds like something more complicated than what we are trying to achieve here. > > thanks, Thank you!
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