On Thu, Jan 10, 2019 at 04:43:57AM -0700, William Kucharski wrote:
>
>
> > On Jan 9, 2019, at 8:08 PM, Yu Zhao <yuz...@google.com> wrote:
> >
> > find_get_pages_range() and find_get_pages_range_tag() already
> > correctly increment reference count on head when seeing compound
> > page, but they may still use page index from tail. Page index
> > from tail is always zero, so these functions don't work on huge
> > shmem. This hasn't been a problem because, AFAIK, nobody calls
> > these functions on (huge) shmem. Fix them anyway just in case.
> >
> > Signed-off-by: Yu Zhao <yuz...@google.com>
> > ---
> > mm/filemap.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 81adec8ee02c..cf5fd773314a 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -1704,7 +1704,7 @@ unsigned find_get_pages_range(struct address_space
> > *mapping, pgoff_t *start,
> >
> > pages[ret] = page;
> > if (++ret == nr_pages) {
> > - *start = page->index + 1;
> > + *start = xas.xa_index + 1;
> > goto out;
> > }
> > continue;
> > @@ -1850,7 +1850,7 @@ unsigned find_get_pages_range_tag(struct
> > address_space *mapping, pgoff_t *index,
> >
> > pages[ret] = page;
> > if (++ret == nr_pages) {
> > - *index = page->index + 1;
> > + *index = xas.xa_index + 1;
> > goto out;
> > }
> > continue;
> > --
>
> While this works, it seems like this would be more readable for future
> maintainers were it to
> instead squirrel away the value for *start/*index when ret was zero on the
> first iteration through
> the loop.
I'm not sure how this could be more readable, and it sounds
independent from the problem the patch fixes.
> Though xa_index is designed to hold the first index of the entry, it seems
> inappropriate to have
> these routines deference elements of xas directly; I guess it depends on how
> opaque we want to keep
> xas and struct xa_state.
It seems to me it's pefectly fine to use fields of xas directly,
and it's being done this way throughout the file.
> Does anyone else have a feeling one way or the other? I could be persuaded
> either way.
