On 8/8/21 11:38 PM, Christoph Hellwig wrote:

On Sun, Aug 08, 2021 at 04:50:17PM -0700, John Hubbard wrote:

quoted

try_grab_page() does the same thing as try_grab_compound_head(...,
refs=1, ...), just with a different API. So there is a lot of code
duplication there.

Change try_grab_page() to call try_grab_compound_head(), while keeping
the API contract identical for callers.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
  mm/gup.c | 29 ++---------------------------
  1 file changed, 2 insertions(+), 27 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 5cb18b62921c..4be6f060fa0b 100644
--- a/mm/gup.c
+++ b/mm/gup.c

@@ -203,33 +203,8 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
   */
  bool __must_check try_grab_page(struct page *page, unsigned int flags)
  {
+	if (flags & (FOLL_GET | FOLL_PIN))
+		return try_grab_compound_head(page, 1, flags) != NULL;
  
  	return true;

Nit: something like:

	if (!(flags & (FOLL_GET | FOLL_PIN)))
		return true;
	return try_grab_compound_head(page, 1, flags) != NULL;

would be a little easier to read.

Really? Well I'll be darned, that's what I wrote in my first draft. And then
I looked at the diffs and thought, "positive logic is clearer, and the diffs
are smaller too", and went with the current version. Which now is apparently
a little worse. oops.

Well, "50-50/90", as we used to say in an earlier job: 50% chance of either
outcome, and due to The Way Things Go, a 90% chance of picking the wrong one!

I can no longer tell which one is easier to read now, so I'll be glad to change
it. :)

thanks,
-- 
John Hubbard
NVIDIA