Note that you do not want GUP to succeed on device page, i do not see
where that is handled in the new code.

On Sun, Aug 15, 2021 at 1:40 PM John Hubbard [off-list ref] wrote:

On 8/15/21 8:37 AM, Christoph Hellwig wrote:

quoted

quoted

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8ae31622deef..d48a1f0889d1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -1218,7 +1218,7 @@ __maybe_unused struct page *try_grab_compound_head(struct page *page, int refs,
  static inline __must_check bool try_get_page(struct page *page)
  {
     page = compound_head(page);
-    if (WARN_ON_ONCE(page_ref_count(page) <= 0))
+    if (WARN_ON_ONCE(page_ref_count(page) < (int)!is_zone_device_page(page)))

Please avoid the overly long line.  In fact I'd be tempted to just not
bother here and keep the old, more lose check.  Especially given that
John has a patch ready that removes try_get_page entirely.

Yes. Andrew has accepted it into mmotm.

Ralph's patch here was written well before my cleanup that removed
try_grab_page() [1]. But now that we're here, if you drop this hunk then
it will make merging easier, I think.


[1] https://lore.kernel.org/r/20210813044133.1536842-4-jhubbard@nvidia.com (local)

thanks,
--
John Hubbard
NVIDIA