On Wed, Jan 20, 2021 at 8:19 AM Jason Gunthorpe [off-list ref] wrote:

On Tue, Jan 19, 2021 at 08:43:31PM -0500, Pavel Tatashin wrote:

quoted

When pages are longterm pinned, we must migrated them out of movable zone.
The function that migrates them has a hidden loop with goto. The loop is
to retry on isolation failures, and after successful migration.

Make this code better by moving this loop to the caller.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
 mm/gup.c | 88 +++++++++++++++++++++++---------------------------------
 1 file changed, 36 insertions(+), 52 deletions(-)

This looks OK, it is better

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

I really dislike we always have to go over the page list twice in pin
mode

I agree, I also dislike that we have to loop twice.

The is_pinnable_page() and LRU isolation should really be done inside
__get_user_pages_locked() as each page is added to the output list

But that is more of a larger issue than this series

We could also think about adding some optimization flags, i.e. clients
could tell gup that the pinned memory content can be discarded
FOLL_DISCARD. That way we could always allocate new pages in the right
zones as we do with this series and free existing translations. No
migration check would be necessary with such a flag.

Jason