On Thu, Jan 7, 2021 at 7:16 PM Michal Hocko [off-list ref] wrote:

On Thu 07-01-21 10:52:21, Muchun Song wrote:

quoted

On Thu, Jan 7, 2021 at 12:13 AM Michal Hocko [off-list ref] wrote:

quoted

On Wed 06-01-21 16:47:34, Muchun Song wrote:

quoted

If the refcount is one when it is migrated, it means that the page
was freed from under us. So we are done and do not need to migrate.

Is this common enough that it would warrant the explicit check for each
migration?

Are you worried about the overhead caused by the check? Thanks.

I am not as worried as I would like to see some actual justification for
this optimization.

OK. The HugeTLB page can be freed after it was isolated but before
being migrated. Right? If we catch this case, it is an optimization.
I do this just like unmap_and_move() does for a base page.

--
Michal Hocko
SUSE Labs