On Fri, Aug 12, 2022 at 12:13:09PM +1000, Alistair Popple wrote:
> When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages()
> is called to migrate pages out of zones which should not contain any
> longterm pinned pages.
>
> When migration succeeds all pages will have been unpinned so pinning
> needs to be retried. Migration can also fail, in which case the pages
> will also have been unpinned but the operation should not be retried. If
> all pages are in the correct zone nothing will be unpinned and no retry
> is required.
>
> The logic in check_and_migrate_movable_pages() tracks unnecessary state
> and the return codes for each case are difficult to follow. Refactor the
> code to clean this up. No behaviour change is intended.
>
> Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
>
> ---
This seems like the cleanest version yet!
> +static long check_and_migrate_movable_pages(unsigned long nr_pages,
> + struct page **pages)
> +{
> + int ret;
> + unsigned long collected;
> + LIST_HEAD(movable_page_list);
> +
> + collected = collect_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages);
> + if (!collected)
> + return 0;
> +
> + ret = migrate_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages);
> + if (!ret)
> + return -EAGAIN;
> + else
> + return ret;
I would drop the else path and just return zero
Arguably migrate_longterm_unpinnable_pages() should do the same?
> @@ -2051,10 +2079,10 @@ static long __gup_longterm_locked(struct mm_struct *mm,
> break;
>
> rc = check_and_migrate_movable_pages(rc, pages);
> - } while (!rc);
> + } while (rc == -EAGAIN);
Since the only reader only cares about errno or not errno..
But no biggie either way
Thanks,
Jason
