On Sun 22-03-20 21:57:07, Pingfan Liu wrote:
> For zone_device, migration can only happen on is_device_private_page(page).
> Correct the logic in try_to_unmap_one().
Maybe it is just me lacking knowledge in the zone_device ZOO. But
this really deserves a much more detailed explanation IMHO. It seems
a5430dda8a3a ("mm/migrate: support un-addressable ZONE_DEVICE page in
migration") deliberately made the decision to allow unmapping these
pages? Is the check just wrong, inncomplete? Why?
What is the real user visible problem here?
> Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
> Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Aneesh Kumar <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> To: linux-mm@xxxxxxxxx
> ---
> mm/rmap.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index b838647..ffadf3e 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1380,7 +1380,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>
> if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
> is_zone_device_page(page) && !is_device_private_page(page))
> - return true;
> + return false;
>
> if (flags & TTU_SPLIT_HUGE_PMD) {
> split_huge_pmd_address(vma, address,
> @@ -1487,7 +1487,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>
> if (IS_ENABLED(CONFIG_MIGRATION) &&
> (flags & TTU_MIGRATION) &&
> - is_zone_device_page(page)) {
> + is_device_private_page(page)) {
> swp_entry_t entry;
> pte_t swp_pte;
>
> --
> 2.7.5
--
Michal Hocko
SUSE Labs
