| Message ID | 20220830020138.497063-1-apopple@nvidia.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] mm/migrate_device.c: Fix a misleading and out-dated comment | expand |
On Tue, Aug 30, 2022 at 12:01:38PM +1000, Alistair Popple wrote: > Commit ab09243aa95a ("mm/migrate.c: remove MIGRATE_PFN_LOCKED") changed > the way trylock_page() in migrate_vma_collect_pmd() works without > updating the comment. Reword the comment to be less misleading and a > better reflection of what happens. > > Signed-off-by: Alistair Popple <apopple@nvidia.com> > Reported-by: Peter Xu <peterx@redhat.com> > Fixes: ab09243aa95a ("mm/migrate.c: remove MIGRATE_PFN_LOCKED") Acked-by: Peter Xu <peterx@redhat.com> Thanks,
diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 5052093d0262..9e7ec925ec51 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -179,9 +179,16 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, get_page(page); /* - * Optimize for the common case where page is only mapped once - * in one process. If we can lock the page, then we can safely - * set up a special migration page table entry now. + * We rely on trylock_page() to avoid deadlock between + * concurrent migrations where each is waiting on the others + * page lock. If we can't immediately lock the page we fail this + * migration as it is only best effort anyway. + * + * If we can lock the page it's safe to set up a migration entry + * now. In the common case where the page is mapped once in a + * single process setting up the migration entry now is an + * optimisation to avoid walking the rmap later with + * try_to_migrate(). */ if (trylock_page(page)) { bool anon_exclusive;
Commit ab09243aa95a ("mm/migrate.c: remove MIGRATE_PFN_LOCKED") changed the way trylock_page() in migrate_vma_collect_pmd() works without updating the comment. Reword the comment to be less misleading and a better reflection of what happens. Signed-off-by: Alistair Popple <apopple@nvidia.com> Reported-by: Peter Xu <peterx@redhat.com> Fixes: ab09243aa95a ("mm/migrate.c: remove MIGRATE_PFN_LOCKED") --- mm/migrate_device.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)