diff options
| -rw-r--r-- | mm/migrate_device.c | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 27fb37d65476..72354248dde9 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -185,9 +185,16 @@ again: 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; |