diff options
| author | Alistair Popple <apopple@nvidia.com> | 2022-08-30 12:01:38 +1000 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2022-09-11 20:26:05 -0700 |
| commit | 0742e49026121371c7ce1f640628c68c7da175d6 (patch) | |
| tree | 7f4d5dab1a38219ff04aed245eb73a3b3eed3f0c /mm/migrate_device.c | |
| parent | 663d0cfd2e77aa3ed170df76d441c8f07efa3cf6 (diff) | |
mm/migrate_device.c: fix a misleading and outdated comment
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.
Link: https://lkml.kernel.org/r/20220830020138.497063-1-apopple@nvidia.com
Fixes: ab09243aa95a ("mm/migrate.c: remove MIGRATE_PFN_LOCKED")
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reported-by: Peter Xu <peterx@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/migrate_device.c')
| -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; |