Messages in this thread Patch in this message | | | From | Xu Yu <> | Subject | [PATCH] mm, thp: relax migration wait when failed to get tail page | Date | Wed, 2 Jun 2021 00:31:41 +0800 |
| |
We notice that hung task happens in a conner but practical scenario when CONFIG_PREEMPT_NONE is enabled, as follows.
Process 0 Process 1 Process 2..Inf split_huge_page_to_list unmap_page split_huge_pmd_address __migration_entry_wait(head) __migration_entry_wait(tail) remap_page (roll back) remove_migration_ptes rmap_walk_anon cond_resched
Where __migration_entry_wait(tail) is occurred in kernel space, e.g., copy_to_user, which will immediately fault again without rescheduling, and thus occupy the cpu fully.
When there are too many processes performing __migration_entry_wait on tail page, remap_page will never be done after cond_resched.
This relaxes __migration_entry_wait on tail page, thus gives remap_page a chance to complete.
Signed-off-by: Gang Deng <gavin.dg@linux.alibaba.com> Signed-off-by: Xu Yu <xuyu@linux.alibaba.com> --- mm/migrate.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c index b234c3f3acb7..df2dc39fe566 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -301,8 +301,11 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep, * is zero; but we must not call put_and_wait_on_page_locked() without * a ref. Use get_page_unless_zero(), and just fault again if it fails. */ - if (!get_page_unless_zero(page)) - goto out; + if (!get_page_unless_zero(page)) { + pte_unmap_unlock(ptep, ptl); + cond_resched(); + return; + } pte_unmap_unlock(ptep, ptl); put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE); return; -- 2.20.1.2432.ga663e714
| |