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SubjectRe: [PATCH 4/4] mm: Do periodic rescheduling when freeing objects in kmem_free_up_q()
On Thu, Mar 21, 2019 at 05:45:12PM -0400, Waiman Long wrote:
> If the freeing queue has many objects, freeing all of them consecutively
> may cause soft lockup especially on a debug kernel. So kmem_free_up_q()
> is modified to call cond_resched() if running in the process context.
>
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> mm/slab_common.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index dba20b4208f1..633a1d0f6d20 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1622,11 +1622,14 @@ EXPORT_SYMBOL_GPL(kmem_free_q_add);
> * kmem_free_up_q - free all the objects in the freeing queue
> * @head: freeing queue head
> *
> - * Free all the objects in the freeing queue.
> + * Free all the objects in the freeing queue. The caller cannot hold any
> + * non-sleeping locks.
> */
> void kmem_free_up_q(struct kmem_free_q_head *head)
> {
> struct kmem_free_q_node *node, *next;
> + bool do_resched = !in_irq();
> + int cnt = 0;
>
> for (node = head->first; node; node = next) {
> next = node->next;
> @@ -1634,6 +1637,12 @@ void kmem_free_up_q(struct kmem_free_q_head *head)
> kmem_cache_free(node->cachep, node);
> else
> kfree(node);
> + /*
> + * Call cond_resched() every 256 objects freed when in
> + * process context.
> + */
> + if (do_resched && !(++cnt & 0xff))
> + cond_resched();

Why not just: cond_resched() ?

> }
> }
> EXPORT_SYMBOL_GPL(kmem_free_up_q);
> --
> 2.18.1
>

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