On Thu, 2016-04-28 at 16:31 -0400, Luiz Capitulino wrote:
> lru_add_drain_all() works by scheduling lru_add_drain_cpu() to run
> on all CPUs that have non-empty LRU pagevecs and then waiting for
> the scheduled work to complete. However, workqueue threads may never
> have the chance to run on a CPU that's running a SCHED_FIFO task.
> This causes lru_add_drain_all() to block forever.
>
> This commit solves this problem by changing lru_add_drain_all()
> to drain the LRU pagevecs of remote CPUs. This is done by grabbing
> swapvec_lock and calling lru_add_drain_cpu().
>
> PS: This is based on an idea and initial implementation by
> Rik van Riel.
I wrote maybe half the code in this patch. It should
probably have my signed-off-by line too :)
Anyway, the patch looks fine to me and seems to work.
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
> Signed-off-by: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
> ---
> include/linux/locallock.h | 27 +++++++++++++++++++++++++++
> mm/swap.c | 35 +++++++++++++++++++++++++----------
> 2 files changed, 52 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/locallock.h b/include/linux/locallock.h
> index 6fe5928..2de478b 100644
> --- a/include/linux/locallock.h
> +++ b/include/linux/locallock.h
> @@ -104,6 +104,17 @@ static inline void __local_unlock(struct
> local_irq_lock *lv)
> put_local_var(lvar);
> \
> } while (0)
>
> +#define local_lock_other_cpu(lvar, cpu) \
> + do { \
> + __local_lock(&per_cpu(lvar, cpu)); \
> + } while (0)
> +
> +#define local_unlock_other_cpu(lvar, cpu) \
> + do { \
> + __local_unlock(&per_cpu(lvar, cpu)); \
> + } while (0)
> +
> +
> static inline void __local_lock_irq(struct local_irq_lock *lv)
> {
> spin_lock_irqsave(&lv->lock, lv->flags);
> @@ -163,6 +174,22 @@ static inline int __local_lock_irqsave(struct
> local_irq_lock *lv)
> _flags = per_cpu(lvar, cpu).flags;
> \
> } while (0)
>
> +#define local_lock_irqsave_other_cpu(lvar, _flags, cpu)
> \
> + do {
> \
> + if (cpu == smp_processor_id())
> \
> + local_lock_irqsave(lvar, _flags);
> \
> + else
> \
> + local_lock_other_cpu(lvar, cpu);
> \
> + } while (0)
> +
> +#define local_unlock_irqrestore_other_cpu(lvar, _flags, cpu)
> \
> + do {
> \
> + if (cpu == smp_processor_id())
> \
> + local_unlock_irqrestore(lvar, _flags);
> \
> + else
> \
> + local_unlock_other_cpu(lvar, cpu);
> \
> + } while (0)
> +
> static inline int __local_unlock_irqrestore(struct local_irq_lock
> *lv,
> unsigned long flags)
> {
> diff --git a/mm/swap.c b/mm/swap.c
> index ca194ae..9dc6956 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -821,9 +821,9 @@ void lru_add_drain_cpu(int cpu)
> unsigned long flags;
>
> /* No harm done if a racing interrupt already did
> this */
> - local_lock_irqsave(rotate_lock, flags);
> + local_lock_irqsave_other_cpu(rotate_lock, flags,
> cpu);
> pagevec_move_tail(pvec);
> - local_unlock_irqrestore(rotate_lock, flags);
> + local_unlock_irqrestore_other_cpu(rotate_lock,
> flags, cpu);
> }
>
> pvec = &per_cpu(lru_deactivate_file_pvecs, cpu);
> @@ -866,12 +866,32 @@ void lru_add_drain(void)
> local_unlock_cpu(swapvec_lock);
> }
>
> +static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
> +
> +#ifdef CONFIG_PREEMPT_RT_BASE
> +static inline void remote_lru_add_drain(int cpu, struct cpumask
> *has_work)
> +{
> + local_lock_other_cpu(swapvec_lock, cpu);
> + lru_add_drain_cpu(cpu);
> + local_unlock_other_cpu(swapvec_lock, cpu);
> +}
> +#else
> static void lru_add_drain_per_cpu(struct work_struct *dummy)
> {
> lru_add_drain();
> }
>
> -static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
> +static inline void remote_lru_add_drain(int cpu, struct cpumask
> *has_work)
> +{
> + struct work_struct *work =
> &per_cpu(lru_add_drain_work, cpu);
> +
> + INIT_WORK(work, lru_add_drain_per_cpu);
> + schedule_work_on(cpu, work);
> + cpumask_set_cpu(cpu, &has_work);
> +
> +}
> +#endif
> +
>
> void lru_add_drain_all(void)
> {
> @@ -884,16 +904,11 @@ void lru_add_drain_all(void)
> cpumask_clear(&has_work);
>
> for_each_online_cpu(cpu) {
> - struct work_struct *work =
> &per_cpu(lru_add_drain_work, cpu);
> -
> if (pagevec_count(&per_cpu(lru_add_pvec, cpu)) ||
> pagevec_count(&per_cpu(lru_rotate_pvecs, cpu))
> ||
> pagevec_count(&per_cpu(lru_deactivate_file_pvecs
> , cpu)) ||
> - need_activate_page_drain(cpu)) {
> - INIT_WORK(work, lru_add_drain_per_cpu);
> - schedule_work_on(cpu, work);
> - cpumask_set_cpu(cpu, &has_work);
> - }
> + need_activate_page_drain(cpu))
> + remote_lru_add_drain(cpu,
> &has_work);
> }
>
> for_each_cpu(cpu, &has_work)
--
All Rights Reversed.
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