Re: [PATCH 2/2] iommu/iova: Manage the depot list size

zhangzekun (A)
2023-08-15T14:12:30Z

在 2023/8/15 1:53, Robin Murphy 写道:
> Automatically scaling the depot up to suit the peak capacity of a
> workload is all well and good, but it would be nice to have a way to
> scale it back down again if the workload changes. To that end, add
> automatic reclaim that will gradually free unused magazines if the
> depot size remains above a reasonable threshold for long enough.
>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> drivers/iommu/iova.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index d2de6fb0e9f4..76a7d694708e 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -11,6 +11,7 @@
> #include <linux/smp.h>
> #include <linux/bitops.h>
> #include <linux/cpu.h>
> +#include <linux/workqueue.h>
>
> /* The anchor node sits above the top of the usable address space */
> #define IOVA_ANCHOR ~0UL
> @@ -626,6 +627,8 @@ EXPORT_SYMBOL_GPL(reserve_iova);
> */
> #define IOVA_MAG_SIZE 127
>
> +#define IOVA_DEPOT_DELAY msecs_to_jiffies(100)
> +
> struct iova_magazine {
> /*
> * Only full magazines are inserted into the depot, so we can avoid
> @@ -646,8 +649,11 @@ struct iova_cpu_rcache {
>
> struct iova_rcache {
> spinlock_t lock;
> + unsigned int depot_size;
> struct iova_magazine *depot;
> struct iova_cpu_rcache __percpu *cpu_rcaches;
> + struct iova_domain *iovad;
> + struct delayed_work work;
> };
>
> static struct iova_magazine *iova_magazine_alloc(gfp_t flags)
> @@ -728,6 +734,7 @@ static struct iova_magazine *iova_depot_pop(struct iova_rcache *rcache)
>
> rcache->depot = mag->next;
> mag->size = IOVA_MAG_SIZE;
> + rcache->depot_size--;
> return mag;
> }
>
> @@ -735,6 +742,24 @@ static void iova_depot_push(struct iova_rcache *rcache, struct iova_magazine *ma
> {
> mag->next = rcache->depot;
> rcache->depot = mag;
> + rcache->depot_size++;
> +}
> +
> +static void iova_depot_work_func(struct work_struct *work)
> +{
> + struct iova_rcache *rcache = container_of(work, typeof(*rcache), work.work);
> + struct iova_magazine *mag = NULL;
> +
> + spin_lock(&rcache->lock);
> + if (rcache->depot_size > num_online_cpus())
> + mag = iova_depot_pop(rcache);
> + spin_unlock(&rcache->lock);
> +
> + if (mag) {
> + iova_magazine_free_pfns(mag, rcache->iovad);
> + iova_magazine_free(mag);
> + schedule_delayed_work(&rcache->work, msecs_to_jiffies(IOVA_DEPOT_DELAY));
Hi, Robin,

I am a little confused why IOVA_DEPOT_DELAY need to be calculated twice
in iova_depot_work_func(), as it already equals to
"msecs_to_jiffies(100)". Besides, do we really need to invoke a
delayed_work in iova_depot_work_func()? As each time we put a iova
magazine to depot, a delayed_work will be invoked which is reponsible to
free a iova magazine in depot if the depot size is greater than
num_online_cpus().

Thanks,
Zekun