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

Robin Murphy
2023-08-14T17:54:45Z

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));
+ }
}

int iova_domain_init_rcaches(struct iova_domain *iovad)
@@ -754,6 +779,8 @@ int iova_domain_init_rcaches(struct iova_domain *iovad)

rcache = &iovad->rcaches[i];
spin_lock_init(&rcache->lock);
+ rcache->iovad = iovad;
+ INIT_DELAYED_WORK(&rcache->work, iova_depot_work_func);
rcache->cpu_rcaches = __alloc_percpu(sizeof(*cpu_rcache),
cache_line_size());
if (!rcache->cpu_rcaches) {
@@ -814,6 +841,7 @@ static bool __iova_rcache_insert(struct iova_domain *iovad,
spin_lock(&rcache->lock);
iova_depot_push(rcache, cpu_rcache->loaded);
spin_unlock(&rcache->lock);
+ schedule_delayed_work(&rcache->work, IOVA_DEPOT_DELAY);

cpu_rcache->loaded = new_mag;
can_insert = true;
@@ -915,6 +943,7 @@ static void free_iova_rcaches(struct iova_domain *iovad)
iova_magazine_free(cpu_rcache->prev);
}
free_percpu(rcache->cpu_rcaches);
+ cancel_delayed_work_sync(&rcache->work);
while ((mag = iova_depot_pop(rcache)))
iova_magazine_free(mag);
}
--
2.39.2.101.g768bb238c484.dirty