linux-kernel - [PATCH] iommu/iova: use named kmem

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Message-ID: <20240201193014.2785570-1-tatashin@google.com>
Date: Thu,  1 Feb 2024 19:30:14 +0000
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: robin.murphy@....com,
	joro@...tes.org,
	will@...nel.org,
	iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	pasha.tatashin@...een.com,
	rientjes@...gle.com
Subject: [PATCH] iommu/iova: use named kmem_cache for iova magazines

From: Pasha Tatashin <pasha.tatashin@...een.com>

The magazine buffers can take gigabytes of kmem memory, dominating all
other allocations. For observability prurpose create named slab cache so
the iova magazine memory overhead can be clearly observed.

With this change:

> slabtop -o | head
 Active / Total Objects (% used)    : 869731 / 952904 (91.3%)
 Active / Total Slabs (% used)      : 103411 / 103974 (99.5%)
 Active / Total Caches (% used)     : 135 / 211 (64.0%)
 Active / Total Size (% used)       : 395389.68K / 411430.20K (96.1%)
 Minimum / Average / Maximum Object : 0.02K / 0.43K / 8.00K

OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
244412 244239 99%    1.00K  61103       4    244412K iommu_iova_magazine
 91636  88343 96%    0.03K    739     124      2956K kmalloc-32
 75744  74844 98%    0.12K   2367      32      9468K kernfs_node_cache

On this machine it is now clear that magazine use 242M of kmem memory.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 drivers/iommu/iova.c | 57 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 54 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index d30e453d0fb4..617bbc2b79f5 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -630,6 +630,10 @@ EXPORT_SYMBOL_GPL(reserve_iova);
 
 #define IOVA_DEPOT_DELAY msecs_to_jiffies(100)
 
+static struct kmem_cache *iova_magazine_cache;
+static unsigned int iova_magazine_cache_users;
+static DEFINE_MUTEX(iova_magazine_cache_mutex);
+
 struct iova_magazine {
 	union {
 		unsigned long size;
@@ -654,11 +658,51 @@ struct iova_rcache {
 	struct delayed_work work;
 };
 
+static int iova_magazine_cache_init(void)
+{
+	int ret = 0;
+
+	mutex_lock(&iova_magazine_cache_mutex);
+
+	iova_magazine_cache_users++;
+	if (iova_magazine_cache_users > 1)
+		goto out_unlock;
+
+	iova_magazine_cache = kmem_cache_create("iommu_iova_magazine",
+						sizeof(struct iova_magazine),
+						0, SLAB_HWCACHE_ALIGN, NULL);
+
+	if (!iova_magazine_cache) {
+		pr_err("Couldn't create iova magazine cache\n");
+		ret = -ENOMEM;
+	}
+
+out_unlock:
+	mutex_unlock(&iova_magazine_cache_mutex);
+
+	return ret;
+}
+
+static void iova_magazine_cache_fini(void)
+{
+	mutex_lock(&iova_magazine_cache_mutex);
+
+	if (WARN_ON(!iova_magazine_cache_users))
+		goto out_unlock;
+
+	iova_magazine_cache_users--;
+	if (!iova_magazine_cache_users)
+		kmem_cache_destroy(iova_magazine_cache);
+
+out_unlock:
+	mutex_unlock(&iova_magazine_cache_mutex);
+}
+
 static struct iova_magazine *iova_magazine_alloc(gfp_t flags)
 {
 	struct iova_magazine *mag;
 
-	mag = kmalloc(sizeof(*mag), flags);
+	mag = kmem_cache_alloc(iova_magazine_cache, flags);
 	if (mag)
 		mag->size = 0;
 
@@ -667,7 +711,7 @@ static struct iova_magazine *iova_magazine_alloc(gfp_t flags)
 
 static void iova_magazine_free(struct iova_magazine *mag)
 {
-	kfree(mag);
+	kmem_cache_free(iova_magazine_cache, mag);
 }
 
 static void
@@ -766,11 +810,17 @@ int iova_domain_init_rcaches(struct iova_domain *iovad)
 	unsigned int cpu;
 	int i, ret;
 
+	ret = iova_magazine_cache_init();
+	if (ret)
+		return -ENOMEM;
+
 	iovad->rcaches = kcalloc(IOVA_RANGE_CACHE_MAX_SIZE,
 				 sizeof(struct iova_rcache),
 				 GFP_KERNEL);
-	if (!iovad->rcaches)
+	if (!iovad->rcaches) {
+		iova_magazine_cache_fini();
 		return -ENOMEM;
+	}
 
 	for (i = 0; i < IOVA_RANGE_CACHE_MAX_SIZE; ++i) {
 		struct iova_cpu_rcache *cpu_rcache;
@@ -948,6 +998,7 @@ static void free_iova_rcaches(struct iova_domain *iovad)
 
 	kfree(iovad->rcaches);
 	iovad->rcaches = NULL;
+	iova_magazine_cache_fini();
 }
 
 /*
-- 
2.43.0.594.gd9cf4e227d-goog