[PATCH 1/1] scsi: storvsc: Avoid allocating memory for temp cpumasks

[Michael Kelley <mhkelley58@gmail.com>]

Current code allocates 240 Kbytes (in typical configs) for
each synthetic SCSI controller to use as temp cpumask variables.
Recode to avoid needing the temp cpumask variables and remove the
memory allocation.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
---

This patch is for the 4.18/scsi-queue branch and improves on commit
2217a47de42f on April 20, 2018.

---
 drivers/scsi/storvsc_drv.c | 50 ++++++++++++++++++----------------------------
 1 file changed, 19 insertions(+), 31 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index d3897c4..a667119 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -474,13 +474,6 @@ struct storvsc_device {
 	 * Mask of CPUs bound to subchannels.
 	 */
 	struct cpumask alloced_cpus;
-	/*
-	 * Pre-allocated struct cpumask for each hardware queue.
-	 * struct cpumask is used by selecting out-going channels. It is a
-	 * big structure, default to 1024k bytes when CONFIG_MAXSMP=y.
-	 * Pre-allocate it to avoid allocation on the kernel stack.
-	 */
-	struct cpumask *cpumask_chns;
 	/* Used for vsc/vsp channel reset process */
 	struct storvsc_cmd_request init_request;
 	struct storvsc_cmd_request reset_request;
@@ -885,13 +878,6 @@ static int storvsc_channel_init(struct hv_device *device, bool is_fc)
 	if (stor_device->stor_chns == NULL)
 		return -ENOMEM;
 
-	stor_device->cpumask_chns = kcalloc(num_possible_cpus(),
-			sizeof(struct cpumask), GFP_KERNEL);
-	if (stor_device->cpumask_chns == NULL) {
-		kfree(stor_device->stor_chns);
-		return -ENOMEM;
-	}
-
 	stor_device->stor_chns[device->channel->target_cpu] = device->channel;
 	cpumask_set_cpu(device->channel->target_cpu,
 			&stor_device->alloced_cpus);
@@ -1252,7 +1238,6 @@ static int storvsc_dev_remove(struct hv_device *device)
 	vmbus_close(device->channel);
 
 	kfree(stor_device->stor_chns);
-	kfree(stor_device->cpumask_chns);
 	kfree(stor_device);
 	return 0;
 }
@@ -1262,7 +1247,7 @@ static struct vmbus_channel *get_og_chn(struct storvsc_device *stor_device,
 {
 	u16 slot = 0;
 	u16 hash_qnum;
-	struct cpumask *alloced_mask = &stor_device->cpumask_chns[q_num];
+	const struct cpumask *node_mask;
 	int num_channels, tgt_cpu;
 
 	if (stor_device->num_sc == 0)
@@ -1278,10 +1263,13 @@ static struct vmbus_channel *get_og_chn(struct storvsc_device *stor_device,
 	 * III. Mapping is persistent.
 	 */
 
-	cpumask_and(alloced_mask, &stor_device->alloced_cpus,
-		    cpumask_of_node(cpu_to_node(q_num)));
+	node_mask = cpumask_of_node(cpu_to_node(q_num));
 
-	num_channels = cpumask_weight(alloced_mask);
+	num_channels = 0;
+	for_each_cpu(tgt_cpu, &stor_device->alloced_cpus) {
+		if (cpumask_test_cpu(tgt_cpu, node_mask))
+			num_channels++;
+	}
 	if (num_channels == 0)
 		return stor_device->device->channel;
 
@@ -1289,7 +1277,9 @@ static struct vmbus_channel *get_og_chn(struct storvsc_device *stor_device,
 	while (hash_qnum >= num_channels)
 		hash_qnum -= num_channels;
 
-	for_each_cpu(tgt_cpu, alloced_mask) {
+	for_each_cpu(tgt_cpu, &stor_device->alloced_cpus) {
+		if (!cpumask_test_cpu(tgt_cpu, node_mask))
+			continue;
 		if (slot == hash_qnum)
 			break;
 		slot++;
@@ -1308,7 +1298,7 @@ static int storvsc_do_io(struct hv_device *device,
 	struct vstor_packet *vstor_packet;
 	struct vmbus_channel *outgoing_channel, *channel;
 	int ret = 0;
-	struct cpumask *alloced_mask;
+	const struct cpumask *node_mask;
 	int tgt_cpu;
 
 	vstor_packet = &request->vstor_packet;
@@ -1329,11 +1319,11 @@ static int storvsc_do_io(struct hv_device *device,
 			 * Ideally, we want to pick a different channel if
 			 * available on the same NUMA node.
 			 */
-			alloced_mask = &stor_device->cpumask_chns[q_num];
-			cpumask_and(alloced_mask, &stor_device->alloced_cpus,
-				    cpumask_of_node(cpu_to_node(q_num)));
-
-			for_each_cpu_wrap(tgt_cpu, alloced_mask, q_num + 1) {
+			node_mask = cpumask_of_node(cpu_to_node(q_num));
+			for_each_cpu_wrap(tgt_cpu,
+				 &stor_device->alloced_cpus, q_num + 1) {
+				if (!cpumask_test_cpu(tgt_cpu, node_mask))
+					continue;
 				if (tgt_cpu == q_num)
 					continue;
 				channel = stor_device->stor_chns[tgt_cpu];
@@ -1359,10 +1349,9 @@ static int storvsc_do_io(struct hv_device *device,
 			 * NUMA node are busy. Try to find a channel in
 			 * other NUMA nodes
 			 */
-			cpumask_andnot(alloced_mask, &stor_device->alloced_cpus,
-					cpumask_of_node(cpu_to_node(q_num)));
-
-			for_each_cpu(tgt_cpu, alloced_mask) {
+			for_each_cpu(tgt_cpu, &stor_device->alloced_cpus) {
+				if (cpumask_test_cpu(tgt_cpu, node_mask))
+					continue;
 				channel = stor_device->stor_chns[tgt_cpu];
 				if (hv_get_avail_to_write_percent(
 							&channel->outbound)
@@ -1911,7 +1900,6 @@ static int storvsc_probe(struct hv_device *device,
 
 err_out1:
 	kfree(stor_device->stor_chns);
-	kfree(stor_device->cpumask_chns);
 	kfree(stor_device);
 
 err_out0:
-- 
2.7.4