target: re-use the command S/G list for single-task commands

If we only have a single task per command (which at least in my testing
is the by far most common case) we do not have to allocate a new per-task
S/G list but can reuse the one from the command.

(nab: Fix BIDI handling in transport_free_dev_tasks)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 31 insertions, 11 deletions

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index ab4e3083d968..ac048db21240 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -3551,7 +3551,9 @@ static void transport_free_dev_tasks(struct se_cmd *cmd)
                  */
                 del_timer_sync(&task->task_timer);
 
-                kfree(task->task_sg);
+                if (task->task_sg != cmd->t_data_sg &&
+                    task->task_sg != cmd->t_bidi_data_sg)
+                        kfree(task->task_sg);
 
                 list_del(&task->t_list);
 
@@ -3830,7 +3832,33 @@ transport_allocate_data_tasks(struct se_cmd *cmd,
         lba = cmd->t_task_lba;
         sectors = DIV_ROUND_UP(cmd->data_length, sector_size);
         task_count = DIV_ROUND_UP_SECTOR_T(sectors, dev_max_sectors);
-        
+
+        /*
+         * If we need just a single task reuse the SG list in the command
+         * and avoid a lot of work.
+         */
+        if (task_count == 1) {
+                struct se_task *task;
+                unsigned long flags;
+
+                task = transport_generic_get_task(cmd, data_direction);
+                if (!task)
+                        return -ENOMEM;
+
+                task->task_sg = cmd_sg;
+                task->task_sg_nents = sgl_nents;
+
+                task->task_lba = lba;
+                task->task_sectors = sectors;
+                task->task_size = task->task_sectors * sector_size;
+
+                spin_lock_irqsave(&cmd->t_state_lock, flags);
+                list_add_tail(&task->t_list, &cmd->t_task_list);
+                spin_unlock_irqrestore(&cmd->t_state_lock, flags);
+
+                return task_count;
+        }
+
         for (i = 0; i < task_count; i++) {
                 struct se_task *task;
                 unsigned int task_size, task_sg_nents_padded;
@@ -3906,15 +3934,7 @@ transport_allocate_control_task(struct se_cmd *cmd)
         if (!task)
                 return -ENOMEM;
 
-        task->task_sg = kmalloc(sizeof(struct scatterlist) * cmd->t_data_nents,
-                                GFP_KERNEL);
-        if (!task->task_sg) {
-                cmd->se_dev->transport->free_task(task);
-                return -ENOMEM;
-        }
-
-        memcpy(task->task_sg, cmd->t_data_sg,
-               sizeof(struct scatterlist) * cmd->t_data_nents);
+        task->task_sg = cmd->t_data_sg;
         task->task_size = cmd->data_length;
         task->task_sg_nents = cmd->t_data_nents;