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>

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index ab4e3083d9684a6bbbd148fe210c31fc627151dc..ac048db212406842c96a907f2bd7530d89f8ab64 100644 (file)
--- 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;