[SCSI] add support for per-host cmd pools

This allows drivers to specify the size of their per-command private
data in the host template and then get extra memory allocated for
each command instead of needing another allocation in ->queuecommand.

With the current SCSI code that already does multiple allocations for
each command this probably doesn't make a big performance impact, but
it allows to clean up the drivers, and prepare them for using the
blk-mq infrastructure where the common allocation will make a difference.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/scsi.c

@@ -331,46 +331,103 @@ void scsi_put_command(struct scsi_cmnd *cmd)
 }
 EXPORT_SYMBOL(scsi_put_command);
 
-static struct scsi_host_cmd_pool *scsi_get_host_cmd_pool(gfp_t gfp_mask)
+static struct scsi_host_cmd_pool *
+scsi_find_host_cmd_pool(struct Scsi_Host *shost)
 {
+	if (shost->hostt->cmd_size)
+		return shost->hostt->cmd_pool;
+	if (shost->unchecked_isa_dma)
+		return &scsi_cmd_dma_pool;
+	return &scsi_cmd_pool;
+}
+
+static void
+scsi_free_host_cmd_pool(struct scsi_host_cmd_pool *pool)
+{
+	kfree(pool->sense_name);
+	kfree(pool->cmd_name);
+	kfree(pool);
+}
+
+static struct scsi_host_cmd_pool *
+scsi_alloc_host_cmd_pool(struct Scsi_Host *shost)
+{
+	struct scsi_host_template *hostt = shost->hostt;
+	struct scsi_host_cmd_pool *pool;
+
+	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
+	if (!pool)
+		return NULL;
+
+	pool->cmd_name = kasprintf(GFP_KERNEL, "%s_cmd", hostt->name);
+	pool->sense_name = kasprintf(GFP_KERNEL, "%s_sense", hostt->name);
+	if (!pool->cmd_name || !pool->sense_name) {
+		scsi_free_host_cmd_pool(pool);
+		return NULL;
+	}
+
+	pool->slab_flags = SLAB_HWCACHE_ALIGN;
+	if (shost->unchecked_isa_dma) {
+		pool->slab_flags |= SLAB_CACHE_DMA;
+		pool->gfp_mask = __GFP_DMA;
+	}
+	return pool;
+}
+
+static struct scsi_host_cmd_pool *
+scsi_get_host_cmd_pool(struct Scsi_Host *shost)
+{
+	struct scsi_host_template *hostt = shost->hostt;
 	struct scsi_host_cmd_pool *retval = NULL, *pool;
+	size_t cmd_size = sizeof(struct scsi_cmnd) + hostt->cmd_size;
+
 	/*
 	 * Select a command slab for this host and create it if not
 	 * yet existent.
 	 */
 	mutex_lock(&host_cmd_pool_mutex);
-	pool = (gfp_mask & __GFP_DMA) ? &scsi_cmd_dma_pool :
-		&scsi_cmd_pool;
+	pool = scsi_find_host_cmd_pool(shost);
+	if (!pool) {
+		pool = scsi_alloc_host_cmd_pool(shost);
+		if (!pool)
+			goto out;
+	}
+
 	if (!pool->users) {
-		pool->cmd_slab = kmem_cache_create(pool->cmd_name,
-						   sizeof(struct scsi_cmnd), 0,
+		pool->cmd_slab = kmem_cache_create(pool->cmd_name, cmd_size, 0,
 						   pool->slab_flags, NULL);
 		if (!pool->cmd_slab)
-			goto fail;
+			goto out_free_pool;
 
 		pool->sense_slab = kmem_cache_create(pool->sense_name,
 						     SCSI_SENSE_BUFFERSIZE, 0,
 						     pool->slab_flags, NULL);
-		if (!pool->sense_slab) {
-			kmem_cache_destroy(pool->cmd_slab);
-			goto fail;
-		}
+		if (!pool->sense_slab)
+			goto out_free_slab;
 	}
 
 	pool->users++;
 	retval = pool;
- fail:
+out:
 	mutex_unlock(&host_cmd_pool_mutex);
 	return retval;
+
+out_free_slab:
+	kmem_cache_destroy(pool->cmd_slab);
+out_free_pool:
+	if (hostt->cmd_size)
+		scsi_free_host_cmd_pool(pool);
+	goto out;
 }
 
-static void scsi_put_host_cmd_pool(gfp_t gfp_mask)
+static void scsi_put_host_cmd_pool(struct Scsi_Host *shost)
 {
+	struct scsi_host_template *hostt = shost->hostt;
 	struct scsi_host_cmd_pool *pool;
 
 	mutex_lock(&host_cmd_pool_mutex);
-	pool = (gfp_mask & __GFP_DMA) ? &scsi_cmd_dma_pool :
-		&scsi_cmd_pool;
+	pool = scsi_find_host_cmd_pool(shost);
+
 	/*
 	 * This may happen if a driver has a mismatched get and put
 	 * of the command pool; the driver should be implicated in
@@ -381,6 +438,8 @@ static void scsi_put_host_cmd_pool(gfp_t gfp_mask)
 	if (!--pool->users) {
 		kmem_cache_destroy(pool->cmd_slab);
 		kmem_cache_destroy(pool->sense_slab);
+		if (hostt->cmd_size)
+			scsi_free_host_cmd_pool(pool);
 	}
 	mutex_unlock(&host_cmd_pool_mutex);
 }
@@ -397,14 +456,13 @@ static void scsi_put_host_cmd_pool(gfp_t gfp_mask)
  */
 int scsi_setup_command_freelist(struct Scsi_Host *shost)
 {
-	struct scsi_cmnd *cmd;
 	const gfp_t gfp_mask = shost->unchecked_isa_dma ? GFP_DMA : GFP_KERNEL;
+	struct scsi_cmnd *cmd;
 
 	spin_lock_init(&shost->free_list_lock);
 	INIT_LIST_HEAD(&shost->free_list);
 
-	shost->cmd_pool = scsi_get_host_cmd_pool(gfp_mask);
-
+	shost->cmd_pool = scsi_get_host_cmd_pool(shost);
 	if (!shost->cmd_pool)
 		return -ENOMEM;
 
@@ -413,7 +471,7 @@ int scsi_setup_command_freelist(struct Scsi_Host *shost)
 	 */
 	cmd = scsi_host_alloc_command(shost, gfp_mask);
 	if (!cmd) {
-		scsi_put_host_cmd_pool(gfp_mask);
+		scsi_put_host_cmd_pool(shost);
 		shost->cmd_pool = NULL;
 		return -ENOMEM;
 	}
@@ -442,7 +500,7 @@ void scsi_destroy_command_freelist(struct Scsi_Host *shost)
 		scsi_host_free_command(shost, cmd);
 	}
 	shost->cmd_pool = NULL;
-	scsi_put_host_cmd_pool(shost->unchecked_isa_dma ? GFP_DMA : GFP_KERNEL);
+	scsi_put_host_cmd_pool(shost);
 }
 
 #ifdef CONFIG_SCSI_LOGGING

include/scsi/scsi_host.h

@@ -15,6 +15,7 @@ struct completion;
 struct module;
 struct scsi_cmnd;
 struct scsi_device;
+struct scsi_host_cmd_pool;
 struct scsi_target;
 struct Scsi_Host;
 struct scsi_host_cmd_pool;
@@ -524,6 +525,12 @@ struct scsi_host_template {
 	 *   scsi_netlink.h
 	 */
 	u64 vendor_id;
+
+	/*
+	 * Additional per-command data allocated for the driver.
+	 */
+	unsigned int cmd_size;
+	struct scsi_host_cmd_pool *cmd_pool;
 };
 
 /*