[PATCH] nvme-core: use xarray for cel storing

[Chaitanya Kulkarni]

When using linked list we have to open code the locking, search, and
destroy operations with the loops even if data structure doesn't fall
into the fast path.

One of the main advantage of having XArray to store, search, and remove
items is that it handles all the locking by itself, avoids the loops 
when using linked lists, provides clear API to replace the linked list's
search and destroy loops. 

This patch replaces the ctrl->cel list with XArray and removes :-

a. Extra code needed for the linked list for ctrl->cel item management
   such as nvme_find_cel().
b. Destroy loop in the nvme_free_ctrl().
c. Explicit insertion locking in the nvme_get_effects_log().

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni at wdc.com>
---
 drivers/nvme/host/core.c | 31 ++++---------------------------
 drivers/nvme/host/nvme.h |  2 +-
 2 files changed, 5 insertions(+), 28 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 0d4713307724..5bf6399588a8 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3012,26 +3012,10 @@ int nvme_get_log(struct nvme_ctrl *ctrl, u32 nsid, u8 log_page, u8 lsp, u8 csi,
 	return nvme_submit_sync_cmd(ctrl->admin_q, &c, log, size);
 }
 
-static struct nvme_cel *nvme_find_cel(struct nvme_ctrl *ctrl, u8 csi)
-{
-	struct nvme_cel *cel, *ret = NULL;
-
-	spin_lock_irq(&ctrl->lock);
-	list_for_each_entry(cel, &ctrl->cels, entry) {
-		if (cel->csi == csi) {
-			ret = cel;
-			break;
-		}
-	}
-	spin_unlock_irq(&ctrl->lock);
-
-	return ret;
-}
-
 static int nvme_get_effects_log(struct nvme_ctrl *ctrl, u8 csi,
 				struct nvme_effects_log **log)
 {
-	struct nvme_cel *cel = nvme_find_cel(ctrl, csi);
+	struct nvme_cel *cel = xa_load(&ctrl->cels, csi);
 	int ret;
 
 	if (cel)
@@ -3049,10 +3033,7 @@ static int nvme_get_effects_log(struct nvme_ctrl *ctrl, u8 csi,
 	}
 
 	cel->csi = csi;
-
-	spin_lock_irq(&ctrl->lock);
-	list_add_tail(&cel->entry, &ctrl->cels);
-	spin_unlock_irq(&ctrl->lock);
+	xa_store(&ctrl->cels, cel->csi, cel, GFP_KERNEL);
 out:
 	*log = &cel->log;
 	return 0;
@@ -4431,15 +4412,11 @@ static void nvme_free_ctrl(struct device *dev)
 	struct nvme_ctrl *ctrl =
 		container_of(dev, struct nvme_ctrl, ctrl_device);
 	struct nvme_subsystem *subsys = ctrl->subsys;
-	struct nvme_cel *cel, *next;
 
 	if (!subsys || ctrl->instance != subsys->instance)
 		ida_simple_remove(&nvme_instance_ida, ctrl->instance);
 
-	list_for_each_entry_safe(cel, next, &ctrl->cels, entry) {
-		list_del(&cel->entry);
-		kfree(cel);
-	}
+	xa_destroy(&ctrl->cels);
 
 	nvme_mpath_uninit(ctrl);
 	__free_page(ctrl->discard_page);
@@ -4471,7 +4448,7 @@ int nvme_init_ctrl(struct nvme_ctrl *ctrl, struct device *dev,
 	spin_lock_init(&ctrl->lock);
 	mutex_init(&ctrl->scan_lock);
 	INIT_LIST_HEAD(&ctrl->namespaces);
-	INIT_LIST_HEAD(&ctrl->cels);
+	xa_init(&ctrl->cels);
 	init_rwsem(&ctrl->namespaces_rwsem);
 	ctrl->dev = dev;
 	ctrl->ops = ops;
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 1e6aaa710262..07bdbdc19fa0 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -300,7 +300,7 @@ struct nvme_ctrl {
 	unsigned long quirks;
 	struct nvme_id_power_state psd[32];
 	struct nvme_effects_log *effects;
-	struct list_head cels;
+	struct xarray cels;
 	struct work_struct scan_work;
 	struct work_struct async_event_work;
 	struct delayed_work ka_work;
-- 
2.22.1