linux-kernel - [PATCH v2 1/2] USB: core: add a memory pool to urb for host-controller private data

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Message-Id: <20250513113817.11962-1-00107082@163.com>
Date: Tue, 13 May 2025 19:38:17 +0800
From: David Wang <00107082@....com>
To: mathias.nyman@...el.com,
	gregkh@...uxfoundation.org,
	oneukum@...e.com
Cc: stern@...land.harvard.edu,
	linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	David Wang <00107082@....com>
Subject: [PATCH v2 1/2] USB: core: add a memory pool to urb for host-controller private data

---
Changes:
1. Use caller's mem_flags if a larger memory is needed.
Thanks to Oliver Neukum <oneukum@...e.com>'s review.
---
URB objects have long lifecycle, an urb can be reused between
enqueue-dequeue loops; The private data needed by some host controller
has very short lifecycle, the memory is alloced when enqueue, and
released when dequeue. For example, on a system with xhci, several
minutes of usage of webcam/keyboard/mouse have memory alloc counts:
  drivers/usb/core/urb.c:75 [usbcore] func:usb_alloc_urb 661
  drivers/usb/host/xhci.c:1555 [xhci_hcd] func:xhci_urb_enqueue 424863
Memory allocation frequency for host-controller private data can reach
~1k/s and above.

High frequent allocations for host-controller private data can be
avoided if urb take over the ownership of memory, the memory then shares
the longer lifecycle with urb objects.

Add a mempool to urb for hcpriv usage, the mempool only holds one block
of memory and grows when larger size is requested.

Signed-off-by: David Wang <00107082@....com>
---
 drivers/usb/core/urb.c | 23 +++++++++++++++++++++++
 include/linux/usb.h    |  3 +++
 2 files changed, 26 insertions(+)

diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
index 5e52a35486af..51bf25125aeb 100644
--- a/drivers/usb/core/urb.c
+++ b/drivers/usb/core/urb.c
@@ -23,6 +23,7 @@ static void urb_destroy(struct kref *kref)
 
 	if (urb->transfer_flags & URB_FREE_BUFFER)
 		kfree(urb->transfer_buffer);
+	kfree(urb->hcpriv_mempool);
 
 	kfree(urb);
 }
@@ -1037,3 +1038,25 @@ int usb_anchor_empty(struct usb_anchor *anchor)
 
 EXPORT_SYMBOL_GPL(usb_anchor_empty);
 
+/**
+ * urb_hcpriv_mempool_zalloc - alloc memory from mempool for hcpriv
+ * @urb: pointer to URB being used
+ * @size: memory size requested by current host controller
+ * @mem_flags: the type of memory to allocate
+ *
+ * Return: NULL if out of memory, otherwise memory are zeroed
+ */
+void *urb_hcpriv_mempool_zalloc(struct urb *urb, size_t size, gfp_t mem_flags)
+{
+	if (urb->hcpriv_mempool_size < size) {
+		kfree(urb->hcpriv_mempool);
+		urb->hcpriv_mempool_size = size;
+		urb->hcpriv_mempool = kmalloc(size, mem_flags);
+	}
+	if (urb->hcpriv_mempool)
+		memset(urb->hcpriv_mempool, 0, size);
+	else
+		urb->hcpriv_mempool_size = 0;
+	return urb->hcpriv_mempool;
+}
+EXPORT_SYMBOL_GPL(urb_hcpriv_mempool_zalloc);
diff --git a/include/linux/usb.h b/include/linux/usb.h
index b46738701f8d..4400e41271bc 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1602,6 +1602,8 @@ struct urb {
 	struct kref kref;		/* reference count of the URB */
 	int unlinked;			/* unlink error code */
 	void *hcpriv;			/* private data for host controller */
+	void *hcpriv_mempool;           /* a single slot of cache for HCD's private data */
+	size_t hcpriv_mempool_size;     /* current size of the memory pool */
 	atomic_t use_count;		/* concurrent submissions counter */
 	atomic_t reject;		/* submissions will fail */
 
@@ -1790,6 +1792,7 @@ extern int usb_wait_anchor_empty_timeout(struct usb_anchor *anchor,
 extern struct urb *usb_get_from_anchor(struct usb_anchor *anchor);
 extern void usb_scuttle_anchored_urbs(struct usb_anchor *anchor);
 extern int usb_anchor_empty(struct usb_anchor *anchor);
+extern void *urb_hcpriv_mempool_zalloc(struct urb *urb, size_t size, gfp_t mem_flags);
 
 #define usb_unblock_urb	usb_unpoison_urb
 
-- 
2.39.2