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

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Message-ID: <48d5cae9-ff7c-4076-8b71-8c16bcf00443@suse.com>
Date: Tue, 13 May 2025 10:11:20 +0200
From: Oliver Neukum <oneukum@...e.com>
To: David Wang <00107082@....com>, mathias.nyman@...el.com,
 gregkh@...uxfoundation.org
Cc: stern@...land.harvard.edu, surenb@...gle.com, kent.overstreet@...ux.dev,
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] USB: core: add a memory pool to urb for
 host-controller private data

Hi,

On 13.05.25 07:54, David Wang wrote:
> 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.

First of all, thank you for trying to tackle this long running issue.

> @@ -77,6 +78,7 @@ struct urb *usb_alloc_urb(int iso_packets, gfp_t mem_flags)
>   	if (!urb)
>   		return NULL;
>   	usb_init_urb(urb);
> +	urb->hcpriv_mempool_flags = mem_flags;

No. You cannot do this. The flags you pass to usb_alloc_urb()
depend on the context you call it in. For example, if you are
allocating it while holding a spinlock, ou need to use GFP_ATOMIC

But that may or may not be the same context you submit the URB in.
Recording mem_flags here makes no sense.

	Regards
		Oliver