From: Oliver Neukum <oneukum@suse.com>
To: Petr Tesarik <ptesarik@suse.com>, Oliver Neukum <oneukum@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] usb: core: warn if a GFP zone flag is passed to hcd_buffer_alloc()
Date: Wed, 16 Apr 2025 15:08:53 +0200 [thread overview]
Message-ID: <65bd42ee-ecbc-4a23-9036-42358aa086df@suse.com> (raw)
In-Reply-To: <20250416124736.3ac2bd55@mordecai>
On 16.04.25 12:47, Petr Tesarik wrote:
> If I stay with the USB buffer allocations, AFAICS the mem_flags
> parameter should be used only for non-zone flags. If you specify,
> GFP_DMA here, it will have no impact whatsoever on allocating DMA
> buffers. It may unnecessarily allocate from the DMA zone for doing PIO.
Yes. But we should not limit enforcement of such a _new_ policy
to one method in order to fix a hypothetical issue.
There is just no need for action.
> Now I think I should really write an article for LWN to debunk some
> myths about GFP_DMA.
Well, if you go to that trouble an explanation of why memflags
are passed in USB at all and how DMA works in general would be
productive.
Regards
Oliver
prev parent reply other threads:[~2025-04-16 13:08 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-20 15:47 [PATCH] usb: core: do not allocate buffers from a DMA zone unnecessarily Petr Tesarik
2025-03-25 13:40 ` [PATCH v2] usb: core: warn if a GFP zone flag is passed to hcd_buffer_alloc() Petr Tesarik
2025-03-25 13:54 ` Petr Tesarik
2025-04-09 15:40 ` Petr Tesařík
2025-04-10 6:10 ` Greg Kroah-Hartman
2025-04-11 13:57 ` Greg Kroah-Hartman
2025-04-14 7:02 ` Petr Tesarik
2025-04-14 7:12 ` Greg Kroah-Hartman
2025-04-14 7:57 ` Petr Tesarik
2025-04-15 7:53 ` Oliver Neukum
2025-04-16 7:48 ` Petr Tesarik
2025-04-16 8:45 ` Oliver Neukum
2025-04-16 10:47 ` Petr Tesarik
2025-04-16 13:08 ` Oliver Neukum [this message]
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