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([2001:a61:1350:fd01:ac0d:cf4f:2906:b446]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39eaf43cd17sm17165723f8f.78.2025.04.16.06.08.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Apr 2025 06:08:56 -0700 (PDT) Message-ID: <65bd42ee-ecbc-4a23-9036-42358aa086df@suse.com> Date: Wed, 16 Apr 2025 15:08:53 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] usb: core: warn if a GFP zone flag is passed to hcd_buffer_alloc() To: Petr Tesarik , Oliver Neukum Cc: Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250320154733.392410-1-ptesarik@suse.com> <20250325134000.575794-1-ptesarik@suse.com> <2025041110-starch-abroad-5311@gregkh> <20250414090216.596ebd11@mordecai> <522b3049-8e7f-41d4-a811-3385992a4d46@suse.com> <20250416094807.2545efd8@mordecai> <20250416124736.3ac2bd55@mordecai> Content-Language: en-US From: Oliver Neukum In-Reply-To: <20250416124736.3ac2bd55@mordecai> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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