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b=Qz2Ew/Fo96WKMMFECtw6AcGedth0FeblIay9/D+sibhjAK2/BTaqye6hTBWLs8zRw qXakXIrkxjuU89HS4vq0KEDl4x5Z+5neqSP1lPuX0OLciuKdgyqjd9FTsSHKpkKbON +rEI4WgECsqIzEjtNQqxUwhobsANlSwbLo0+gejc7TXvcdF2esdVnYMH+viUhY4Vxs I5YPwI+B873UPnl851liAilmTnKwoRgKEBL/Qkp67CXcRlVxi7w0cHqyTfePTjs2ij SqS2cmlvhnjlis8DLSAigHIQ3woqHE6gL5snkeJGrQ1zoiv/+OdHptqVqSk/XgvaGn Hno8waIJ7Q4NA== Message-ID: Date: Wed, 2 Sep 2026 16:36:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] USB: usbfs: replace __get_free_page() with kmalloc() Content-Language: en-US To: Alan Stern , Oliver Neukum Cc: "Mike Rapoport (Microsoft)" , Chas Williams <3chas3@gmail.com>, Duncan Sands , Greg Kroah-Hartman , Johan Hovold , Andrew Morton , David Hildenbrand , Matthew Wilcox , accessrunner-general@lists.sourceforge.net, linux-atm-general@lists.sourceforge.net, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-usb@vger.kernel.org, netdev@vger.kernel.org References: <20260830-usb-v1-0-aa349c302246@kernel.org> <20260830-usb-v1-1-aa349c302246@kernel.org> <8cbe558e-7f53-4ce4-be8e-52fdba9105d4@rowland.harvard.edu> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: w64tqfcjpipstgiskf757mdq5udt58zu X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E99A616000F X-Rspam-User: X-HE-Tag: 1788359771-516503 X-HE-Meta: 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 MhbrBHmQ w0OVllBJOhqEijfw8IC9A456nG53KIt/gRUfULLmeS7iWk1hAnoLKf8hjAfHyYSY2PvffDfVFQF5Ci5JNzqQBBOXpZ3GNBSPCNtWzFIKTzlNOnWGXdqgdyqK7Niwr0E5A0A9gkKC0fyYg8KoJO8c7t0a84zA0GPHMKa8fzyDYqrspm6X6F5bqQdHL4KmtBGhq3yTCotlPDIeRxsAQsqZIX3/qGntBeSIDmtHLNdSfSymHaDBsFx8/Oe3eJHe0DlCBBBY/2n8PPb+Eh4ReLiSn5kU7qAW2JgNzz+Uj8XfJ2B5xJApBFbiII7gCTw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/31/26 16:30, Alan Stern wrote: > On Mon, Aug 31, 2026 at 03:27:07PM +0200, Oliver Neukum wrote: >> On 30.08.26 10:10, Mike Rapoport (Microsoft) wrote: >> > do_proc_control() allocates a temporary buffer for the data stage of a >> > control transfer issued from userspace. >> > >> > This buffer can be allocated with kmalloc() as there's nothing special >> > about it to go directly to the page allocator. >> >> You are breaking the calculation. A page has a size of exactly >> PAGE_SIZE. A kmalloced object of PAGE_SIZE is larger. That is >> a bad idea. > > By "the calculation", are you referring to the > usbfs_increase_memory_usage() call in do_proc_control()? > > The overhead in kmalloc allocations doesn't really matter for this > purpose -- it can be considered a rounding error. FWIW, the overhead will be zero for a PAGE_SIZE size, unless slab debugging is enabled, but you can ignore it. > Besides, we don't > know how big the overhead is, so we can't account for it. You can see > that in the same call, we don't try to account for the overhead involved > in usb_alloc_urb() or kmalloc_obj() either. ksize() exists but I wouldn't bother indeed. > I'd say there's nothing wrong with this patch. Agreed. > Alan Stern