From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 177F04A2E3C; Wed, 2 Sep 2026 14:36:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788359772; cv=none; b=AJpQ/cAq3x7jLz8X/YqzdycQbrW+57rN+g0gFasOrWddAV2Qan/caX56h9ZarEYlzLMeimJploQLeqrEvzWtJZCfm3shsRCjxhSQNSIoC1NBhoB6mWmcbpEFPtBQ0IeC0txZ8ZFRUjsiBXuXbqtzhRKBH3MEqG0sTSDtBL1VilE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788359772; c=relaxed/simple; bh=eJC9UUBWutn2N8t4IKPJkVXhNrPPSiqt3WTyCAhkfEE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Z8l0+bG+l1s0O61sRairy2MqdktKzqxHcHfEuEYqufX/8ir7/mYcSxLtvBE6C/yMvoWpYncNyVwFDNWp5b4oyHcQRib/CamuxDtgJC5wsf/7qbWU04ITUpCDTiB+4bgVpo8+2q/6bH/DG0p1TmV8IikLzDTLF3uXgH2eRdnhP8g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Qz2Ew/Fo; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Qz2Ew/Fo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B1DAE1F000E9; Wed, 2 Sep 2026 14:36:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788359770; bh=uzzpWL0xLJV4HxgXaJDCRpeFEK+cpnvsfs6kVzVfAak=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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