From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752498AbbCTPY4 (ORCPT ); Fri, 20 Mar 2015 11:24:56 -0400 Received: from mail-oi0-f53.google.com ([209.85.218.53]:33381 "EHLO mail-oi0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751962AbbCTPYa convert rfc822-to-8bit (ORCPT ); Fri, 20 Mar 2015 11:24:30 -0400 MIME-Version: 1.0 In-Reply-To: <20150320144740.GH4255@lukather> References: <1423261694-5939-1-git-send-email-niederp@physik.uni-kl.de> <1423261694-5939-5-git-send-email-niederp@physik.uni-kl.de> <20150207111821.GN2079@lukather> <20150207163541.30047a33@maestro.intranet> <20150212151121.GJ2079@lukather> <20150214152212.1643da7d@maestro.intranet> <54FED559.2030506@ti.com> <20150313223128.2a3a682e@maestro.intranet> <550C068E.1070305@ti.com> <20150320144740.GH4255@lukather> Date: Fri, 20 Mar 2015 16:24:29 +0100 X-Google-Sender-Auth: mv_7Rha6JZBVIuZO-wx-kmyjN24 Message-ID: Subject: Re: [PATCH 4/8] fbdev: ssd1307fb: Use vmalloc to allocate video memory. From: Geert Uytterhoeven To: Maxime Ripard Cc: Tomi Valkeinen , =?UTF-8?Q?Thomas_Niederpr=C3=BCm?= , Linux Fbdev development list , Jean-Christophe PLAGNIOL-VILLARD , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 20, 2015 at 3:47 PM, Maxime Ripard wrote: > On Fri, Mar 20, 2015 at 01:37:50PM +0200, Tomi Valkeinen wrote: >> On 15/03/15 00:02, Geert Uytterhoeven wrote: >> > On Fri, Mar 13, 2015 at 10:31 PM, Thomas Niederprüm >> > wrote: >> >> Am Tue, 10 Mar 2015 13:28:25 +0200 >> >> schrieb Tomi Valkeinen : >> >>> Also, isn't doing __pa() for the memory returned by vmalloc plain >> >>> wrong? >> >> >> >>> What was the crash about when using kmalloc? It would be good to fix >> >>> defio, as I don't see why it should not work with kmalloced memory. >> >> >> >> The main challenge here is that the memory handed to userspace upon >> >> mmap call needs to be page aligned. The memory returned by kmalloc has >> >> no such alignment, but the pointer presented to the userspace program >> >> gets aligned to next page boundary. It's not clear to me whether there >> >> is an easy way to obtain page aligned kmalloc memory. Memory >> >> allocated by vmalloc on the other hand is always aligned to page >> >> boundaries. This is why I chose to go for vmalloc. >> > >> > __get_free_pages()? >> >> I'm not that experienced with mem management, so I have to ask... >> __get_free_pages() probably works fine, but isn't vmalloc better here? >> >> __get_free_pages() will give you possibly a lot more memory than you >> need. And the memory is contiguous, so it could be difficult to allocate >> a larger memory area. The driver doesn't need contiguous memory (except >> in the virtual sense). > > vmalloc also returns pages, so the size will be page-aligned. It > doesn't make much of a difference here, since we will only use a > single page in both case (the max resolution of these screens is > 128x39, with one bit per pixel). In that case I recommend get_zeroed_page(), to avoid the vmalloc() overhead of setting up a mapping. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds