From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas =?UTF-8?B?TmllZGVycHLDvG0=?= Date: Fri, 20 Mar 2015 20:27:48 +0000 Subject: Re: [PATCH 4/8] fbdev: ssd1307fb: Use vmalloc to allocate video memory. Message-Id: <20150320212748.4bc2b42a@maestro.intranet> List-Id: 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> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable To: Geert Uytterhoeven Cc: Maxime Ripard , Tomi Valkeinen , Linux Fbdev development list , Jean-Christophe PLAGNIOL-VILLARD , "linux-kernel@vger.kernel.org" Am Fri, 20 Mar 2015 16:24:29 +0100 schrieb Geert Uytterhoeven : > 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 Niederpr=C3=BCm > >> > 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). >=20 > In that case I recommend get_zeroed_page(), to avoid the vmalloc() > overhead of setting up a mapping. I looked into get_zeroed_page() too but I thought __get_free_pages() might be more future proof since get_zeroed_page() will not reserve enough memory if more than one page is needed. This might occur if a new controller pops up that has more pixels than bits in a page or the driver is used on a system with a small page size. Also get_zeroed_page() is also just calling __get_free_pages() with the order parameter set to 0. Therefore I think a call like __get_free_pages(GFP_KERNEL | __GFP_ZERO, get_order(size))=20 does the same as get_zeroed_page() if only one page is needed but has the ability to reserve more pages if needed. Thomas From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751993AbbCTVRS (ORCPT ); Fri, 20 Mar 2015 17:17:18 -0400 Received: from mailgw1.uni-kl.de ([131.246.120.220]:58201 "EHLO mailgw1.uni-kl.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751036AbbCTVRM convert rfc822-to-8bit (ORCPT ); Fri, 20 Mar 2015 17:17:12 -0400 Date: Fri, 20 Mar 2015 21:27:48 +0100 From: Thomas =?UTF-8?B?TmllZGVycHLDvG0=?= To: Geert Uytterhoeven Cc: Maxime Ripard , Tomi Valkeinen , Linux Fbdev development list , Jean-Christophe PLAGNIOL-VILLARD , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 4/8] fbdev: ssd1307fb: Use vmalloc to allocate video memory. Message-ID: <20150320212748.4bc2b42a@maestro.intranet> In-Reply-To: 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> Organization: TU Kaiserslautern X-Mailer: Claws Mail 3.10.1 (GTK+ 2.24.26; i686-pc-linux-gnu) MIME-Version: 1.0 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 Am Fri, 20 Mar 2015 16:24:29 +0100 schrieb Geert Uytterhoeven : > 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. I looked into get_zeroed_page() too but I thought __get_free_pages() might be more future proof since get_zeroed_page() will not reserve enough memory if more than one page is needed. This might occur if a new controller pops up that has more pixels than bits in a page or the driver is used on a system with a small page size. Also get_zeroed_page() is also just calling __get_free_pages() with the order parameter set to 0. Therefore I think a call like __get_free_pages(GFP_KERNEL | __GFP_ZERO, get_order(size)) does the same as get_zeroed_page() if only one page is needed but has the ability to reserve more pages if needed. Thomas