Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753355Ab1FOHMP (ORCPT ); Wed, 15 Jun 2011 03:12:15 -0400 Received: from mailout3.w1.samsung.com ([210.118.77.13]:57093 "EHLO mailout3.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751851Ab1FOHMO (ORCPT ); Wed, 15 Jun 2011 03:12:14 -0400 MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: text/plain; charset=utf-8 Date: Wed, 15 Jun 2011 09:11:39 +0200 From: Marek Szyprowski Subject: RE: [PATCH 08/10] mm: cma: Contiguous Memory Allocator added In-reply-to: <201106142030.07549.arnd@arndb.de> To: "'Arnd Bergmann'" , "'Michal Nazarewicz'" , Marek Szyprowski Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, linux-mm@kvack.org, linaro-mm-sig@lists.linaro.org, "'Kyungmin Park'" , "'Andrew Morton'" , "'KAMEZAWA Hiroyuki'" , "'Ankita Garg'" , "'Daniel Walker'" , "'Mel Gorman'" , "'Jesse Barker'" Message-id: <000501cc2b2b$789a54b0$69cefe10$%szyprowski@samsung.com> Organization: SPRC X-Mailer: Microsoft Office Outlook 12.0 Content-language: pl Thread-index: AcwqwTteM6782y5XQ++EZ7tOUabeiAAX3hvg References: <1307699698-29369-1-git-send-email-m.szyprowski@samsung.com> <201106141803.00876.arnd@arndb.de> <201106142030.07549.arnd@arndb.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2475 Lines: 58 Hello, On Tuesday, June 14, 2011 8:30 PM Arnd Bergmann wrote: > On Tuesday 14 June 2011 18:58:35 Michal Nazarewicz wrote: > > On Tue, 14 Jun 2011 18:03:00 +0200, Arnd Bergmann wrote: > > > For all I know, that is something that is only true for a few very > > > special Samsung devices, > > > > Maybe. I'm just answering your question. :) > > > > Ah yes, I forgot that separate regions for different purposes could > > decrease fragmentation. > > That is indeed a good point, but having a good allocator algorithm > could also solve this. I don't know too much about these allocation > algorithms, but there are probably multiple working approaches to this. > > > > I would suggest going forward without having multiple regions: > > > > Is having support for multiple regions a bad thing? Frankly, > > removing this support will change code from reading context passed > > as argument to code reading context from global variable. Nothing > > is gained; functionality is lost. > > What is bad IMHO is making them the default, which forces the board > code to care about memory management details. I would much prefer > to have contiguous allocation parameters tuned automatically to just > work on most boards before we add ways to do board-specific hacks. I see your concerns, but I really wonder how to determine the properties of the global/default cma pool. You definitely don't want to give all available memory o CMA, because it will have negative impact on kernel operation (kernel really needs to allocate unmovable pages from time to time). The only solution I see now is to provide Kconfig entry to determine the size of the global CMA pool, but this still have some issues, especially for multi-board kernels (each board probably will have different amount of RAM and different memory-consuming devices available). It looks that each board startup code still might need to tweak the size of CMA pool. I can add a kernel command line option for it, but such solution also will not solve all the cases (afair there was a discussion about kernel command line parameters for memory configuration and the conclusion was that it should be avoided). Best regards -- Marek Szyprowski Samsung Poland R&D Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/