Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754805Ab2BEEZn (ORCPT ); Sat, 4 Feb 2012 23:25:43 -0500 Received: from mail-ww0-f44.google.com ([74.125.82.44]:62394 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754131Ab2BEEZl convert rfc822-to-8bit (ORCPT ); Sat, 4 Feb 2012 23:25:41 -0500 MIME-Version: 1.0 In-Reply-To: <1328271538-14502-13-git-send-email-m.szyprowski@samsung.com> References: <1328271538-14502-1-git-send-email-m.szyprowski@samsung.com> <1328271538-14502-13-git-send-email-m.szyprowski@samsung.com> Date: Sun, 5 Feb 2012 12:25:40 +0800 Message-ID: Subject: Re: [PATCH 12/15] drivers: add Contiguous Memory Allocator From: Hillf Danton To: 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, Michal Nazarewicz , Kyungmin Park , Russell King , Andrew Morton , KAMEZAWA Hiroyuki , Hillf Danton 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 Content-Length: 2880 Lines: 64 On Fri, Feb 3, 2012 at 8:18 PM, Marek Szyprowski wrote: > The Contiguous Memory Allocator is a set of helper functions for DMA > mapping framework that improves allocations of contiguous memory chunks. > > CMA grabs memory on system boot, marks it with CMA_MIGRATE_TYPE and > gives back to the system. Kernel is allowed to allocate movable pages > within CMA's managed memory so that it can be used for example for page > cache when DMA mapping do not use it. On dma_alloc_from_contiguous() > request such pages are migrated out of CMA area to free required > contiguous block and fulfill the request. This allows to allocate large > contiguous chunks of memory at any time assuming that there is enough > free memory available in the system. > > This code is heavily based on earlier works by Michal Nazarewicz. > > Signed-off-by: Marek Szyprowski > Signed-off-by: Kyungmin Park > CC: Michal Nazarewicz > Acked-by: Arnd Bergmann > Tested-by: Rob Clark > Tested-by: Ohad Ben-Cohen > Tested-by: Benjamin Gaignard > --- [...] > +/* > + * Contiguous Memory Allocator > + * > + *   The Contiguous Memory Allocator (CMA) makes it possible to > + *   allocate big contiguous chunks of memory after the system has > + *   booted. > + * > + * Why is it needed? > + * > + *   Various devices on embedded systems have no scatter-getter and/or > + *   IO map support and require contiguous blocks of memory to > + *   operate.  They include devices such as cameras, hardware video > + *   coders, etc. > + * > + *   Such devices often require big memory buffers (a full HD frame > + *   is, for instance, more then 2 mega pixels large, i.e. more than 6 > + *   MB of memory), which makes mechanisms such as kmalloc() or > + *   alloc_page() ineffective. > + * > + *   At the same time, a solution where a big memory region is > + *   reserved for a device is suboptimal since often more memory is > + *   reserved then strictly required and, moreover, the memory is > + *   inaccessible to page system even if device drivers don't use it. > + * > + *   CMA tries to solve this issue by operating on memory regions > + *   where only movable pages can be allocated from.  This way, kernel > + *   can use the memory for pagecache and when device driver requests > + *   it, allocated pages can be migrated. > + * Without boot mem reservation, what is the successful rate of CMA to serve requests of 1MiB, 2MiB, 4MiB and 8MiB chunks? -- 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/