Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933487Ab2BBTxc (ORCPT ); Thu, 2 Feb 2012 14:53:32 -0500 Received: from mail-ey0-f174.google.com ([209.85.215.174]:61503 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933313Ab2BBTxa convert rfc822-to-8bit (ORCPT ); Thu, 2 Feb 2012 14:53:30 -0500 Content-Type: text/plain; charset=utf-8; format=flowed; delsp=yes To: "Marek Szyprowski" , "Mel Gorman" 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'" , "'Russell King'" , "'Andrew Morton'" , "'KAMEZAWA Hiroyuki'" , "'Daniel Walker'" , "'Arnd Bergmann'" , "'Jesse Barker'" , "'Jonathan Corbet'" , "'Shariq Hasnain'" , "'Chunsang Jeong'" , "'Dave Hansen'" , "'Benjamin Gaignard'" Subject: Re: [PATCH 02/15] mm: page_alloc: update migrate type of pages on pcp when isolating References: <1327568457-27734-1-git-send-email-m.szyprowski@samsung.com> <1327568457-27734-3-git-send-email-m.szyprowski@samsung.com> <20120130111522.GE25268@csn.ul.ie> <20120130161447.GU25268@csn.ul.ie> <022e01cce034$bc6cf440$3546dcc0$%szyprowski@samsung.com> <20120202124729.GA5796@csn.ul.ie> Date: Thu, 02 Feb 2012 20:53:25 +0100 MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT From: "Michal Nazarewicz" Message-ID: In-Reply-To: <20120202124729.GA5796@csn.ul.ie> User-Agent: Opera Mail/11.61 (Linux) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3119 Lines: 70 > On Tue, Jan 31, 2012 at 05:23:59PM +0100, Marek Szyprowski wrote: >> Pages, which have incorrect migrate type on free finally >> causes pageblock migration type change from MIGRATE_CMA to MIGRATE_MOVABLE. On Thu, 02 Feb 2012 13:47:29 +0100, Mel Gorman wrote: > I'm not quite seeing this. In free_hot_cold_page(), the pageblock > type is checked so the page private should be set to MIGRATE_CMA or > MIGRATE_ISOLATE for the CMA area. It's not clear how this can change a > pageblock to MIGRATE_MOVABLE in error. Here's what I think may happen: When drain_all_pages() is called, __free_one_page() is called for each page on pcp list with migrate type deducted from page_private() which is MIGRATE_CMA. This result in the page being put on MIGRATE_CMA freelist even though its pageblock's migrate type is MIGRATE_ISOLATE. When allocation happens and pcp list is empty, rmqueue_bulk() will get executed with migratetype argument set to MIGRATE_MOVABLE. It calls __rmqueue() to grab some pages and because the page described above is on MIGRATE_CMA freelist it may be returned back to rmqueue_bulk(). But, pageblock's migrate type is not MIGRATE_CMA but MIGRATE_ISOLATE, so the following code: #ifdef CONFIG_CMA if (is_pageblock_cma(page)) set_page_private(page, MIGRATE_CMA); else #endif set_page_private(page, migratetype); will set it's private to MIGRATE_MOVABLE and in the end the page lands back on MIGRATE_MOVABLE pcp list but this time with page_private == MIGRATE_MOVABLE and not MIGRATE_CMA. One more drain_all_pages() (which may happen since alloc_contig_range() calls set_migratetype_isolate() for each block) and next __rmqueue_fallback() may convert the whole pageblock to MIGRATE_MOVABLE. I know, this sounds crazy and improbable, but I couldn't find an easier path to destruction. As you pointed, once the page is allocated, free_hot_cold_page() will do the right thing by reading pageblock's migrate type. Marek is currently experimenting with various patches including the following change: #ifdef CONFIG_CMA int mt = get_pageblock_migratetype(page); if (is_migrate_cma(mt) || mt == MIGRATE_ISOLATE) set_page_private(page, mt); else #endif set_page_private(page, migratetype); As a matter of fact, if __rmqueue() was changed to return migrate type of the freelist it took page from, we could avoid this get_pageblock_migratetype() all together. For now, however, I'd rather not go that way just yet -- I'll be happy to dig into it once CMA gets merged. -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Michał “mina86” Nazarewicz (o o) ooo +------------------ooO--(_)--Ooo-- -- 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/