Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755597Ab2BCJcD (ORCPT ); Fri, 3 Feb 2012 04:32:03 -0500 Received: from mailout4.w1.samsung.com ([210.118.77.14]:50732 "EHLO mailout4.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755620Ab2BCJby convert rfc822-to-8bit (ORCPT ); Fri, 3 Feb 2012 04:31:54 -0500 MIME-version: 1.0 Content-type: text/plain; charset=utf-8 Date: Fri, 03 Feb 2012 10:31:50 +0100 From: Marek Szyprowski Subject: RE: [PATCH 02/15] mm: page_alloc: update migrate type of pages on pcp when isolating In-reply-to: To: "'Michal Nazarewicz'" , "'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'" Message-id: <008101cce256$a85e29f0$f91a7dd0$%szyprowski@samsung.com> Organization: SPRC X-Mailer: Microsoft Office Outlook 12.0 Content-language: pl Content-transfer-encoding: 8BIT Thread-index: Aczh5FkRihRgMXOJQlu3qmkRbiVXZwAcW2eQ References: <1327568457-27734-1-git-send-email-m.szyprowski@samsung.com> <1327568457-27734-3-git-send-email-m.szyprowski@samsung.com> <20120130111522.GE25268@csn.ul.ie> <20120130161447.GU25268@csn.ul.ie> <022e01cce034$bc6cf440$3546dcc0$%szyprowski@samsung.com> <20120202124729.GA5796@csn.ul.ie> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3310 Lines: 79 Hello, On Thursday, February 02, 2012 8:53 PM Michał Nazarewicz wrote: > > 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. After this and some other changes I'm unable to reproduce that issue. I did a whole night tests and it still works fine, so it looks that it has been finally solved. I will post v20 patchset soon :) 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/