From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx203.postini.com [74.125.245.203]) by kanga.kvack.org (Postfix) with SMTP id 8AB086B002C for ; Thu, 2 Feb 2012 14:53:30 -0500 (EST) Received: by eaag11 with SMTP id g11so1331801eaa.14 for ; Thu, 02 Feb 2012 11:53:28 -0800 (PST) Content-Type: text/plain; charset=utf-8; format=flowed; delsp=yes 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: Quoted-Printable From: "Michal Nazarewicz" Message-ID: In-Reply-To: <20120202124729.GA5796@csn.ul.ie> Sender: owner-linux-mm@kvack.org List-ID: 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' > 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_MO= VABLE. 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 p= age 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 it= s pageblock's migrate type is MIGRATE_ISOLATE. When allocation happens and pcp list is empty, rmqueue_bulk() will get e= xecuted with migratetype argument set to MIGRATE_MOVABLE. It calls __rmqueue() = to grab some pages and because the page described above is on MIGRATE_CMA freeli= st 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 b= ack on MIGRATE_MOVABLE pcp list but this time with page_private =3D=3D MIGRA= TE_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_co= ld_page() will do the right thing by reading pageblock's migrate type. Marek is currently experimenting with various patches including the foll= owing change: #ifdef CONFIG_CMA int mt =3D get_pageblock_migratetype(page); if (is_migrate_cma(mt) || mt =3D=3D 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 o= f the freelist it took page from, we could avoid this get_pageblock_migratetyp= e() 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' \,=3D./ `o ..o | Computer Science, Micha=C5=82 =E2=80=9Cmina86=E2=80=9D Nazarewicz= (o o) ooo +------------------ooO--(_)--Ooo-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org