Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757016Ab2JSIgh (ORCPT ); Fri, 19 Oct 2012 04:36:37 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:56373 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1757424Ab2JSIfn (ORCPT ); Fri, 19 Oct 2012 04:35:43 -0400 X-IronPort-AV: E=Sophos;i="4.80,612,1344182400"; d="scan'208";a="6030150" Message-ID: <5081122D.1030906@cn.fujitsu.com> Date: Fri, 19 Oct 2012 16:41:17 +0800 From: Wen Congyang User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100413 Fedora/3.0.4-2.fc13 Thunderbird/3.0.4 MIME-Version: 1.0 To: KOSAKI Motohiro CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org, rientjes@google.com, liuj97@gmail.com, len.brown@intel.com, benh@kernel.crashing.org, paulus@samba.org, minchan.kim@gmail.com, akpm@linux-foundation.org, isimatu.yasuaki@jp.fujitsu.com, Christoph Lameter Subject: Re: [PATCH v3 8/9] memory-hotplug: fix NR_FREE_PAGES mismatch References: <1350629202-9664-1-git-send-email-wency@cn.fujitsu.com> <1350629202-9664-9-git-send-email-wency@cn.fujitsu.com> In-Reply-To: X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/10/19 16:35:16, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/10/19 16:35:17, Serialize complete at 2012/10/19 16:35:17 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3288 Lines: 82 At 10/19/2012 03:41 PM, KOSAKI Motohiro Wrote: > On Fri, Oct 19, 2012 at 2:46 AM, wrote: >> From: Wen Congyang >> >> NR_FREE_PAGES will be wrong after offlining pages. We add/dec NR_FREE_PAGES >> like this now: >> 1. mova all pages in buddy system to MIGRATE_ISOLATE, and dec NR_FREE_PAGES > > move? Yes. __offline_pages() start_isolate_page_range() set_migratetype_isolate() move_freepages_block() // move all pages in buddy system to MIGRATE_ISOLATE __mod_zone_freepage_state() // dec NR_FREE_PAGES > >> 2. don't add NR_FREE_PAGES when it is freed and the migratetype is MIGRATE_ISOLATE >> 3. dec NR_FREE_PAGES when offlining isolated pages. >> 4. add NR_FREE_PAGES when undoing isolate pages. >> >> When we come to step 3, all pages are in MIGRATE_ISOLATE list, and NR_FREE_PAGES >> are right. When we come to step4, all pages are not in buddy system, so we don't >> change NR_FREE_PAGES in this step, but we change NR_FREE_PAGES in step3. So >> NR_FREE_PAGES is wrong after offlining pages. So there is no need to change >> NR_FREE_PAGES in step3. > > Sorry, I don't understand this two paragraph. Can you please elaborate more? OK. If we don't online/offline memory, we add NR_FREE_PAGES when we free a page, and dec it when allocate a page. If we put the page into pcp, we don't add NR_FREE_PAGES. We will add it when the page is moved to buddy system from pcp. When we offline a memory section, we should dec NR_FREE_PAGES(we will add it when onlining memory section). The pages may be freed or inuse: 1. If the page is freed, and in buddy system. We move it to MIGRATE_ISOLATE, and dec NR_FREE_PAGES 2. If the page is inuse, we will migrate them to other memory section and free them. We don't dec NR_FREE_PAGES when it is freed because we have decreased it when it is allocated. We just put them in MIGRATE_ISOLATE. 3. If the page is in pcp, we call drain_all_pages() to put them to MIGRATE_ISOLATE. We have decreased NR_FREE_PAGES when we allocate a page and put it in pcp. So we just put them in MIGRATE_ISOLATE. Step1 deals with case1, and step2 deals with case2,3 So NR_FREE_PAGES is right after all pages are put into MIGRATE_ISOLATE list. Now offline_isolated_pages() will be called after all pages are put in MIGRATE_ISOLATE list. So we should not change NR_FREE_PAGES now, but we dec NR_FREE_PAGES in offline_isolated_pages(). > > and one more trivial question: why do we need to call > undo_isolate_page_range() from > __offline_pages()? We need to restore the page's migrate type to MIGRATE_MOVABLE. > > >> >> This patch also fixs a problem in step2: if the migratetype is MIGRATE_ISOLATE, >> we should not add NR_FRR_PAGES when we remove pages from pcppages. > > Why drain_all_pages doesn't work? > drain_all_pages() deals with case3, and it should not touch NR_FREE_PAGES if it put a page to MIGRATE_ISOLATE list. But we touch NR_FREE_PAGES without checking where the page is put. Thanks Wen Congyang -- 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/