Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753843Ab2FUEzL (ORCPT ); Thu, 21 Jun 2012 00:55:11 -0400 Received: from LGEMRELSE1Q.lge.com ([156.147.1.111]:43848 "EHLO LGEMRELSE1Q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753517Ab2FUEzJ (ORCPT ); Thu, 21 Jun 2012 00:55:09 -0400 X-AuditID: 9c93016f-b7cbdae0000024ac-b8-4fe2a92b4836 Message-ID: <4FE2A937.6040701@kernel.org> Date: Thu, 21 Jun 2012 13:55:19 +0900 From: Minchan Kim User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 Newsgroups: gmane.linux.kernel.mm,gmane.linux.kernel To: KOSAKI Motohiro CC: Aaditya Kumar , Mel Gorman , KAMEZAWA Hiroyuki , "linux-mm@kvack.org" , LKML Subject: Re: Accounting problem of MIGRATE_ISOLATED freed page References: <4FE169B1.7020600@kernel.org> <4FE16E80.9000306@gmail.com> <4FE18187.3050103@kernel.org> <4FE23069.5030702@gmail.com> <4FE26470.90401@kernel.org> <4FE27F15.8050102@kernel.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5744 Lines: 157 On 06/21/2012 11:45 AM, KOSAKI Motohiro wrote: > On Wed, Jun 20, 2012 at 9:55 PM, Minchan Kim wrote: >> On 06/21/2012 10:39 AM, KOSAKI Motohiro wrote: >> >>>>> number of isolate page block is almost always 0. then if we have such counter, >>>>> we almost always can avoid zone->lock. Just idea. >>>> >>>> Yeb. I thought about it but unfortunately we can't have a counter for MIGRATE_ISOLATE. >>>> Because we have to tweak in page free path for pages which are going to free later after we >>>> mark pageblock type to MIGRATE_ISOLATE. >>> >>> I mean, >>> >>> if (nr_isolate_pageblock != 0) >>> free_pages -= nr_isolated_free_pages(); // your counting logic >>> >>> return __zone_watermark_ok(z, alloc_order, mark, >>> classzone_idx, alloc_flags, free_pages); >>> >>> >>> I don't think this logic affect your race. zone_watermark_ok() is already >>> racy. then new little race is no big matter. >> >> >> It seems my explanation wasn't enough. :( >> I already understand your intention but we can't make nr_isolate_pageblock. >> Because we should count two type of free pages. > > I mean, move_freepages_block increment number of page *block*, not pages. > number of free *pages* are counted by zone_watermark_ok_safe(). > > >> 1. Already freed page so they are already in buddy list. >> Of course, we can count it with return value of move_freepages_block(zone, page, MIGRATE_ISOLATE) easily. >> >> 2. Will be FREEed page by do_migrate_range. >> It's a _PROBLEM_. For it, we should tweak free path. No? > > No. > > >> If All of pages are PageLRU when hot-plug happens(ie, 2), nr_isolate_pagblock is zero and >> zone_watermk_ok_safe can't do his role. > > number of isolate pageblock don't depend on number of free pages. It's > a concept of > an attribute of PFN range. It seems you mean is_migrate_isolate as a just flag, NOT nr_isolate_pageblock. So do you mean this? diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h index 3bdcab3..7f4d19c 100644 --- a/include/linux/page-isolation.h +++ b/include/linux/page-isolation.h @@ -1,6 +1,7 @@ #ifndef __LINUX_PAGEISOLATION_H #define __LINUX_PAGEISOLATION_H +extern bool is_migrate_isolate; /* * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE. * If specified range includes migrate types other than MOVABLE or CMA, diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d2a515d..b997cb3 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1756,6 +1756,27 @@ bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long ma if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark) free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES); +#if defined CONFIG_CMA || CONFIG_MEMORY_HOTPLUG + if (unlikely(is_migrate_isolate)) { + unsigned long flags; + spin_lock_irqsave(&z->lock, flags); + for (order = MAX_ORDER - 1; order >= 0; order--) { + struct free_area *area = &z->free_area[order]; + long count = 0; + struct list_head *curr; + + list_for_each(curr, &area->free_list[MIGRATE_ISOLATE]) + count++; + + free_pages -= (count << order); + if (free_pages < 0) { + free_pages = 0; + break; + } + } + spin_unlock_irqrestore(&z->lock, flags); + } +#endif return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags, free_pages); } diff --git a/mm/page_isolation.c b/mm/page_isolation.c index c9f0477..212e526 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -19,6 +19,8 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages) return pfn_to_page(pfn + i); } +bool is_migrate_isolate = false; + /* * start_isolate_page_range() -- make page-allocation-type of range of pages * to be MIGRATE_ISOLATE. @@ -43,6 +45,8 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn, BUG_ON((start_pfn) & (pageblock_nr_pages - 1)); BUG_ON((end_pfn) & (pageblock_nr_pages - 1)); + is_migrate_isolate = true; + for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) { @@ -59,6 +63,7 @@ undo: pfn += pageblock_nr_pages) unset_migratetype_isolate(pfn_to_page(pfn), migratetype); + is_migrate_isolate = false; return -EBUSY; } @@ -80,6 +85,9 @@ int undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn, continue; unset_migratetype_isolate(page, migratetype); } + + is_migrate_isolate = false; + return 0; } /* It is still racy as you already mentioned and I don't think it's trivial. Direct reclaim can't wake up kswapd forever by current fragile zone->all_unreclaimable. So it's a livelock. Then, do you want to fix this problem by your patch[1]? It could solve the livelock by OOM kill if we apply your patch[1] but still doesn't wake up kswapd although it's not critical. Okay. Then, please write down this problem in detail in your patch's changelog and resend, please. [1] http://lkml.org/lkml/2012/6/14/74 -- Kind regards, Minchan Kim -- 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/