Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757868Ab2FUKzA (ORCPT ); Thu, 21 Jun 2012 06:55:00 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:56356 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753688Ab2FUKy6 (ORCPT ); Thu, 21 Jun 2012 06:54:58 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.7.4 Message-ID: <4FE2FCFB.4040808@jp.fujitsu.com> Date: Thu, 21 Jun 2012 19:52:43 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.0; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Minchan Kim CC: KOSAKI Motohiro , Aaditya Kumar , Mel Gorman , "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> <4FE2A937.6040701@kernel.org> In-Reply-To: <4FE2A937.6040701@kernel.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6822 Lines: 195 (2012/06/21 13:55), Minchan Kim wrote: > 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. > Hm. I'm sorry if I couldn't chase the disucussion...Can I make summary ? As you shown, it seems to be not difficult to counting free pages under MIGRATE_ISOLATE. And we can know the zone contains MIGRATE_ISOLATE area or not by simple check. for example. == set_pageblock_migratetype(page, MIGRATE_ISOLATE); move_freepages_block(zone, page, MIGRATE_ISOLATE); zone->nr_isolated_areas++; = Then, the solution will be adding a function like following = u64 zone_nr_free_pages(struct zone *zone) { unsigned long free_pages; free_pages = zone_page_state(NR_FREE_PAGES); if (unlikely(z->nr_isolated_areas)) { isolated = count_migrate_isolated_pages(zone); free_pages -= isolated; } return free_pages; } = Right ? and... zone->all_unreclaimable is a different problem ? Thanks, -Kame -- 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/