From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754209AbZHTMOB (ORCPT ); Thu, 20 Aug 2009 08:14:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754195AbZHTMOA (ORCPT ); Thu, 20 Aug 2009 08:14:00 -0400 Received: from mail-yx0-f175.google.com ([209.85.210.175]:60583 "EHLO mail-yx0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754188AbZHTMN6 convert rfc822-to-8bit (ORCPT ); Thu, 20 Aug 2009 08:13:58 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=fJ/ZKbtvQqI7b965MzQVX+KWYirHR7K8asIrHqu7u/JZl0LAUgwhQ0J+pdGCxIJaRl Z1p+zdPBaqIiilMl7UQDhNLO3+jKa9OQ9LyR/Y8U1PUEZyUHspWd9PW9uRaueDN1MyfM Bla0VBHBqndT8iOACApFLFurxMCu4TanojE+c= MIME-Version: 1.0 In-Reply-To: <20090820114933.GB7359@localhost> References: <20090820024929.GA19793@localhost> <20090820121347.8a886e4b.kamezawa.hiroyu@jp.fujitsu.com> <20090820040533.GA27540@localhost> <28c262360908200401t41c03ad3n114b24e03b61de08@mail.gmail.com> <20090820114933.GB7359@localhost> Date: Thu, 20 Aug 2009 21:13:59 +0900 Message-ID: <28c262360908200513y3fee675do4e1f0204ffb8df63@mail.gmail.com> Subject: Re: [PATCH -v2] mm: do batched scans for mem_cgroup From: Minchan Kim To: Wu Fengguang Cc: KAMEZAWA Hiroyuki , Andrew Morton , Balbir Singh , KOSAKI Motohiro , Rik van Riel , Johannes Weiner , Avi Kivity , Andrea Arcangeli , "Dike, Jeffrey G" , Hugh Dickins , Christoph Lameter , Mel Gorman , LKML , linux-mm , "nishimura@mxp.nes.nec.co.jp" , "lizf@cn.fujitsu.com" , "menage@google.com" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 20, 2009 at 8:49 PM, Wu Fengguang wrote: > On Thu, Aug 20, 2009 at 07:01:21PM +0800, Minchan Kim wrote: >> Hi, Wu. >> >> On Thu, Aug 20, 2009 at 1:05 PM, Wu Fengguang wrote: >> > On Thu, Aug 20, 2009 at 11:13:47AM +0800, KAMEZAWA Hiroyuki wrote: >> >> On Thu, 20 Aug 2009 10:49:29 +0800 >> >> Wu Fengguang wrote: >> >> >> >> > For mem_cgroup, shrink_zone() may call shrink_list() with nr_to_scan=1, >> >> > in which case shrink_list() _still_ calls isolate_pages() with the much >> >> > larger SWAP_CLUSTER_MAX.  It effectively scales up the inactive list >> >> > scan rate by up to 32 times. >> >> > >> >> > For example, with 16k inactive pages and DEF_PRIORITY=12, (16k >> 12)=4. >> >> > So when shrink_zone() expects to scan 4 pages in the active/inactive >> >> > list, it will be scanned SWAP_CLUSTER_MAX=32 pages in effect. >> >> > >> >> > The accesses to nr_saved_scan are not lock protected and so not 100% >> >> > accurate, however we can tolerate small errors and the resulted small >> >> > imbalanced scan rates between zones. >> >> > >> >> > This batching won't blur up the cgroup limits, since it is driven by >> >> > "pages reclaimed" rather than "pages scanned". When shrink_zone() >> >> > decides to cancel (and save) one smallish scan, it may well be called >> >> > again to accumulate up nr_saved_scan. >> >> > >> >> > It could possibly be a problem for some tiny mem_cgroup (which may be >> >> > _full_ scanned too much times in order to accumulate up nr_saved_scan). >> >> > >> >> > CC: Rik van Riel >> >> > CC: Minchan Kim >> >> > CC: Balbir Singh >> >> > CC: KOSAKI Motohiro >> >> > CC: KAMEZAWA Hiroyuki >> >> > Signed-off-by: Wu Fengguang >> >> > --- >> >> >> >> Hmm, how about this ? >> >> == >> >> Now, nr_saved_scan is tied to zone's LRU. >> >> But, considering how vmscan works, it should be tied to reclaim_stat. >> >> >> >> By this, memcg can make use of nr_saved_scan information seamlessly. >> > >> > Good idea, full patch updated with your signed-off-by :) >> > >> > Thanks, >> > Fengguang >> > --- >> > mm: do batched scans for mem_cgroup >> > >> > For mem_cgroup, shrink_zone() may call shrink_list() with nr_to_scan=1, >> > in which case shrink_list() _still_ calls isolate_pages() with the much >> > larger SWAP_CLUSTER_MAX.  It effectively scales up the inactive list >> > scan rate by up to 32 times. >> >> Yes. It can scan 32 times pages in only inactive list, not active list. > > Yes and no ;) > > inactive anon list over scanned => inactive_anon_is_low() == TRUE >                                => shrink_active_list() >                                => active anon list over scanned Why inactive anon list is overscanned in case mem_cgroup ? in shrink_zone, 1) The vm doesn't accumulate nr[l]. 2) Below routine store min value to nr_to_scan. nr_to_scan = min(nr[l], swap_cluster_max); ex) if nr[l] = 4, vm calls shrink_active_list with 4 as nr_to_scan. So I think overscan doesn't occur in active list. > So the end result may be > > - anon inactive  => over scanned > - anon active    => over scanned (maybe not as much) > - file inactive  => over scanned > - file active    => under scanned (relatively) > >> > For example, with 16k inactive pages and DEF_PRIORITY=12, (16k >> 12)=4. >> > So when shrink_zone() expects to scan 4 pages in the active/inactive >> > list, it will be scanned SWAP_CLUSTER_MAX=32 pages in effect. >> >> Active list scan would be scanned in 4,  inactive list  is 32. > > Exactly. > >> > >> > The accesses to nr_saved_scan are not lock protected and so not 100% >> > accurate, however we can tolerate small errors and the resulted small >> > imbalanced scan rates between zones. >> >> Yes. >> >> > This batching won't blur up the cgroup limits, since it is driven by >> > "pages reclaimed" rather than "pages scanned". When shrink_zone() >> > decides to cancel (and save) one smallish scan, it may well be called >> > again to accumulate up nr_saved_scan. >> >> You mean nr_scan_try_batch logic ? >> But that logic works for just global reclaim? >> Now am I missing something? >> >> Could you elaborate more? :) > > Sorry for the confusion. The above paragraph originates from Balbir's > concern: > >        This might be a concern (although not a big ATM), since we can't >        afford to miss limits by much. If a cgroup is near its limit and we >        drop scanning it. We'll have to work out what this means for the end Why does mem_cgroup drops scanning ? It's because nr_scan_try_batch? or something ? Sorry. Still, I can't understand your point. :( >        user. May be more fundamental look through is required at the priority >        based logic of exposing how much to scan, I don't know. > > Thanks, > Fengguang > >> > It could possibly be a problem for some tiny mem_cgroup (which may be >> > _full_ scanned too much times in order to accumulate up nr_saved_scan). >> > >> > CC: Rik van Riel >> > CC: Minchan Kim >> > CC: Balbir Singh >> > CC: KOSAKI Motohiro >> > Signed-off-by: KAMEZAWA Hiroyuki >> > Signed-off-by: Wu Fengguang >> > --- >> >  include/linux/mmzone.h |    6 +++++- >> >  mm/page_alloc.c        |    2 +- >> >  mm/vmscan.c            |   20 +++++++++++--------- >> >  3 files changed, 17 insertions(+), 11 deletions(-) >> > >> > --- linux.orig/include/linux/mmzone.h   2009-07-30 10:45:15.000000000 +0800 >> > +++ linux/include/linux/mmzone.h        2009-08-20 11:51:08.000000000 +0800 >> > @@ -269,6 +269,11 @@ struct zone_reclaim_stat { >> >         */ >> >        unsigned long           recent_rotated[2]; >> >        unsigned long           recent_scanned[2]; >> > + >> > +       /* >> > +        * accumulated for batching >> > +        */ >> > +       unsigned long           nr_saved_scan[NR_LRU_LISTS]; >> >  }; >> > >> >  struct zone { >> > @@ -323,7 +328,6 @@ struct zone { >> >        spinlock_t              lru_lock; >> >        struct zone_lru { >> >                struct list_head list; >> > -               unsigned long nr_saved_scan;    /* accumulated for batching */ >> >        } lru[NR_LRU_LISTS]; >> > >> >        struct zone_reclaim_stat reclaim_stat; >> > --- linux.orig/mm/vmscan.c      2009-08-20 11:48:46.000000000 +0800 >> > +++ linux/mm/vmscan.c   2009-08-20 12:00:55.000000000 +0800 >> > @@ -1521,6 +1521,7 @@ static void shrink_zone(int priority, st >> >        enum lru_list l; >> >        unsigned long nr_reclaimed = sc->nr_reclaimed; >> >        unsigned long swap_cluster_max = sc->swap_cluster_max; >> > +       struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); >> >        int noswap = 0; >> > >> >        /* If we have no swap space, do not bother scanning anon pages. */ >> > @@ -1540,12 +1541,9 @@ static void shrink_zone(int priority, st >> >                        scan >>= priority; >> >                        scan = (scan * percent[file]) / 100; >> >                } >> > -               if (scanning_global_lru(sc)) >> > -                       nr[l] = nr_scan_try_batch(scan, >> > -                                                 &zone->lru[l].nr_saved_scan, >> > -                                                 swap_cluster_max); >> > -               else >> > -                       nr[l] = scan; >> > +               nr[l] = nr_scan_try_batch(scan, >> > +                                         &reclaim_stat->nr_saved_scan[l], >> > +                                         swap_cluster_max); >> >        } >> > >> >        while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || >> > @@ -2128,6 +2126,7 @@ static void shrink_all_zones(unsigned lo >> >  { >> >        struct zone *zone; >> >        unsigned long nr_reclaimed = 0; >> > +       struct zone_reclaim_stat *reclaim_stat; >> > >> >        for_each_populated_zone(zone) { >> >                enum lru_list l; >> > @@ -2144,11 +2143,14 @@ static void shrink_all_zones(unsigned lo >> >                                                l == LRU_ACTIVE_FILE)) >> >                                continue; >> > >> > -                       zone->lru[l].nr_saved_scan += (lru_pages >> prio) + 1; >> > -                       if (zone->lru[l].nr_saved_scan >= nr_pages || pass > 3) { >> > +                       reclaim_stat = get_reclaim_stat(zone, sc); >> > +                       reclaim_stat->nr_saved_scan[l] += >> > +                                               (lru_pages >> prio) + 1; >> > +                       if (reclaim_stat->nr_saved_scan[l] >> > +                                               >= nr_pages || pass > 3) { >> >                                unsigned long nr_to_scan; >> > >> > -                               zone->lru[l].nr_saved_scan = 0; >> > +                               reclaim_stat->nr_saved_scan[l] = 0; >> >                                nr_to_scan = min(nr_pages, lru_pages); >> >                                nr_reclaimed += shrink_list(l, nr_to_scan, zone, >> >                                                                sc, prio); >> > --- linux.orig/mm/page_alloc.c  2009-08-20 11:57:54.000000000 +0800 >> > +++ linux/mm/page_alloc.c       2009-08-20 11:58:39.000000000 +0800 >> > @@ -3716,7 +3716,7 @@ static void __paginginit free_area_init_ >> >                zone_pcp_init(zone); >> >                for_each_lru(l) { >> >                        INIT_LIST_HEAD(&zone->lru[l].list); >> > -                       zone->lru[l].nr_saved_scan = 0; >> > +                       zone->reclaim_stat.nr_saved_scan[l] = 0; >> >                } >> >                zone->reclaim_stat.recent_rotated[0] = 0; >> >                zone->reclaim_stat.recent_rotated[1] = 0; >> > >> > -- >> > 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/ . >> > Don't email: email@kvack.org >> > >> >> >> >> -- >> Kind regards, >> Minchan Kim > -- Kind regards, Minchan Kim