From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754710AbZKMOid (ORCPT ); Fri, 13 Nov 2009 09:38:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753375AbZKMOic (ORCPT ); Fri, 13 Nov 2009 09:38:32 -0500 Received: from mail-pw0-f42.google.com ([209.85.160.42]:43406 "EHLO mail-pw0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752312AbZKMOib convert rfc822-to-8bit (ORCPT ); Fri, 13 Nov 2009 09:38:31 -0500 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=B9kPYk2DIYAp6ra95NF5E+y4vh1HY+XuVHeXw+eJGTefXp3Ok78WRCXAmPufV2QBKD g7GFN7K5qDexBQb/SuqNmVdDzxFkdrE5Pt1qF12+pKsN0zsT3j0M1TeVfPCn+Mp5Se0E jxmsruF9JJGhNvTK1Qb7mm18gu5I4OtRs4uvU= MIME-Version: 1.0 In-Reply-To: <20091113142608.33B9.A69D9226@jp.fujitsu.com> References: <1258054235-3208-1-git-send-email-mel@csn.ul.ie> <1258054235-3208-6-git-send-email-mel@csn.ul.ie> <20091113142608.33B9.A69D9226@jp.fujitsu.com> Date: Fri, 13 Nov 2009 23:38:37 +0900 Message-ID: <28c262360911130638l7c0becbbsd09db0fd3837ffa5@mail.gmail.com> Subject: Re: [PATCH 5/5] vmscan: Take order into consideration when deciding if kswapd is in trouble From: Minchan Kim To: KOSAKI Motohiro Cc: Mel Gorman , Andrew Morton , Frans Pop , Jiri Kosina , Sven Geggus , Karol Lewandowski , Tobias Oetiker , linux-kernel@vger.kernel.org, "linux-mm@kvack.org\"" , Pekka Enberg , Rik van Riel , Christoph Lameter , Stephan von Krawczynski , "Rafael J. Wysocki" , Kernel Testers List Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Koskai. I missed this patch. I noticed this after Mel reply your patch. On Fri, Nov 13, 2009 at 6:54 PM, KOSAKI Motohiro wrote: >> If reclaim fails to make sufficient progress, the priority is raised. >> Once the priority is higher, kswapd starts waiting on congestion. >> However, on systems with large numbers of high-order atomics due to >> crappy network cards, it's important that kswapd keep working in >> parallel to save their sorry ass. >> >> This patch takes into account the order kswapd is reclaiming at before >> waiting on congestion. The higher the order, the longer it is before >> kswapd considers itself to be in trouble. The impact is that kswapd >> works harder in parallel rather than depending on direct reclaimers or >> atomic allocations to fail. >> >> Signed-off-by: Mel Gorman >> --- >>  mm/vmscan.c |   14 ++++++++++++-- >>  1 files changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index ffa1766..5e200f1 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1946,7 +1946,7 @@ static int sleeping_prematurely(int order, long remaining) >>  static unsigned long balance_pgdat(pg_data_t *pgdat, int order) >>  { >>       int all_zones_ok; >> -     int priority; >> +     int priority, congestion_priority; >>       int i; >>       unsigned long total_scanned; >>       struct reclaim_state *reclaim_state = current->reclaim_state; >> @@ -1967,6 +1967,16 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order) >>        */ >>       int temp_priority[MAX_NR_ZONES]; >> >> +     /* >> +      * When priority reaches congestion_priority, kswapd will sleep >> +      * for a short time while congestion clears. The higher the >> +      * order being reclaimed, the less likely kswapd will go to >> +      * sleep as high-order allocations are harder to reclaim and >> +      * stall direct reclaimers longer >> +      */ >> +     congestion_priority = DEF_PRIORITY - 2; >> +     congestion_priority -= min(congestion_priority, sc.order); > > This calculation mean > >        sc.order        congestion_priority     scan-pages >        --------------------------------------------------------- >        0               10                      1/1024 * zone-mem >        1               9                       1/512  * zone-mem >        2               8                       1/256  * zone-mem >        3               7                       1/128  * zone-mem >        4               6                       1/64   * zone-mem >        5               5                       1/32   * zone-mem >        6               4                       1/16   * zone-mem >        7               3                       1/8    * zone-mem >        8               2                       1/4    * zone-mem >        9               1                       1/2    * zone-mem >        10              0                       1      * zone-mem >        11+             0                       1      * zone-mem > > I feel this is too agressive. The intention of this congestion_wait() > is to prevent kswapd use 100% cpu time. but the above promotion seems > break it. I can't understand your point. Mel didn't change the number of scan pages. It denpends on priority. He just added another one to prevent frequent contestion_wait. Still, shrink_zone is called with priority, not congestion_priority. > example, > ia64 have 256MB hugepage (i.e. order=14). it mean kswapd never sleep. Indeed. Good catch. > example2, > order-3 (i.e. PAGE_ALLOC_COSTLY_ORDER) makes one of most inefficent > reclaim, because it doesn't use lumpy recliam. > I've seen 128GB size zone, it mean 1/128 = 1GB. oh well, kswapd definitely > waste cpu time 100%. Above I said, It depends on priority, not congestion_priority. > >> + >>  loop_again: >>       total_scanned = 0; >>       sc.nr_reclaimed = 0; >> @@ -2092,7 +2102,7 @@ loop_again: >>                * OK, kswapd is getting into trouble.  Take a nap, then take >>                * another pass across the zones. >>                */ >> -             if (total_scanned && priority < DEF_PRIORITY - 2) >> +             if (total_scanned && priority < congestion_priority) >>                       congestion_wait(BLK_RW_ASYNC, HZ/10); > > Instead, How about this? > > > > --- >  mm/vmscan.c |   13 ++++++++++++- >  1 files changed, 12 insertions(+), 1 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 64e4388..937e90d 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1938,6 +1938,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order) >         * free_pages == high_wmark_pages(zone). >         */ >        int temp_priority[MAX_NR_ZONES]; > +       int has_under_min_watermark_zone = 0; Let's make the shorter. How about "under_min_watermark"? > >  loop_again: >        total_scanned = 0; > @@ -2057,6 +2058,15 @@ loop_again: >                        if (total_scanned > SWAP_CLUSTER_MAX * 2 && >                            total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2) >                                sc.may_writepage = 1; > + > +                       /* > +                        * We are still under min water mark. it mean we have > +                        * GFP_ATOMIC allocation failure risk. Hurry up! > +                        */ > +                       if (!zone_watermark_ok(zone, order, min_wmark_pages(zone), > +                                             end_zone, 0)) > +                               has_under_min_watermark_zone = 1; > + >                } >                if (all_zones_ok) >                        break;          /* kswapd: all done */ > @@ -2064,7 +2074,8 @@ loop_again: >                 * OK, kswapd is getting into trouble.  Take a nap, then take >                 * another pass across the zones. >                 */ > -               if (total_scanned && priority < DEF_PRIORITY - 2) > +               if (total_scanned && (priority < DEF_PRIORITY - 2) && > +                   !has_under_min_watermark_zone) >                        congestion_wait(BLK_RW_ASYNC, HZ/10); > >                /* > -- > 1.6.2.5 Anyway, Looks good to me. It's more straightforward than Mel's one, I think. Reviewed-by: Minchan Kim -- Kind regards, Minchan Kim