From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755015AbZKMOs6 (ORCPT ); Fri, 13 Nov 2009 09:48:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752900AbZKMOsx (ORCPT ); Fri, 13 Nov 2009 09:48:53 -0500 Received: from mail-pw0-f42.google.com ([209.85.160.42]:39459 "EHLO mail-pw0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752779AbZKMOsw convert rfc822-to-8bit (ORCPT ); Fri, 13 Nov 2009 09:48:52 -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=CujZ2yMw6/3OCFxU2XQ1F8/REUHvXdV15VClaKYGpES1M6t0n8zkwjHCE2LKmqtmsP 4iiiIC0k7k+dfVvZfuk9AXKPMa4pKEXaBWRcY8xghJjkZWNmIHIw72TuWr5Cw+jFTHYU 5P6pmAEYnFvsBFOaFFEKTXc8z1QcBLdpzUgPM= MIME-Version: 1.0 In-Reply-To: <20091113135443.GF29804@csn.ul.ie> 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> <20091113135443.GF29804@csn.ul.ie> Date: Fri, 13 Nov 2009 23:48:57 +0900 Message-ID: <28c262360911130648q7b615ad4if75b902ed25d5fbd@mail.gmail.com> Subject: Re: [PATCH 5/5] vmscan: Take order into consideration when deciding if kswapd is in trouble From: Minchan Kim To: Mel Gorman Cc: KOSAKI Motohiro , 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 On Fri, Nov 13, 2009 at 10:54 PM, Mel Gorman wrote: > On Fri, Nov 13, 2009 at 06:54:29PM +0900, 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. As I said in reply of kosaki's patch, I can't understand point. > Ok, I thought the intention might be to avoid dumping too many pages on > the queue but it was already waiting on congestion elsewhere. > >> but the above promotion seems >> break it. >> >> example, >> ia64 have 256MB hugepage (i.e. order=14). it mean kswapd never sleep. >> example2, But, This is a true problem missed in my review. Thanks, Kosaki. >> 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%. >> >> >> > + >> >  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? >> > > This makes a lot of sense. Tests look good and I added stats to make sure > the logic was triggering. On X86, kswapd avoided a congestion_wait 11723 > times and X86-64 avoided it 5084 times. I think we should hold onto the > stats temporarily until all these bugs are ironed out. > > Would you like to sign off the following? > > If you are ok to sign off, this patch should replace my patch 5 in > the series. I agree Kosaki's patch is more strightforward. You can add my review sign, too. Thanks for good patch, Kosaki. :) -- Kind regards, Minchan Kim