From: Johannes Weiner Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0 Date: Fri, 13 May 2011 00:15:06 +0200 Message-ID: <20110512221506.GM16531@cmpxchg.org> References: <1305127773-10570-4-git-send-email-mgorman@suse.de> <1305213359.2575.46.camel@mulgrave.site> <1305214993.2575.50.camel@mulgrave.site> <1305215742.27848.40.camel@jaguar> <1305225467.2575.66.camel@mulgrave.site> <1305229447.2575.71.camel@mulgrave.site> <1305230652.2575.72.camel@mulgrave.site> <1305237882.2575.100.camel@mulgrave.site> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Pekka Enberg , Christoph Lameter , Mel Gorman , Andrew Morton , Colin King , Raghavendra D Prabhu , Jan Kara , Chris Mason , Rik van Riel , linux-fsdevel , linux-mm , linux-kernel , linux-ext4 To: James Bottomley Return-path: Content-Disposition: inline In-Reply-To: <1305237882.2575.100.camel@mulgrave.site> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org On Thu, May 12, 2011 at 05:04:41PM -0500, James Bottomley wrote: > On Thu, 2011-05-12 at 15:04 -0500, James Bottomley wrote: > > Confirmed, I'm afraid ... I can trigger the problem with all three > > patches under PREEMPT. It's not a hang this time, it's just kswapd > > taking 100% system time on 1 CPU and it won't calm down after I unload > > the system. > > Just on a "if you don't know what's wrong poke about and see" basis, I > sliced out all the complex logic in sleeping_prematurely() and, as far > as I can tell, it cures the problem behaviour. I've loaded up the > system, and taken the tar load generator through three runs without > producing a spinning kswapd (this is PREEMPT). I'll try with a > non-PREEMPT kernel shortly. > > What this seems to say is that there's a problem with the complex logic > in sleeping_prematurely(). I'm pretty sure hacking up > sleeping_prematurely() just to dump all the calculations is the wrong > thing to do, but perhaps someone can see what the right thing is ... I think I see the problem: the boolean logic of sleeping_prematurely() is odd. If it returns true, kswapd will keep running. So if pgdat_balanced() returns true, kswapd should go to sleep. This? diff --git a/mm/vmscan.c b/mm/vmscan.c index 2b701e0..092d773 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2261,7 +2261,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining, * must be balanced */ if (order) - return pgdat_balanced(pgdat, balanced, classzone_idx); + return !pgdat_balanced(pgdat, balanced, classzone_idx); else return !all_zones_ok; } -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org