From: Minchan Kim Subject: Re: [PATCH 3/3] mm: slub: Default slub_max_order to 0 Date: Fri, 13 May 2011 14:39:03 +0900 Message-ID: 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> <20110512221506.GM16531@cmpxchg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: James Bottomley , 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: Johannes Weiner Return-path: In-Reply-To: Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org On Fri, May 13, 2011 at 7:58 AM, Minchan Kim wrote: > On Fri, May 13, 2011 at 7:15 AM, Johannes Weiner wro= te: >> 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. =C2=A0It's not a hang this time, it's just ksw= apd >>> > taking 100% system time on 1 CPU and it won't calm down after I unloa= d >>> > 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. =C2=A0I've loaded up the >>> system, and taken the tar load generator through three runs without >>> producing a spinning kswapd (this is PREEMPT). =C2=A0I'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(). =C2=A0I'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. =C2=A0If it returns true, kswapd will keep running. =C2=A0So if >> pgdat_balanced() returns true, kswapd should go to sleep. >> >> This? > > Yes. Good catch. In addition, I see some strange thing. The comment in pgdat_balanced says "Only zones that meet watermarks and are in a zone allowed by the callers classzone_idx are added to balanced_pages" It's true in case of balance_pgdat but it's not true in sleeping_prematurel= y. This? barrios@barrios-desktop:~/linux-mmotm$ git diff mm/vmscan.c diff --git a/mm/vmscan.c b/mm/vmscan.c index 292582c..d9078cf 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2322,7 +2322,8 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining, classzone_idx, 0)) all_zones_ok =3D false; else - balanced +=3D zone->present_pages; + if (i <=3D classzone_idx) + balanced +=3D zone->present_pages; } /* @@ -2331,7 +2332,7 @@ 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; } --=20 Kind regards, Minchan Kim -- 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