From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id B5DCE6B01FC for ; Tue, 30 Mar 2010 06:17:18 -0400 (EDT) Received: by pzk6 with SMTP id 6so2414805pzk.1 for ; Tue, 30 Mar 2010 03:17:17 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20100330055304.GA2983@sli10-desk.sh.intel.com> References: <20100330055304.GA2983@sli10-desk.sh.intel.com> Date: Tue, 30 Mar 2010 19:17:17 +0900 Message-ID: <28c262361003300317g6df68fc6m4385cfbe3e8a1b04@mail.gmail.com> Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Shaohua Li Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, fengguang.wu@intel.com, kosaki.motohiro@jp.fujitsu.com List-ID: On Tue, Mar 30, 2010 at 2:53 PM, Shaohua Li wrote: > Commit 84b18490d1f1bc7ed5095c929f78bc002eb70f26 introduces a regression. > With it, our tmpfs test always oom. The test has a lot of rotated anon > pages and cause percent[0] zero. Actually the percent[0] is a very small > value, but our calculation round it to zero. The commit makes vmscan > completely skip anon pages and cause oops. > An option is if percent[x] is zero in get_scan_ratio(), forces it > to 1. See below patch. > But the offending commit still changes behavior. Without the commit, we s= can > all pages if priority is zero, below patch doesn't fix this. Don't know i= f > It's required to fix this too. > > Signed-off-by: Shaohua Li > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 79c8098..d5cc34e 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1604,6 +1604,18 @@ static void get_scan_ratio(struct zone *zone, stru= ct scan_control *sc, > =C2=A0 =C2=A0 =C2=A0 =C2=A0/* Normalize to percentages */ > =C2=A0 =C2=A0 =C2=A0 =C2=A0percent[0] =3D 100 * ap / (ap + fp + 1); > =C2=A0 =C2=A0 =C2=A0 =C2=A0percent[1] =3D 100 - percent[0]; > + =C2=A0 =C2=A0 =C2=A0 /* > + =C2=A0 =C2=A0 =C2=A0 =C2=A0* if percent[x] is small and rounded to 0, t= his case doesn't mean we > + =C2=A0 =C2=A0 =C2=A0 =C2=A0* should skip scan. Give it at least 1% shar= e. > + =C2=A0 =C2=A0 =C2=A0 =C2=A0*/ > + =C2=A0 =C2=A0 =C2=A0 if (percent[0] =3D=3D 0) { > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 percent[0] =3D 1; > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 percent[1] =3D 99; > + =C2=A0 =C2=A0 =C2=A0 } > + =C2=A0 =C2=A0 =C2=A0 if (percent[1] =3D=3D 0) { > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 percent[0] =3D 99; > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 percent[1] =3D 1; > + =C2=A0 =C2=A0 =C2=A0 } > =C2=A0} > > =C2=A0/* > Yes. It made subtle change. But we should not depend that change. Current logic seems to be good and clear than old. I think you were lucky at that time by not-good and not-clear logic. BTW, How about this? diff --git a/mm/vmscan.c b/mm/vmscan.c index 79c8098..f0df563 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1646,11 +1646,6 @@ static void shrink_zone(int priority, struct zone *z= one, int file =3D is_file_lru(l); unsigned long scan; - if (percent[file] =3D=3D 0) { - nr[l] =3D 0; - continue; - } - scan =3D zone_nr_lru_pages(zone, sc, l); if (priority) { scan >>=3D priority; --=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/ . Don't email: email@kvack.org