From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f70.google.com (mail-lf0-f70.google.com [209.85.215.70]) by kanga.kvack.org (Postfix) with ESMTP id D29716B0038 for ; Fri, 30 Dec 2016 02:11:18 -0500 (EST) Received: by mail-lf0-f70.google.com with SMTP id y21so144226870lfa.0 for ; Thu, 29 Dec 2016 23:11:18 -0800 (PST) Received: from mail-lf0-x234.google.com (mail-lf0-x234.google.com. [2a00:1450:4010:c07::234]) by mx.google.com with ESMTPS id p11si32477852lfd.170.2016.12.29.23.11.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Dec 2016 23:11:17 -0800 (PST) Received: by mail-lf0-x234.google.com with SMTP id b14so232707218lfg.2 for ; Thu, 29 Dec 2016 23:11:16 -0800 (PST) From: Michal Nazarewicz Subject: Re: [PATCH] mm: Drop "PFNs busy" printk in an expected path. In-Reply-To: <8737h65nr5.fsf@eliezer.anholt.net> References: <20161229023131.506-1-eric@anholt.net> <20161229091256.GF29208@dhcp22.suse.cz> <87wpeitzld.fsf@eliezer.anholt.net> <8737h65nr5.fsf@eliezer.anholt.net> Date: Fri, 30 Dec 2016 08:11:12 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Eric Anholt , Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-stable , "Robin H. Johnson" , Vlastimil Babka , Marek Szyprowski On Thu, Dec 29 2016, Eric Anholt wrote: > Michal Nazarewicz writes: > >> On Thu, Dec 29 2016, Eric Anholt wrote: >>> Michal Hocko writes: >>> >>>> This has been already brought up >>>> http://lkml.kernel.org/r/20161130092239.GD18437@dhcp22.suse.cz and the= re >>>> was a proposed patch for that which ratelimited the output >>>> http://lkml.kernel.org/r/20161130132848.GG18432@dhcp22.suse.cz resp. >>>> http://lkml.kernel.org/r/robbat2-20161130T195244-998539995Z@orbis-terr= arum.net >>>> >>>> then the email thread just died out because the issue turned out to be= a >>>> configuration issue. Michal indicated that the message might be useful >>>> so dropping it completely seems like a bad idea. I do agree that >>>> something has to be done about that though. Can we reconsider the >>>> ratelimit thing? >>> >>> I agree that the rate of the message has gone up during 4.9 -- it used >>> to be a few per second. >> >> Sounds like a regression which should be fixed. >> >> This is why I don=E2=80=99t think removing the message is a good idea. = If you >> suddenly see a lot of those messages, something changed for the worse. >> If you remove this message, you will never know. >> >>> However, if this is an expected path during normal operation, >> >> This depends on your definition of =E2=80=98expected=E2=80=99 and =E2=80= =98normal=E2=80=99. >> >> In general, I would argue that the fact those ever happen is a bug >> somewhere in the kernel =E2=80=93 if memory is allocated as movable, it = should >> be movable damn it! > > I was taking "expected" from dae803e165a11bc88ca8dbc07a11077caf97bbcb -- > if this is a actually a bug, how do we go about debugging it? That=E2=80=99s why I=E2=80=99ve pointed out that this depends on the defini= tion. In my opinion it=E2=80=99s a design bug which is now nearly impossible to fix in efficient way. The most likely issues is that some subsystem is allocating movable memory but then either does not provide a way to actually move it (that=E2=80=99s an obvious bug in the code IMO) or pins the memory while so= me transaction is performed and at the same time CMA tries to move it. The latter case is really unavoidable at this point which is why this message is =E2=80=98expected=E2=80=99. But if suddenly, the rate of the messages increases dramatically, you have yourself a performance regression. > I've had Raspbian carrying a patch downstream to remove the error > message for 2 years now, and I either need to get this fixed or get this > patch merged to Fedora and Debian as well, now that they're shipping > some support for Raspberry Pi. --=20 Best regards =E3=83=9F=E3=83=8F=E3=82=A6 =E2=80=9C=F0=9D=93=B6=F0=9D=93=B2=F0=9D=93=B7= =F0=9D=93=AA86=E2=80=9D =E3=83=8A=E3=82=B6=E3=83=AC=E3=83=B4=E3=82=A4=E3=83= =84 =C2=ABIf at first you don=E2=80=99t succeed, give up skydiving=C2=BB -- 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