From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f199.google.com (mail-io0-f199.google.com [209.85.223.199]) by kanga.kvack.org (Postfix) with ESMTP id B75146B0038 for ; Sun, 17 Sep 2017 13:45:42 -0400 (EDT) Received: by mail-io0-f199.google.com with SMTP id q7so13405326ioi.3 for ; Sun, 17 Sep 2017 10:45:42 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id u134si3360612oif.186.2017.09.17.10.45.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 17 Sep 2017 10:45:41 -0700 (PDT) Date: Sun, 17 Sep 2017 10:45:34 -0700 From: Jerome Glisse Subject: Re: [PATCH] mm/memcg: avoid page count check for zone device Message-ID: <20170917174534.GC11906@redhat.com> References: <20170914190011.5217-1-jglisse@redhat.com> <20170915070100.2vuxxxk2zf2yceca@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170915070100.2vuxxxk2zf2yceca@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Johannes Weiner , Vladimir Davydov On Fri, Sep 15, 2017 at 09:01:00AM +0200, Michal Hocko wrote: > On Thu 14-09-17 15:00:11, jglisse@redhat.com wrote: > > From: Jerome Glisse > > > > Fix for 4.14, zone device page always have an elevated refcount > > of one and thus page count sanity check in uncharge_page() is > > inappropriate for them. > > > > Signed-off-by: Jerome Glisse > > Reported-by: Evgeny Baskakov > > Cc: Andrew Morton > > Cc: Johannes Weiner > > Cc: Michal Hocko > > Cc: Vladimir Davydov > > Acked-by: Michal Hocko > > Side note. Wouldn't it be better to re-organize the check a bit? It is > true that this is VM_BUG so it is not usually compiled in but when it > preferably checks for unlikely cases first while the ref count will be > 0 in the prevailing cases. So can we have > VM_BUG_ON_PAGE(page_count(page) && !is_zone_device_page(page) && > !PageHWPoison(page), page); > > I would simply fold this nano optimization into the patch as you are > touching it already. Not sure it is worth a separate commit. I am traveling sorry for late answer. This nano optimization make sense Andrew do you want me to respin or should we leave it be ? I don't mind either way. Cheers, Jerome -- 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