From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f71.google.com (mail-pg0-f71.google.com [74.125.83.71]) by kanga.kvack.org (Postfix) with ESMTP id 60D6F6B0033 for ; Fri, 15 Sep 2017 03:01:08 -0400 (EDT) Received: by mail-pg0-f71.google.com with SMTP id p5so3231606pgn.7 for ; Fri, 15 Sep 2017 00:01:08 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id e2si218687pli.361.2017.09.15.00.01.06 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 15 Sep 2017 00:01:06 -0700 (PDT) Date: Fri, 15 Sep 2017 09:01:00 +0200 From: Michal Hocko Subject: Re: [PATCH] mm/memcg: avoid page count check for zone device Message-ID: <20170915070100.2vuxxxk2zf2yceca@dhcp22.suse.cz> References: <20170914190011.5217-1-jglisse@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170914190011.5217-1-jglisse@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: jglisse@redhat.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Johannes Weiner , Vladimir Davydov 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. > --- > mm/memcontrol.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 15af3da5af02..d51d3e1f49c9 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5648,7 +5648,8 @@ static void uncharge_batch(const struct uncharge_gather *ug) > static void uncharge_page(struct page *page, struct uncharge_gather *ug) > { > VM_BUG_ON_PAGE(PageLRU(page), page); > - VM_BUG_ON_PAGE(!PageHWPoison(page) && page_count(page), page); > + VM_BUG_ON_PAGE(!PageHWPoison(page) && !is_zone_device_page(page) && > + page_count(page), page); > > if (!page->mem_cgroup) > return; > -- > 2.13.5 -- Michal Hocko SUSE Labs -- 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