From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id C1AF06B7509 for ; Wed, 5 Dec 2018 10:37:36 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id v4so9774840edm.18 for ; Wed, 05 Dec 2018 07:37:36 -0800 (PST) Received: from outbound-smtp12.blacknight.com (outbound-smtp12.blacknight.com. [46.22.139.17]) by mx.google.com with ESMTPS id a15si396094eds.294.2018.12.05.07.37.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 05 Dec 2018 07:37:35 -0800 (PST) Received: from mail.blacknight.com (pemlinmail02.blacknight.ie [81.17.254.11]) by outbound-smtp12.blacknight.com (Postfix) with ESMTPS id 068171C25C0 for ; Wed, 5 Dec 2018 15:37:35 +0000 (GMT) Date: Wed, 5 Dec 2018 15:37:33 +0000 From: Mel Gorman Subject: Re: [PATCH 1/2] mm, pageblock: make sure pageblock won't exceed mem_sectioin Message-ID: <20181205153733.GB23260@techsingularity.net> References: <20181205091905.27727-1-richard.weiyang@gmail.com> <20181205111513.GA23260@techsingularity.net> <20181205120820.3gbhfvxgmclvj3wu@master> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20181205120820.3gbhfvxgmclvj3wu@master> Sender: owner-linux-mm@kvack.org List-ID: To: Wei Yang Cc: linux-mm@kvack.org, akpm@linux-foundation.org On Wed, Dec 05, 2018 at 12:08:20PM +0000, Wei Yang wrote: > On Wed, Dec 05, 2018 at 11:15:13AM +0000, Mel Gorman wrote: > >On Wed, Dec 05, 2018 at 05:19:04PM +0800, Wei Yang wrote: > >> When SPARSEMEM is used, there is an indication that pageblock is not > >> allowed to exceed one mem_section. Current code doesn't have this > >> constrain explicitly. > >> > >> This patch adds this to make sure it won't. > >> > >> Signed-off-by: Wei Yang > > > >Is this even possible? This would imply that the section size is smaller > >than max order which would be quite a crazy selection for a sparesemem > >section size. A lot of assumptions on the validity of PFNs within a > >max-order boundary would be broken with such a section size. I'd be > >surprised if such a setup could even boot, let alone run. > > pageblock_order has two definitions. > > #define pageblock_order HUGETLB_PAGE_ORDER > > #define pageblock_order (MAX_ORDER-1) > > If CONFIG_HUGETLB_PAGE is not enabled, pageblock_order is related to > MAX_ORDER, which ensures it is smaller than section size. > > If CONFIG_HUGETLB_PAGE is enabled, pageblock_order is not related to > MAX_ORDER. I don't see HUGETLB_PAGE_ORDER is ensured to be less than > section size. Maybe I missed it? > HUGETLB_PAGE_ORDER is less than MAX_ORDER on the basis that normal huge pages (not gigantic) pages are served from the buddy allocator which is limited by MAX_ORDER. -- Mel Gorman SUSE Labs