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[195.135.220.15]) by mx.google.com with ESMTPS id e14si2715242ejs.209.2019.02.12.06.40.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Feb 2019 06:40:27 -0800 (PST) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id BD1BBAF45; Tue, 12 Feb 2019 14:40:26 +0000 (UTC) Date: Tue, 12 Feb 2019 15:40:26 +0100 From: Michal Hocko To: Oscar Salvador Cc: akpm@linux-foundation.org, david@redhat.com, anthony.yznaga@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm,memory_hotplug: Explicitly pass the head to isolate_huge_page Message-ID: <20190212144026.GY15609@dhcp22.suse.cz> References: <20190208090604.975-1-osalvador@suse.de> <20190212083329.GN15609@dhcp22.suse.cz> <20190212134546.gubfir6zzwrvmunr@d104.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190212134546.gubfir6zzwrvmunr@d104.suse.de> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 12-02-19 14:45:49, Oscar Salvador wrote: > On Tue, Feb 12, 2019 at 09:33:29AM +0100, Michal Hocko wrote: > > > > > > if (PageHuge(page)) { > > > struct page *head = compound_head(page); > > > - pfn = page_to_pfn(head) + (1< > > if (compound_order(head) > PFN_SECTION_SHIFT) { > > > ret = -EBUSY; > > > break; > > > } > > > > Why are we doing this, btw? > > I assume you are referring to: > > > > if (compound_order(head) > PFN_SECTION_SHIFT) { > > > ret = -EBUSY; > > > break; > > > } yes. > I thought it was in case we stumble upon a gigantic page, and commit > (c8721bbbdd36 mm: memory-hotplug: enable memory hotplug to handle hugepage) > confirms it. > > But I am not really sure if the above condition would still hold on powerpc, > I wanted to check it but it is a bit more tricky than it is in x86_64 because > of the different hugetlb sizes. > Could it be that the above condition is not true, but still the order of that > hugetlb page goes beyond MAX_ORDER? It is something I have to check. This check doesn't make much sense in principle. Why should we bail out based on a section size? We are offlining a pfn range. All that we care about is whether the hugetlb is migrateable. -- Michal Hocko SUSE Labs