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[195.135.220.15]) by mx.google.com with ESMTPS id n6si1520086edr.330.2019.02.18.10.11.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 18 Feb 2019 10:11:57 -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 E0754AC4C; Mon, 18 Feb 2019 18:11:56 +0000 (UTC) Date: Mon, 18 Feb 2019 19:11:55 +0100 From: Michal Hocko To: Matthew Wilcox Cc: Mike Rapoport , Rong Chen , Pavel Tatashin , linux-kernel@vger.kernel.org, Linux Memory Management List , Andrew Morton , LKP , Oscar Salvador Subject: Re: [LKP] efad4e475c [ 40.308255] Oops: 0000 [#1] PREEMPT SMP PTI Message-ID: <20190218181155.GC4525@dhcp22.suse.cz> References: <20190218070844.GC4525@dhcp22.suse.cz> <20190218085510.GC7251@dhcp22.suse.cz> <4c75d424-2c51-0d7d-5c28-78c15600e93c@intel.com> <20190218103013.GK4525@dhcp22.suse.cz> <20190218140515.GF25446@rapoport-lnx> <20190218152050.GS4525@dhcp22.suse.cz> <20190218152213.GT4525@dhcp22.suse.cz> <20190218164813.GG25446@rapoport-lnx> <20190218170558.GV4525@dhcp22.suse.cz> <20190218175726.GU12668@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190218175726.GU12668@bombadil.infradead.org> 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 Mon 18-02-19 09:57:26, Matthew Wilcox wrote: > On Mon, Feb 18, 2019 at 06:05:58PM +0100, Michal Hocko wrote: > > + end_pfn = min(start_pfn + nr_pages, > > + zone_end_pfn(page_zone(pfn_to_page(start_pfn)))); > > > > /* Check the starting page of each pageblock within the range */ > > - for (; page < end_page; page = next_active_pageblock(page)) { > > - if (!is_pageblock_removable_nolock(page)) > > + for (; start_pfn < end_pfn; start_pfn = next_active_pageblock(start_pfn)) { > > + if (!is_pageblock_removable_nolock(start_pfn)) > > If you have a zone which contains pfns that run from ULONG_MAX-n to ULONG_MAX, > end_pfn is going to wrap around to 0 and this loop won't execute. Is this a realistic situation to bother? > I think > you should use: > > max_pfn = min(start_pfn + nr_pages, > zone_end_pfn(page_zone(pfn_to_page(start_pfn)))) - 1; > > for (; start_pfn <= max_pfn; ...) I do not really care strongly, but we have more places were we do start_pfn + nr_pages and then use it as pfn < end_pfn construct. I suspect we would need to make a larger audit and make the code consistent so unless there are major concerns I would stick with what I have for now and leave the rest for the cleanup. Does that sound reasonable? -- Michal Hocko SUSE Labs