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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id m128sm7927982qkf.53.2019.02.26.12.10.39 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Feb 2019 12:10:40 -0800 (PST) Message-ID: <1551211839.6911.54.camel@lca.pw> Subject: Re: [PATCH] mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC From: Qian Cai To: Michal Hocko Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Tue, 26 Feb 2019 15:10:39 -0500 In-Reply-To: <20190226194024.GI10588@dhcp22.suse.cz> References: <20190225191710.48131-1-cai@lca.pw> <20190226123521.GZ10588@dhcp22.suse.cz> <4d4d3140-6d83-6d22-efdb-370351023aea@lca.pw> <20190226142352.GC10588@dhcp22.suse.cz> <1551203585.6911.47.camel@lca.pw> <20190226181648.GG10588@dhcp22.suse.cz> <20190226182007.GH10588@dhcp22.suse.cz> <1551208782.6911.51.camel@lca.pw> <20190226194024.GI10588@dhcp22.suse.cz> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit 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, 2019-02-26 at 20:40 +0100, Michal Hocko wrote: > It seems you have missed the point of my question. It simply doesn't > make much sense to have offline memory mapped. That memory is not > accessible in general. So mapping it at the offline time is dubious at > best. Well, kernel_map_pages() is like other debug features which could look "unusual". > Also you do not get through the offlining phase on a newly > hotplugged (and not yet onlined) memory. So the patch doesn't look > correct to me and it all smells like the bug you are seeing is a wrong > reporting. > That (physical memory hotadd) is a special case like during the boot. The patch is strictly to deal with offline/online memory, i.e., logical/soft memory hotplug.