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[37.188.168.3]) by smtp.gmail.com with ESMTPSA id 185sm7124135wmz.22.2020.06.24.01.50.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jun 2020 01:50:16 -0700 (PDT) Date: Wed, 24 Jun 2020 10:50:15 +0200 From: Michal Hocko To: David Hildenbrand Cc: Wei Yang , akpm@linux-foundation.org, osalvador@suse.de, dan.j.williams@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section Message-ID: <20200624085015.GG1320@dhcp22.suse.cz> References: <20200623094258.6705-1-richard.weiyang@linux.alibaba.com> <20200623151828.GA31426@dhcp22.suse.cz> <57d8a558-dcb3-b318-8e38-6c016b050414@redhat.com> <20200624081324.GA12461@L-31X9LVDL-1304.local> <2b2b722a-58de-4c6e-a04e-dc3516b1b8ab@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2b2b722a-58de-4c6e-a04e-dc3516b1b8ab@redhat.com> X-Rspamd-Queue-Id: 37E9F100ED9E0 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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 Wed 24-06-20 10:41:18, David Hildenbrand wrote: [...] > But nothing actually breaks .... because *drummroll* we use huge pages in the vmemmap, > so the partial depopulate will not actually depopulate anything here. Huge page is 2M, > the memmap of 128MB sections is exactly 2MB == one hugepages. Trying to depopulate a > fraction (e.g., 16MB) of that won't do anything. > > > Now, forcing a CPU without hugepages - PSE (QEMU: "-cpu host,pse=off)", I can trigger > via ndctl create-namespace --force --reconfig=namespace0.0 --mode=devdax --size=16M OK, now I am following! Thanks a lot. That is something to be mentioned in the changelog. Small pages might be used if the hotplug happens on a system with fragmented memory so this is something we do care about. Thanks a lot David! -- Michal Hocko SUSE Labs