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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id t38sm11324314qtc.12.2019.02.26.11.19.43 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Feb 2019 11:19:43 -0800 (PST) Message-ID: <1551208782.6911.51.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 14:19:42 -0500 In-Reply-To: <20190226182007.GH10588@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> 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 19:20 +0100, Michal Hocko wrote: > Btw. what happens if the offlined pfn range is removed completely? Is > the range still mapped? What kind of consequences does this have? Well, the pages are still marked as reserved as well, so it is up to the physically memory hotplug handler to free kernel direct mapping pagetable, virtual memory mapping pages, and virtual memory mapping pagetable as by design, although I have no way to test it. > Also when does this tweak happens on a completely new hotplugged memory > range? I suppose it will call online_pages() which in-turn call kernel_unmap_linear_page() which may or may not have the same issue, but I have no way to test that path.