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Peter Anvin" , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210203104750.23405-1-osalvador@suse.de> <20210203104750.23405-3-osalvador@suse.de> <20210203141038.GA26693@linux> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Wed, 3 Feb 2021 15:12:05 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20210203141038.GA26693@linux> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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 03.02.21 15:10, Oscar Salvador wrote: > On Wed, Feb 03, 2021 at 02:33:56PM +0100, David Hildenbrand wrote: >> One problem I see with existing code / this change making more obvious is >> that when trying to remove in other granularity than we added (e.g., unplug >> a 128MB DIMM avaialble during boot), we remove the direct map of unrelated >> DIMMs. > > So, let me see if I understand your concern. > > We have a range that was mapped with 1GB page, and we try to remove > a 128MB chunk from it. > Yes, in that case we would clear the pud, and that is bad, so we should > keep the PAGE_ALIGNED checks. > > Now, let us assume that scenario. > If you have a 1GB mapped range and you remove it in smaller chunks bit by bit > (e.g: 128M), the direct mapping of that range will never be cleared unless No, that's exactly what's happening. Good thing is that it barely ever happens, so I assume leaving behind some direct mapping / page tables is not that bad. -- Thanks, David / dhildenb