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Wed, 01 Jul 2020 12:50:24 -0700 (PDT) Received: from [2620:15c:17:3:4a0f:cfff:fe51:6667] ([2620:15c:17:3:4a0f:cfff:fe51:6667]) by smtp.gmail.com with ESMTPSA id j19sm5788338pjy.40.2020.07.01.12.50.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2020 12:50:23 -0700 (PDT) Date: Wed, 1 Jul 2020 12:50:23 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Dave Hansen cc: "Huang, Ying" , Yang Shi , Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kbusch@kernel.org, dan.j.williams@intel.com Subject: Re: [RFC][PATCH 3/8] mm/vmscan: Attempt to migrate page in lieu of discard In-Reply-To: <8182ede7-88ce-b891-d100-8c036130797e@intel.com> Message-ID: References: <20200629234503.749E5340@viggo.jf.intel.com> <20200629234509.8F89C4EF@viggo.jf.intel.com> <039a5704-4468-f662-d660-668071842ca3@linux.alibaba.com> <87h7urlioe.fsf@yhuang-dev.intel.com> <8182ede7-88ce-b891-d100-8c036130797e@intel.com> User-Agent: Alpine 2.23 (DEB 453 2020-06-18) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 73C271A4A5 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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, 1 Jul 2020, Dave Hansen wrote: > Even if they don't allocate directly from PMEM, is it OK for such an app > to get its cold data migrated to PMEM? That's a much more subtle > question and I suspect the kernel isn't going to have a single answer > for it. I suspect we'll need a cpuset-level knob to turn auto-demotion > on or off. > I think the answer is whether the app's cold data can be reclaimed, otherwise migration to PMEM is likely better in terms of performance. So any such app today should just be mlocking its cold data if it can't handle overhead from reclaim?