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[2003:cb:c702:4b00:c6fa:b613:dbdc:ab]) by smtp.gmail.com with ESMTPSA id o3-20020a05600c4fc300b003ee1e07a14asm1548735wmq.45.2023.04.12.01.38.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Apr 2023 01:38:05 -0700 (PDT) Message-ID: Date: Wed, 12 Apr 2023 10:38:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 To: "Huang, Ying" , Gregory Price Cc: Dragan Stancevic , lsf-pc@lists.linux-foundation.org, nil-migration@lists.linux.dev, linux-cxl@vger.kernel.org, linux-mm@kvack.org References: <5d1156eb-02ae-a6cc-54bb-db3df3ca0597@stancevic.com> <87v8i22abl.fsf@yhuang6-desk2.ccr.corp.intel.com> <87bkjtzu7e.fsf@yhuang6-desk2.ccr.corp.intel.com> From: David Hildenbrand Organization: Red Hat Subject: =?UTF-8?Q?Re=3a_=5bLSF/MM/BPF_TOPIC=5d_BoF_VM_live_migration_over_C?= =?UTF-8?B?WEwgbWVtb3J54oCL?= In-Reply-To: <87bkjtzu7e.fsf@yhuang6-desk2.ccr.corp.intel.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-cxl@vger.kernel.org On 12.04.23 04:54, Huang, Ying wrote: > Gregory Price writes: > >> On Tue, Apr 11, 2023 at 02:37:50PM +0800, Huang, Ying wrote: >>> Gregory Price writes: >>> >>> [snip] >>> >>>> 2. During the migration process, the memory needs to be forced not to be >>>> migrated to another node by other means (tiering software, swap, >>>> etc). The obvious way of doing this would be to migrate and >>>> temporarily pin the page... but going back to problem #1 we see that >>>> ZONE_MOVABLE and Pinning are mutually exclusive. So that's >>>> troublesome. >>> >>> Can we use memory policy (cpusets, mbind(), set_mempolicy(), etc.) to >>> avoid move pages out of CXL.mem node? Now, there are gaps in tiering, >>> but I think it is fixable. >>> >>> Best Regards, >>> Huang, Ying >>> >>> [snip] >> >> That feels like a hack/bodge rather than a proper solution to me. >> >> Maybe this is an affirmative argument for the creation of an EXMEM >> zone. > > Let's start with requirements. What is the requirements for a new zone > type? I'm stills scratching my head regarding this. I keep hearing all different kind of statements that just add more confusions "we want it to be hotunpluggable" "we want to allow for long-term pinning memory" "but we still want it to be movable" "we want to place some unmovable allocations on it". Huh? Just to clarify: ZONE_MOVABLE allows for pinning. It just doesn't allow for long-term pinning of memory. For good reason, because long-term pinning of memory is just the worst (memory waste, fragmentation, overcommit) and instead of finding new ways to *avoid* long-term pinnings, we're coming up with advanced concepts to work-around the fundamental property of long-term pinnings. We want all memory to be long-term pinnable and we want all memory to be movable/hotunpluggable. That's not going to work. If you'd ask me today, my prediction is that ZONE_EXMEM is not going to happen. -- Thanks, David / dhildenb