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[96.255.20.42]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7cd00f4e1a5sm94081385a.13.2025.05.08.22.50.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 May 2025 22:50:01 -0700 (PDT) Date: Fri, 9 May 2025 01:49:59 -0400 From: Gregory Price To: Rakie Kim Cc: joshua.hahnjy@gmail.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, dan.j.williams@intel.com, ying.huang@linux.alibaba.com, kernel_team@skhynix.com, honggyu.kim@sk.com, yunjeong.mun@sk.com Subject: Re: [RFC] Add per-socket weight support for multi-socket systems in weighted interleave Message-ID: References: <20250509023032.235-1-rakie.kim@sk.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250509023032.235-1-rakie.kim@sk.com> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1560780003 X-Rspam-User: X-Stat-Signature: ftdrgsg7o9zprdnadtkfoadkq9kzzjop X-HE-Tag: 1746769802-791012 X-HE-Meta: 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 OplfjNB5 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 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: List-Subscribe: List-Unsubscribe: On Fri, May 09, 2025 at 11:30:26AM +0900, Rakie Kim wrote: > > Scenario 1: Adapt weighting based on the task's execution node > A task prefers only the DRAM and locally attached CXL memory of the > socket on which it is running, in order to avoid cross-socket access and > optimize bandwidth. > - A task running on CPU0 (node0) would prefer DRAM0 (w=3) and CXL0 (w=1) > - A task running on CPU1 (node1) would prefer DRAM1 (w=3) and CXL1 (w=1) ... snip ... > > However, Scenario 1 does not depend on such information. Rather, it is > a locality-preserving optimization where we isolate memory access to > each socket's DRAM and CXL nodes. I believe this use case is implementable > today and worth considering independently from interconnect performance > awareness. > There's nothing to implement - all the controls exist: 1) --cpunodebind=0 2) --weighted-interleave=0,2 3) cpuset.mems 4) cpuset.cpus You might consider maybe something like "--local-tier" (akin to --localalloc) that sets an explicitly fallback set based on the local node. You'd end up doing something like current_nid = memtier_next_local_node(socket_nid, current_nid) Where this interface returns the preferred fallback ordering but doesn't allow cross-socket fallback. That might be useful, i suppose, in letting a user do: --cpunodebind=0 --weighted-interleave --local-tier without having to know anything about the local memory tier structure. > > At the same time we were discussing this, we were also discussing how to > > do external task-mempolicy modifications - which seemed significantly > > more useful, but ultimately more complex and without sufficient > > interested parties / users. > > I'd like to learn more about that thread. If you happen to have a pointer > to that discussion, it would be really helpful. > https://lore.kernel.org/all/20231122211200.31620-1-gregory.price@memverge.com/ https://lore.kernel.org/all/ZV5zGROLefrsEcHJ@r13-u19.micron.com/ https://lore.kernel.org/linux-mm/ZWYsth2CtC4Ilvoz@memverge.com/ https://lore.kernel.org/linux-mm/20221010094842.4123037-1-hezhongkun.hzk@bytedance.com/ There are locking issues with these that aren't easy to fix. I think the bytedance method uses a task_work queueing to defer a mempolicy update to the task itself the next time it makes a kernel/user transition. That's probably the best overall approach i've seen. https://lore.kernel.org/linux-mm/ZWezcQk+BYEq%2FWiI@memverge.com/ More notes gathered prior to implementing weighted interleave. ~Gregory