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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1 Oct 2026, at 6:54, David Hildenbrand (Arm) wrote: > On 9/30/26 17:10, Zi Yan wrote: >> On 30 Sep 2026, at 10:50, Gregory Price wrote: >> >>> On Wed, Sep 30, 2026 at 10:02:23PM +0800, Li Zhe wrote: >>>> The use case is closer to the second one, but the main motivation is not >>>> only startup-time performance.  The more important point is that each >>>> workload has its own DDR/CXL budget assigned by the workload manager. >>>> >>> >>> mempolicy is the wrong interface to do budget policy, you'd be better >>> off looking at Joshua's memcg tiered node solutions for that. >>> >>>> MPOL_WEIGHTED_INTERLEAVE is useful because it lets new allocations >>>> follow that per-workload budget from the beginning, instead of placing >>>> everything on one tier first and correcting the placement later. This is >>>> important for workload orchestration because the workload starts from a >>>> placement close to its assigned DDR/CXL ratio. >>>> >>> >>> This however is reasonable to me - you'd prefer to spread out the cost >>> of initial faulting placement explicitly, rather than simply take >>> fallbacks when the top-tier budget becomes pressured. >>> >>> i.e. w/o interleave: >>> >>> [node 0 ] >>> ^^^^^^^^^^^^^^ alloc until full >>> vvvvvvvvv fallback >>> [node 1 ] >>> >>> in this scenario you end up with considerable hot memory >>> on the remote node consolidated in time-space (everything >>> allocated after node0 becomes full skews heavily toward >>> node1) >>> >>> Tiering then likely takes many faults to rebalance after >>> you've already reached node0 limits. >>> >>> w/ interleave >>> >>> [node 0 ] >>> ^^^vv^^^vv^^^vv^^^vv^^^vv^^^vv.... >>> [node 1 ] >>> >>> In this scenario you do an initial fill distributed by weight >>> and then let tiering figure it out without consolidating all >>> of the pressure to the point where node0 has no space left. >>> >>> That said - this seems like mostly an initial-fill problem, after >>> you initially fill your memory, a new allocation largely implies >>> the memory is hot - and you probably prefer that to be local. >> >> If this is a initial-fill problem, can userspace set weighted interleave >> initially? The program or harness can observe memory usage of the program >> or related NUMA nodes and switch the policy to numa balancing via >> set_mempolicy() or mbind() without MPOL_MF_MOVE after certain threshold >> is met? > > You mean: use the weighted policy initially and then switch to a NUMA-balancing > one which doesn't involve the weights anymore? > > That makes more sense to me. Although I struggle to see why an effectively > "let's put random memory on slow and others at hot" is a good starting point to > later let if be fixed up by actual balancing/tiering. Statistically speaking, unless the hot/cold page distribution follows a power-law distribution, random placement usually provides an average placement result. So it is not a bad start point. > > It all sounds a bit hackish. :) Best Regards, Yan, Zi