From: Alistair Popple <apopple@nvidia.com>
To: Wei Xu <weixugc@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Huang Ying <ying.huang@intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Yang Shi <shy828301@gmail.com>, Linux MM <linux-mm@kvack.org>,
Greg Thelen <gthelen@google.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Jagdish Gediya <jvgediya@linux.ibm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Michal Hocko <mhocko@kernel.org>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Brice Goglin <brice.goglin@gmail.com>,
Feng Tang <feng.tang@intel.com>,
Jonathan.Cameron@huawei.com
Subject: Re: RFC: Memory Tiering Kernel Interfaces
Date: Fri, 06 May 2022 09:57:54 +1000 [thread overview]
Message-ID: <87v8ujh6ow.fsf@nvdebian.thelocal> (raw)
In-Reply-To: <CAAPL-u9sVx94ACSuCVN8V0tKp+AMxiY89cro0japtyB=xNfNBw@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 8235 bytes --]
Wei Xu <weixugc@google.com> writes:
> The current kernel has the basic memory tiering support: Inactive
> pages on a higher tier NUMA node can be migrated (demoted) to a lower
> tier NUMA node to make room for new allocations on the higher tier
> NUMA node. Frequently accessed pages on a lower tier NUMA node can be
> migrated (promoted) to a higher tier NUMA node to improve the
> performance.
>
> A tiering relationship between NUMA nodes in the form of demotion path
> is created during the kernel initialization and updated when a NUMA
> node is hot-added or hot-removed. The current implementation puts all
> nodes with CPU into the top tier, and then builds the tiering hierarchy
> tier-by-tier by establishing the per-node demotion targets based on
> the distances between nodes.
>
> The current memory tiering interface needs to be improved to address
> several important use cases:
>
> * The current tiering initialization code always initializes
> each memory-only NUMA node into a lower tier. But a memory-only
> NUMA node may have a high performance memory device (e.g. a DRAM
> device attached via CXL.mem or a DRAM-backed memory-only node on
> a virtual machine) and should be put into the top tier.
>
> * The current tiering hierarchy always puts CPU nodes into the top
> tier. But on a system with HBM (e.g. GPU memory) devices, these
> memory-only HBM NUMA nodes should be in the top tier, and DRAM nodes
> with CPUs are better to be placed into the next lower tier.
>
> * Also because the current tiering hierarchy always puts CPU nodes
> into the top tier, when a CPU is hot-added (or hot-removed) and
> triggers a memory node from CPU-less into a CPU node (or vice
> versa), the memory tiering hierarchy gets changed, even though no
> memory node is added or removed. This can make the tiering
> hierarchy much less stable.
>
> * A higher tier node can only be demoted to selected nodes on the
> next lower tier, not any other node from the next lower tier. This
> strict, hard-coded demotion order does not work in all use cases
> (e.g. some use cases may want to allow cross-socket demotion to
> another node in the same demotion tier as a fallback when the
> preferred demotion node is out of space), and has resulted in the
> feature request for an interface to override the system-wide,
> per-node demotion order from the userspace.
>
> * There are no interfaces for the userspace to learn about the memory
> tiering hierarchy in order to optimize its memory allocations.
>
> I'd like to propose revised memory tiering kernel interfaces based on
> the discussions in the threads:
>
> - <https://lore.kernel.org/lkml/20220425201728.5kzm4seu7rep7ndr@offworld/T/>
> - <https://lore.kernel.org/linux-mm/20220426114300.00003ad8@Huawei.com/t/>
>
>
> Sysfs Interfaces
> `=============='
>
> * /sys/devices/system/node/memory_tiers
>
> Format: node list (one tier per line, in the tier order)
>
> When read, list memory nodes by tiers.
>
> When written (one tier per line), take the user-provided node-tier
> assignment as the new tiering hierarchy and rebuild the per-node
> demotion order. It is allowed to only override the top tiers, in
> which cases, the kernel will establish the lower tiers automatically.
>
>
> Kernel Representation
> `==================='
>
> * nodemask_t node_states[N_TOPTIER_MEMORY]
>
> Store all top-tier memory nodes.
>
> * nodemask_t memory_tiers[MAX_TIERS]
>
> Store memory nodes by tiers.
>
> * struct demotion_nodes node_demotion[]
>
> where: struct demotion_nodes { nodemask_t preferred; nodemask_t allowed; }
>
> For a node N:
>
> node_demotion[N].preferred lists all preferred demotion targets;
>
> node_demotion[N].allowed lists all allowed demotion targets
> (initialized to be all the nodes in the same demotion tier).
>
>
> Tiering Hierarchy Initialization
> `=============================='
>
> By default, all memory nodes are in the top tier (N_TOPTIER_MEMORY).
>
> A device driver can remove its memory nodes from the top tier, e.g.
> a dax driver can remove PMEM nodes from the top tier.
>
> The kernel builds the memory tiering hierarchy and per-node demotion
> order tier-by-tier starting from N_TOPTIER_MEMORY. For a node N, the
> best distance nodes in the next lower tier are assigned to
> node_demotion[N].preferred and all the nodes in the next lower tier
> are assigned to node_demotion[N].allowed.
>
> node_demotion[N].preferred can be empty if no preferred demotion node
> is available for node N.
>
> If the userspace overrides the tiers via the memory_tiers sysfs
> interface, the kernel then only rebuilds the per-node demotion order
> accordingly.
>
> Memory tiering hierarchy is rebuilt upon hot-add or hot-remove of a
> memory node, but is NOT rebuilt upon hot-add or hot-remove of a CPU
> node.
>
>
> Memory Allocation for Demotion
> `============================'
>
> When allocating a new demotion target page, both a preferred node
> and the allowed nodemask are provided to the allocation function.
> The default kernel allocation fallback order is used to allocate the
> page from the specified node and nodemask.
>
> The memopolicy of cpuset, vma and owner task of the source page can
> be set to refine the demotion nodemask, e.g. to prevent demotion or
> select a particular allowed node as the demotion target.
>
>
> Examples
> `======'
>
> * Example 1:
> Node 0 & 1 are DRAM nodes, node 2 & 3 are PMEM nodes.
>
> Node 0 has node 2 as the preferred demotion target and can also
> fallback demotion to node 3.
>
> Node 1 has node 3 as the preferred demotion target and can also
> fallback demotion to node 2.
>
> Set mempolicy to prevent cross-socket demotion and memory access,
> e.g. cpuset.mems=0,2
>
> node distances:
> node 0 1 2 3
> 0 10 20 30 40
> 1 20 10 40 30
> 2 30 40 10 40
> 3 40 30 40 10
>
> /sys/devices/system/node/memory_tiers
> 0-1
> 2-3
>
> N_TOPTIER_MEMORY: 0-1
>
> node_demotion[]:
> 0: [2], [2-3]
> 1: [3], [2-3]
> 2: [], []
> 3: [], []
>
> * Example 2:
> Node 0 & 1 are DRAM nodes.
> Node 2 is a PMEM node and closer to node 0.
>
> Node 0 has node 2 as the preferred and only demotion target.
>
> Node 1 has no preferred demotion target, but can still demote
> to node 2.
>
> Set mempolicy to prevent cross-socket demotion and memory access,
> e.g. cpuset.mems=0,2
>
> node distances:
> node 0 1 2
> 0 10 20 30
> 1 20 10 40
> 2 30 40 10
>
> /sys/devices/system/node/memory_tiers
> 0-1
> 2
>
> N_TOPTIER_MEMORY: 0-1
>
> node_demotion[]:
> 0: [2], [2]
> 1: [], [2]
> 2: [], []
>
>
> * Example 3:
> Node 0 & 1 are DRAM nodes.
> Node 2 is a PMEM node and has the same distance to node 0 & 1.
>
> Node 0 has node 2 as the preferred and only demotion target.
>
> Node 1 has node 2 as the preferred and only demotion target.
>
> node distances:
> node 0 1 2
> 0 10 20 30
> 1 20 10 30
> 2 30 30 10
>
> /sys/devices/system/node/memory_tiers
> 0-1
> 2
>
> N_TOPTIER_MEMORY: 0-1
>
> node_demotion[]:
> 0: [2], [2]
> 1: [2], [2]
> 2: [], []
>
>
> * Example 4:
> Node 0 & 1 are DRAM nodes, Node 2 is a memory-only DRAM node.
>
> All nodes are top-tier.
>
> node distances:
> node 0 1 2
> 0 10 20 30
> 1 20 10 30
> 2 30 30 10
>
> /sys/devices/system/node/memory_tiers
> 0-2
>
> N_TOPTIER_MEMORY: 0-2
>
> node_demotion[]:
> 0: [], []
> 1: [], []
> 2: [], []
>
>
> * Example 5:
> Node 0 is a DRAM node with CPU.
> Node 1 is a HBM node.
> Node 2 is a PMEM node.
>
> With userspace override, node 1 is the top tier and has node 0 as
> the preferred and only demotion target.
>
> Node 0 is in the second tier, tier 1, and has node 2 as the
> preferred and only demotion target.
>
> Node 2 is in the lowest tier, tier 2, and has no demotion targets.
>
> node distances:
> node 0 1 2
> 0 10 21 30
> 1 21 10 40
> 2 30 40 10
>
> /sys/devices/system/node/memory_tiers (userspace override)
> 1
> 0
> 2
>
> N_TOPTIER_MEMORY: 1
>
> node_demotion[]:
> 0: [2], [2]
> 1: [0], [0]
> 2: [], []
>
> -- Wei
next prev parent reply other threads:[~2022-05-05 23:59 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-30 2:10 RFC: Memory Tiering Kernel Interfaces Wei Xu
2022-04-30 3:59 ` Yang Shi
2022-04-30 6:37 ` Wei Xu
2022-05-06 0:01 ` Alistair Popple
2022-05-10 4:32 ` Wei Xu
2022-05-10 5:37 ` Alistair Popple
2022-05-10 11:38 ` Aneesh Kumar K.V
2022-05-11 5:30 ` Wei Xu
2022-05-11 7:34 ` Alistair Popple
2022-05-11 7:49 ` ying.huang
2022-05-11 17:07 ` Wei Xu
2022-05-12 1:42 ` ying.huang
2022-05-12 2:39 ` Wei Xu
2022-05-12 3:13 ` ying.huang
2022-05-12 3:37 ` Wei Xu
2022-05-12 6:24 ` Wei Xu
2022-05-06 18:56 ` Yang Shi
2022-05-09 14:32 ` Hesham Almatary
2022-05-10 3:24 ` Yang Shi
2022-05-10 9:59 ` Hesham Almatary
2022-05-10 12:10 ` Aneesh Kumar K V
2022-05-11 5:42 ` Wei Xu
2022-05-11 7:12 ` Alistair Popple
2022-05-11 9:05 ` Hesham Almatary
2022-05-12 3:02 ` ying.huang
2022-05-12 4:40 ` Aneesh Kumar K V
2022-05-12 4:49 ` Wei Xu
2022-05-10 4:22 ` Wei Xu
2022-05-10 10:01 ` Hesham Almatary
2022-05-10 11:44 ` Aneesh Kumar K.V
2022-05-01 18:35 ` Dan Williams
2022-05-03 6:36 ` Wei Xu
2022-05-06 19:05 ` Yang Shi
2022-05-07 7:56 ` ying.huang
2022-05-01 17:58 ` Davidlohr Bueso
2022-05-02 1:04 ` David Rientjes
2022-05-02 7:23 ` Aneesh Kumar K.V
2022-05-03 2:07 ` Baolin Wang
2022-05-03 6:06 ` Wei Xu
2022-05-03 17:14 ` Alistair Popple
2022-05-03 17:47 ` Dave Hansen
2022-05-03 22:35 ` Alistair Popple
2022-05-03 23:54 ` Dave Hansen
2022-05-04 1:31 ` Wei Xu
2022-05-04 17:02 ` Dave Hansen
2022-05-05 6:35 ` Wei Xu
2022-05-05 14:24 ` Dave Hansen
2022-05-10 4:43 ` Wei Xu
2022-05-02 6:25 ` Aneesh Kumar K.V
2022-05-03 7:02 ` Wei Xu
2022-05-02 15:20 ` Dave Hansen
2022-05-03 7:19 ` Wei Xu
2022-05-03 19:12 ` Tim Chen
2022-05-05 7:02 ` Wei Xu
2022-05-05 8:57 ` ying.huang
2022-05-05 23:57 ` Alistair Popple [this message]
2022-05-06 0:25 ` Alistair Popple
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