From: "ying.huang@intel.com" <ying.huang@intel.com>
To: Wei Xu <weixugc@google.com>
Cc: Jagdish Gediya <jvgediya@linux.ibm.com>,
Yang Shi <shy828301@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Linux MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Greg Thelen <gthelen@google.com>, MichalHocko <mhocko@kernel.org>,
Brice Goglin <brice.goglin@gmail.com>,
Tim C Chen <tim.c.chen@intel.com>
Subject: Re: [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS
Date: Thu, 28 Apr 2022 16:37:32 +0800 [thread overview]
Message-ID: <cb424fff95cf2b1a6e31616ebb261660e8000425.camel@intel.com> (raw)
In-Reply-To: <CAAPL-u8b3m2yx8A-MhPmJUasuz8Ra9mW2E2dwT2KvJ06FeZofQ@mail.gmail.com>
On Wed, 2022-04-27 at 09:27 -0700, Wei Xu wrote:
> On Wed, Apr 27, 2022 at 12:11 AM ying.huang@intel.com
> <ying.huang@intel.com> wrote:
> >
> > On Mon, 2022-04-25 at 09:56 -0700, Wei Xu wrote:
> > > On Sat, Apr 23, 2022 at 8:02 PM ying.huang@intel.com
> > > <ying.huang@intel.com> wrote:
> > > >
> > > > Hi, All,
> > > >
> > > > On Fri, 2022-04-22 at 16:30 +0530, Jagdish Gediya wrote:
> > > >
> > > > [snip]
> > > >
> > > > > I think it is necessary to either have per node demotion targets
> > > > > configuration or the user space interface supported by this patch
> > > > > series. As we don't have clear consensus on how the user interface
> > > > > should look like, we can defer the per node demotion target set
> > > > > interface to future until the real need arises.
> > > > >
> > > > > Current patch series sets N_DEMOTION_TARGET from dax device kmem
> > > > > driver, it may be possible that some memory node desired as demotion
> > > > > target is not detected in the system from dax-device kmem probe path.
> > > > >
> > > > > It is also possible that some of the dax-devices are not preferred as
> > > > > demotion target e.g. HBM, for such devices, node shouldn't be set to
> > > > > N_DEMOTION_TARGETS. In future, Support should be added to distinguish
> > > > > such dax-devices and not mark them as N_DEMOTION_TARGETS from the
> > > > > kernel, but for now this user space interface will be useful to avoid
> > > > > such devices as demotion targets.
> > > > >
> > > > > We can add read only interface to view per node demotion targets
> > > > > from /sys/devices/system/node/nodeX/demotion_targets, remove
> > > > > duplicated /sys/kernel/mm/numa/demotion_target interface and instead
> > > > > make /sys/devices/system/node/demotion_targets writable.
> > > > >
> > > > > Huang, Wei, Yang,
> > > > > What do you suggest?
> > > >
> > > > We cannot remove a kernel ABI in practice. So we need to make it right
> > > > at the first time. Let's try to collect some information for the kernel
> > > > ABI definitation.
> > > >
> > > > The below is just a starting point, please add your requirements.
> > > >
> > > > 1. Jagdish has some machines with DRAM only NUMA nodes, but they don't
> > > > want to use that as the demotion targets. But I don't think this is a
> > > > issue in practice for now, because demote-in-reclaim is disabled by
> > > > default.
> > > >
> > > > 2. For machines with PMEM installed in only 1 of 2 sockets, for example,
> > > >
> > > > Node 0 & 2 are cpu + dram nodes and node 1 are slow
> > > > memory node near node 0,
> > > >
> > > > available: 3 nodes (0-2)
> > > > node 0 cpus: 0 1
> > > > node 0 size: n MB
> > > > node 0 free: n MB
> > > > node 1 cpus:
> > > > node 1 size: n MB
> > > > node 1 free: n MB
> > > > node 2 cpus: 2 3
> > > > node 2 size: n MB
> > > > node 2 free: n MB
> > > > node distances:
> > > > node 0 1 2
> > > > 0: 10 40 20
> > > > 1: 40 10 80
> > > > 2: 20 80 10
> > > >
> > > > We have 2 choices,
> > > >
> > > > a)
> > > > node demotion targets
> > > > 0 1
> > > > 2 1
> > > >
> > > > b)
> > > > node demotion targets
> > > > 0 1
> > > > 2 X
> > > >
> > > > a) is good to take advantage of PMEM. b) is good to reduce cross-socket
> > > > traffic. Both are OK as defualt configuration. But some users may
> > > > prefer the other one. So we need a user space ABI to override the
> > > > default configuration.
> > >
> > > I think 2(a) should be the system-wide configuration and 2(b) can be
> > > achieved with NUMA mempolicy (which needs to be added to demotion).
> >
> > Unfortunately, some NUMA mempolicy information isn't available at
> > demotion time, for example, mempolicy enforced via set_mempolicy() is
> > for thread. But I think that cpusets can work for demotion.
> >
> > > In general, we can view the demotion order in a way similar to
> > > allocation fallback order (after all, if we don't demote or demotion
> > > lags behind, the allocations will go to these demotion target nodes
> > > according to the allocation fallback order anyway). If we initialize
> > > the demotion order in that way (i.e. every node can demote to any node
> > > in the next tier, and the priority of the target nodes is sorted for
> > > each source node), we don't need per-node demotion order override from
> > > the userspace. What we need is to specify what nodes should be in
> > > each tier and support NUMA mempolicy in demotion.
> >
> > This sounds interesting. Tier sounds like a natural and general concept
> > for these memory types. It's attracting to use it for user space
> > interface too. For example, we may use that for mem_cgroup limits of a
> > specific memory type (tier).
> >
> > And if we take a look at the N_DEMOTION_TARGETS again from the "tier"
> > point of view. The nodes are divided to 2 classes via
> > N_DEMOTION_TARGETS.
> >
> > - The nodes without N_DEMOTION_TARGETS are top tier (or tier 0).
> >
> > - The nodes with N_DEMOTION_TARGETS are non-top tier (or tier 1, 2, 3,
> > ...)
> >
>
> Yes, this is one of the main reasons why we (Google) want this interface.
>
> > So, another possibility is to fit N_DEMOTION_TARGETS and its overriding
> > into "tier" concept too. !N_DEMOTION_TARGETS == TIER0.
> >
> > - All nodes start with TIER0
> >
> > - TIER0 can be cleared for some nodes via e.g. kmem driver
> >
> > TIER0 node list can be read or overriden by the user space via the
> > following interface,
> >
> > /sys/devices/system/node/tier0
> >
> > In the future, if we want to customize more tiers, we can add tier1,
> > tier2, tier3, ..... For now, we can add just tier0. That is, the
> > interface is extensible in the future compared with
> > .../node/demote_targets.
> >
>
> This more explicit tier definition interface works, too.
>
In addition to make tiering definition explicit, more importantly, this
makes it much easier to support more than 2 tiers. For example, for a
system with HBM (High Bandwidth Memory), CPU+DRAM, DRAM only, and PMEM,
that is, 3 tiers, we can put HBM in tier 0, CPU+DRAM and DRAM only in
tier 1, and PMEM in tier 2, automatically, or via user space
overridding. N_DEMOTION_TARGETS isn't natural to be extended to support
this.
Best Regards,
Huang, Ying
> > This isn't as flexible as the writable per-node demotion targets. But
> > it may be enough for most requirements?
>
> I would think so. Besides, it doesn't really conflict with the
> per-node demotion target interface if we really want to introduce the
> latter.
>
> > Best Regards,
> > Huang, Ying
> >
> > > Cross-socket demotion should not be too big a problem in practice
> > > because we can optimize the code to do the demotion from the local CPU
> > > node (i.e. local writes to the target node and remote read from the
> > > source node). The bigger issue is cross-socket memory access onto the
> > > demoted pages from the applications, which is why NUMA mempolicy is
> > > important here.
> > >
> > > > 3. For machines with HBM (High Bandwidth Memory), as in
> > > >
> > > > https://lore.kernel.org/lkml/39cbe02a-d309-443d-54c9-678a0799342d@gmail.com/
> > > >
> > > > > [1] local DDR = 10, remote DDR = 20, local HBM = 31, remote HBM = 41
> > > >
> > > > Although HBM has better performance than DDR, in ACPI SLIT, their
> > > > distance to CPU is longer. We need to provide a way to fix this. The
> > > > user space ABI is one way. The desired result will be to use local DDR
> > > > as demotion targets of local HBM.
> > > >
> > > > Best Regards,
> > > > Huang, Ying
> > > >
> >
> >
> >
next prev parent reply other threads:[~2022-04-28 8:40 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-13 9:22 [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS Jagdish Gediya
2022-04-13 9:22 ` [PATCH v2 1/5] mm: demotion: Set demotion list differently Jagdish Gediya
2022-04-14 7:09 ` ying.huang
2022-04-14 8:48 ` Jagdish Gediya
2022-04-14 8:57 ` ying.huang
2022-04-14 8:55 ` Baolin Wang
2022-04-14 9:02 ` Jonathan Cameron
2022-04-14 10:40 ` Jagdish Gediya
2022-04-21 6:13 ` ying.huang
2022-04-13 9:22 ` [PATCH v2 2/5] mm: demotion: Add new node state N_DEMOTION_TARGETS Jagdish Gediya
2022-04-21 4:33 ` Wei Xu
2022-04-13 9:22 ` [PATCH v2 3/5] mm: demotion: Add support to set targets from userspace Jagdish Gediya
2022-04-21 4:26 ` Wei Xu
2022-04-22 9:13 ` Jagdish Gediya
2022-04-21 5:31 ` Wei Xu
2022-04-13 9:22 ` [PATCH v2 4/5] device-dax/kmem: Set node state as N_DEMOTION_TARGETS Jagdish Gediya
2022-04-13 9:22 ` [PATCH v2 5/5] mm: demotion: Build demotion list based on N_DEMOTION_TARGETS Jagdish Gediya
2022-04-13 21:44 ` [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS Andrew Morton
2022-04-14 10:16 ` Jagdish Gediya
2022-04-14 7:00 ` ying.huang
2022-04-14 10:19 ` Jagdish Gediya
2022-04-21 3:11 ` Yang Shi
2022-04-21 5:41 ` Wei Xu
2022-04-21 6:24 ` ying.huang
2022-04-21 6:49 ` Wei Xu
2022-04-21 7:08 ` ying.huang
2022-04-21 7:29 ` Wei Xu
2022-04-21 7:45 ` ying.huang
2022-04-21 18:26 ` Wei Xu
2022-04-22 0:58 ` ying.huang
2022-04-22 4:46 ` Wei Xu
2022-04-22 5:40 ` ying.huang
2022-04-22 6:13 ` Wei Xu
2022-04-22 6:21 ` ying.huang
2022-04-22 11:00 ` Jagdish Gediya
2022-04-22 16:43 ` Wei Xu
2022-04-22 17:29 ` Yang Shi
2022-04-24 3:02 ` ying.huang
2022-04-25 3:50 ` Aneesh Kumar K.V
2022-04-25 6:10 ` ying.huang
2022-04-25 8:09 ` Aneesh Kumar K V
2022-04-25 8:54 ` Aneesh Kumar K V
2022-04-25 20:17 ` Davidlohr Bueso
2022-04-26 8:42 ` ying.huang
2022-04-26 9:02 ` Aneesh Kumar K V
2022-04-26 9:44 ` ying.huang
2022-04-27 4:27 ` Wei Xu
2022-04-25 7:26 ` Jagdish Gediya
2022-04-25 16:56 ` Wei Xu
2022-04-27 5:06 ` Aneesh Kumar K V
2022-04-27 18:27 ` Wei Xu
2022-04-28 0:56 ` ying.huang
2022-04-28 4:11 ` Wei Xu
2022-04-28 17:14 ` Yang Shi
2022-04-29 1:27 ` Alistair Popple
2022-04-29 2:21 ` ying.huang
2022-04-29 2:58 ` Wei Xu
2022-04-29 3:27 ` ying.huang
2022-04-29 4:45 ` Alistair Popple
2022-04-29 18:53 ` Yang Shi
2022-04-29 18:52 ` Yang Shi
2022-04-27 7:11 ` ying.huang
2022-04-27 16:27 ` Wei Xu
2022-04-28 8:37 ` ying.huang [this message]
[not found] ` <DM6PR11MB4107867291AFE0C210D9052ADCFD9@DM6PR11MB4107.namprd11.prod.outlook.com>
2022-04-30 2:21 ` Wei Xu
2022-04-21 17:56 ` Yang Shi
2022-04-21 23:48 ` ying.huang
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