From: Wei Xu <weixugc@google.com>
To: "ying.huang@intel.com" <ying.huang@intel.com>
Cc: Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>,
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>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Greg Thelen <gthelen@google.com>, MichalHocko <mhocko@kernel.org>,
Brice Goglin <brice.goglin@gmail.com>
Subject: Re: [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS
Date: Tue, 26 Apr 2022 21:27:01 -0700 [thread overview]
Message-ID: <CAAPL-u_17CveHuWa1JN1NTTUxLCUnXEAdnQwPvigc5BMGa=D1w@mail.gmail.com> (raw)
In-Reply-To: <9a0fe756ae3af78f2612dcf2df9673053a7ebab2.camel@intel.com>
On Tue, Apr 26, 2022 at 1:43 AM ying.huang@intel.com
<ying.huang@intel.com> wrote:
>
> On Mon, 2022-04-25 at 13:39 +0530, Aneesh Kumar K V wrote:
> > On 4/25/22 11:40 AM, ying.huang@intel.com wrote:
> > > On Mon, 2022-04-25 at 09:20 +0530, Aneesh Kumar K.V wrote:
> > > > "ying.huang@intel.com" <ying.huang@intel.com> writes:
> > > >
> > > > > 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.
> > > >
> > > > It is not just that the demotion can be disabled. We should be able to
> > > > use demotion on a system where we can find DRAM only NUMA nodes. That
> > > > cannot be achieved by /sys/kernel/mm/numa/demotion_enabled. It needs
> > > > something similar to to N_DEMOTION_TARGETS
> > > >
> > >
> > > Can you show NUMA information of your machines with DRAM-only nodes and
> > > PMEM nodes? We can try to find the proper demotion order for the
> > > system. If you can not show it, we can defer N_DEMOTION_TARGETS until
> > > the machine is available.
> >
> >
> > Sure will find one such config. As you might have noticed this is very
> > easy to have in a virtualization setup because the hypervisor can assign
> > memory to a guest VM from a numa node that doesn't have CPU assigned to
> > the same guest. This depends on the other guest VM instance config
> > running on the system. So on any virtualization config that has got
> > persistent memory attached, this can become an easy config to end up with.
> >
>
> Why they want to do that? I am looking forward to a real issue, not
> theoritical possibility.
>
> >
> > > > > 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
> > > >
> > > > This is achieved by
> > > >
> > > > [PATCH v2 1/5] mm: demotion: Set demotion list differently
> > > >
> > > > >
> > > > > 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.
> > > > >
> > > > > 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.
> > > >
> > > >
> > > > IMHO the above (2b and 3) can be done using per node demotion targets. Below is
> > > > what I think we could do with a single slow memory NUMA node 4.
> > >
> > > If we can use writable per-node demotion targets as ABI, then we don't
> > > need N_DEMOTION_TARGETS.
> >
> >
> > Not sure I understand that. Yes, once you have a writeable per node
> > demotion target it is easy to build any demotion order.
>
> Yes.
>
> > But that doesn't
> > mean we should not improve the default unless you have reason to say
> > that using N_DEMOTTION_TARGETS breaks any existing config.
> >
>
> Becuase N_DEMOTTION_TARGETS is a new kernel ABI to override the default,
> not the default itself. [1/5] of this patchset improve the default
> behavior itself, and I think that's good.
>
> Because we must maintain the kernel ABI almost for ever, we need to be
> careful about adding new ABI and add less if possible. If writable per-
> node demotion targets can address your issue. Then it's unnecessary to
> add another redundant kernel ABI for that.
I still think the kernel should initialize the per-node demotion order
in a way similar to allocation fallback order and there is no need for
a userspace interface to override per-node demotion order. But I don't
object to such a per-node demotion order override interface proposed
here.
On the other hand, I think it is better to preserve the system-wide
/sys/devices/system/node/demotion_targets as writable. If the
userspace only wants to specify a specific set of nodes as the
demotion tier and is perfectly fine with the per-node demotion order
generated by the kernel, why should we enforce the userspace to have
to manually define the per-node demotion order as well?
> > > > /sys/devices/system/node# cat node[0-4]/demotion_targets
> > > > 4
> > > > 4
> > > > 4
> > > > 4
> > > >
> > > > /sys/devices/system/node# echo 1 > node1/demotion_targets
> > > > bash: echo: write error: Invalid argument
> > > > /sys/devices/system/node# cat node[0-4]/demotion_targets
> > > > 4
> > > > 4
> > > > 4
> > > > 4
> > > >
> > > > /sys/devices/system/node# echo 0 > node1/demotion_targets
> > > > /sys/devices/system/node# cat node[0-4]/demotion_targets
> > > > 4
> > > > 0
> > > > 4
> > > > 4
> > > >
> > > > /sys/devices/system/node# echo 1 > node0/demotion_targets
> > > > bash: echo: write error: Invalid argument
> > > > /sys/devices/system/node# cat node[0-4]/demotion_targets
> > > > 4
> > > > 0
> > > > 4
> > > > 4
> > > >
> > > > Disable demotion for a specific node.
> > > > /sys/devices/system/node# echo > node1/demotion_targets
> > > > /sys/devices/system/node# cat node[0-4]/demotion_targets
> > > > 4
> > > >
> > > > 4
> > > > 4
> > > >
> > > > Reset demotion to default
> > > > /sys/devices/system/node# echo -1 > node1/demotion_targets
> > > > /sys/devices/system/node# cat node[0-4]/demotion_targets
> > > > 4
> > > > 4
> > > > 4
> > > > 4
> > > >
> > > > When a specific device/NUMA node is used for demotion target via the user interface, it is taken
> > > > out of other NUMA node targets.
> > >
> > > IMHO, we should be careful about interaction between auto-generated and
> > > overridden demotion order.
> > >
> >
> > yes, we should avoid loop between that.
>
> In addition to that, we need to get same result after hot-remove then
> hot-add the same node. That is, the result should be stable after NOOP.
> I guess we can just always,
>
> - Generate the default demotion order automatically without any
> overriding.
>
> - Apply the overriding, after removing the invalid targets, etc.
>
> > But if you agree for the above
> > ABI we could go ahead and share the implementation code.
>
> I think we need to add a way to distinguish auto-generated and overriden
> demotion targets in the output of nodeX/demotion_targets. Otherwise it
> looks good to me.
>
> Best Regards,
> Huang, Ying
>
> > > > root@ubuntu-guest:/sys/devices/system/node# cat node[0-4]/demotion_targets
> > > > 4
> > > > 4
> > > > 4
> > > > 4
> > > >
> > > > /sys/devices/system/node# echo 4 > node1/demotion_targets
> > > > /sys/devices/system/node# cat node[0-4]/demotion_targets
> > > >
> > > > 4
> > > >
> > > >
> > > >
> > > > If more than one node requies the same demotion target
> > > > /sys/devices/system/node# echo 4 > node0/demotion_targets
> > > > /sys/devices/system/node# cat node[0-4]/demotion_targets
> > > > 4
> > > > 4
> > > >
> > > >
> > > >
> > > > -aneesh
> > >
> > >
> >
> > -aneesh
>
>
next prev parent reply other threads:[~2022-04-27 4:27 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 [this message]
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
[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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