linux-kernel - Re: [External] Re: [PATCH v1 0/1] Improved Memory Tier Creation for CPUless NUMA Nodes

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Date: Tue, 05 Mar 2024 15:37:10 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: "Ho-Ren (Jack) Chuang" <horenchuang@...edance.com>
Cc: Gregory Price <gourry.memverge@...il.com>,  aneesh.kumar@...ux.ibm.com,
  mhocko@...e.com,  tj@...nel.org,  john@...alactic.com,  Eishan Mirakhur
 <emirakhur@...ron.com>,  Vinicius Tavares Petrucci
 <vtavarespetr@...ron.com>,  Ravis OpenSrc <Ravis.OpenSrc@...ron.com>,
  Alistair Popple <apopple@...dia.com>,  "Rafael J. Wysocki"
 <rafael@...nel.org>,  Len Brown <lenb@...nel.org>,  Andrew Morton
 <akpm@...ux-foundation.org>,  Dave Jiang <dave.jiang@...el.com>,  Dan
 Williams <dan.j.williams@...el.com>,  Jonathan Cameron
 <Jonathan.Cameron@...wei.com>,  linux-acpi@...r.kernel.org,
  linux-kernel@...r.kernel.org,  linux-mm@...ck.org,  "Ho-Ren (Jack)
 Chuang" <horenc@...edu>,  "Ho-Ren (Jack) Chuang" <horenchuang@...il.com>,
  linux-cxl@...r.kernel.org,  qemu-devel@...gnu.org
Subject: Re: [External] Re: [PATCH v1 0/1] Improved Memory Tier Creation for
 CPUless NUMA Nodes

"Ho-Ren (Jack) Chuang" <horenchuang@...edance.com> writes:

> On Mon, Mar 4, 2024 at 10:36 PM Huang, Ying <ying.huang@...el.com> wrote:
>>
>> "Ho-Ren (Jack) Chuang" <horenchuang@...edance.com> writes:
>>
>> > On Sun, Mar 3, 2024 at 6:47 PM Huang, Ying <ying.huang@...el.com> wrote:
>> >>
>> >> "Ho-Ren (Jack) Chuang" <horenchuang@...edance.com> writes:
>> >>
>> >> > The memory tiering component in the kernel is functionally useless for
>> >> > CPUless memory/non-DRAM devices like CXL1.1 type3 memory because the nodes
>> >> > are lumped together in the DRAM tier.
>> >> > https://lore.kernel.org/linux-mm/PH0PR08MB7955E9F08CCB64F23963B5C3A860A@PH0PR08MB7955.namprd08.prod.outlook.com/T/
>> >>
>> >> I think that it's unfair to call it "useless".  Yes, it doesn't work if
>> >> the CXL memory device are not enumerate via drivers/dax/kmem.c.  So,
>> >> please be specific about in which cases it doesn't work instead of too
>> >> general "useless".
>> >>
>> >
>> > Thank you and I didn't mean anything specific. I simply reused phrases
>> > we discussed
>> > earlier in the previous patchset. I will change them to the following in v2:
>> > "At boot time, current memory tiering assigns all detected memory nodes
>> > to the same DRAM tier. This results in CPUless memory/non-DRAM devices,
>> > such as CXL1.1 type3 memory, being unable to be assigned to the
>> > correct memory tier,
>> > leading to the inability to migrate pages between different types of memory."
>> >
>> > Please see if this looks more specific.
>>
>> I don't think that the description above is accurate.  In fact, there
>> are 2 ways to enumerate the memory device,
>>
>> 1. Mark it as reserved memory (E820_TYPE_SOFT_RESERVED, etc.) in E820
>>    table or something similar.
>>
>> 2. Mark it as normal memory (E820_TYPE_RAM) in E820 table or something
>>    similar
>>
>> For 1, the memory device (including CXL memory) is onlined via
>> drivers/dax/kmem.c, so will be put in proper memory tiers.  For 2, the
>> memory device is indistinguishable with normal DRAM with current
>> implementation.  And this is what this patch is working on.
>>
>> Right?
>
> Good point! How about this?:
> "
> When a memory device, such as CXL1.1 type3 memory, is emulated as
> normal memory (E820_TYPE_RAM), the memory device is indistinguishable
> from normal DRAM in terms of memory tiering with the current implementation.
> The current memory tiering assigns all detected normal memory nodes
> to the same DRAM tier. This results in normal memory devices with
> different attributions being unable to be assigned to the correct memory tier,
> leading to the inability to migrate pages between different types of memory.
> "

Looks good me!  Thanks!

--
Best Regards,
Huang, Ying