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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Cc:     Gregory Price <gregory.price@memverge.com>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Gregory Price <gourry.memverge@gmail.com>,
        <linux-kernel@vger.kernel.org>, <linux-cxl@vger.kernel.org>,
        <linux-mm@kvack.org>, <akpm@linux-foundation.org>,
        <aneesh.kumar@linux.ibm.com>, <weixugc@google.com>,
        <apopple@nvidia.com>, <tim.c.chen@intel.com>,
        <dave.hansen@intel.com>, <shy828301@gmail.com>,
        <gregkh@linuxfoundation.org>, <rafael@kernel.org>
Subject: Re: [RFC PATCH v3 0/4] Node Weights and Weighted Interleave
In-Reply-To: <20231103141636.000007e4@Huawei.com> (Jonathan Cameron's message
        of "Fri, 3 Nov 2023 14:16:36 +0000")
References: <20231031003810.4532-1-gregory.price@memverge.com>
        <rm43wgtlvwowjolzcf6gj4un4qac4myngxqnd2jwt5yqxree62@t66scnrruttc>
        <20231031152142.GA3029315@cmpxchg.org>
        <jgh5b5bm73qe7m3qmnsjo3drazgfaix3ycqmom5u6tfp6hcerj@ij4vftrutvrt>
        <ZUCCGJgrqqk87aGN@memverge.com>
        <pmxrljwp4ayl3fcu7rxm6prbumgb5l3lwb75lqfipmxxxwnqfo@nb5qjcxw22gp>
        <ZUKDz5NpMsoyzWtZ@memverge.com>
        <a4f5das6ckw5lwj3qv2eaygx4nypb762b6mdnxivrjjndqlhjk@zpjao2ewfdoc>
        <ZUMVI4YG7mB54u0D@memverge.com>
        <87fs1nz3ee.fsf@yhuang6-desk2.ccr.corp.intel.com>
        <20231103141636.000007e4@Huawei.com>
Date:   Mon, 06 Nov 2023 11:20:58 +0800
Message-ID: <8734xjworp.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Jonathan Cameron <Jonathan.Cameron@Huawei.com> writes:

> On Fri, 03 Nov 2023 15:45:13 +0800
> "Huang, Ying" <ying.huang@intel.com> wrote:
>
>> Gregory Price <gregory.price@memverge.com> writes:
>> 
>> > On Thu, Nov 02, 2023 at 10:47:33AM +0100, Michal Hocko wrote:  
>> >> On Wed 01-11-23 12:58:55, Gregory Price wrote:  
>> >> > Basically consider: `numactl --interleave=all ...`
>> >> > 
>> >> > If `--weights=...`: when a node hotplug event occurs, there is no
>> >> > recourse for adding a weight for the new node (it will default to 1).  
>> >> 
>> >> Correct and this is what I was asking about in an earlier email. How
>> >> much do we really need to consider this setup. Is this something nice to
>> >> have or does the nature of the technology requires to be fully dynamic
>> >> and expect new nodes coming up at any moment?
>> >>    
>> >
>> > Dynamic Capacity is expected to cause a numa node to change size (in
>> > number of memory blocks) rather than cause numa nodes to come and go, so
>> > maybe handling the full node hotplug is a bit of an overreach.  
>> 
>> Will node max bandwidth change with the number of memory blocks?
>
> Typically no as even a single memory extent would probably be interleaved
> across all the actual memory devices (think DIMMS for simplicity) within
> a CXL device. I guess a device 'could' do some scaling based on capacity
> provided to a particular host but feels like they should be separate controls.
> I don't recall there being anything in the specification to suggest the
> need to recheck the CDAT info for updates when DC add / remove events happen.

Sounds good!  Thank you for detailed explanation.

> Mind you, who knows in future :)  We'll point out in relevant forums that
> doing so would be very hard to handle cleanly in Linux.

Thanks!

--
Best Regards,
Huang, Ying