linux-kernel - Re: CXL Boot to Bash - Section 3: Memory (block) Hotplug

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Message-ID: <4ae838ee-b079-408e-8799-e9530ca50417@redhat.com>
Date: Thu, 20 Feb 2025 20:26:21 +0100
From: David Hildenbrand <david@...hat.com>
To: Gregory Price <gourry@...rry.net>, Yang Shi <shy828301@...il.com>
Cc: lsf-pc@...ts.linux-foundation.org, linux-mm@...ck.org,
 linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: CXL Boot to Bash - Section 3: Memory (block) Hotplug

On 20.02.25 19:43, Gregory Price wrote:
> On Thu, Feb 20, 2025 at 09:50:07AM -0800, Yang Shi wrote:
>>>> I will double check that this isn't working as expected, and i'll double
>>>> check for a build option as well.
>>>>
>>>> stupid question - it sorta seems like you'd want this as the default
>>>> setting for driver-managed hotplug memory blocks, but I suppose for
>>>> very small blocks there's problems (as described in the docs).
>>>
>>> The issue is that it is per-memblock. So you'll never have 1 GiB ranges
>>> of consecutive usable memory (e.g., 1 GiB hugetlb page).
>>
>> Regardless of ZONE_MOVABLE or ZONE_NORMAL, right?
>>
>> Thanks,
>> Yang
> 
>  From my testing, yes.

Yes, the only way to get some 1 GiB pages is by using larger memory 
blocks (e.g., 2 GiB on x86-64), which comes with a different set of 
issues (esp. hotplug granularity).

Of course, only 1x usable 1 GiB page for each 2 GiB block.

There were ideas in how to optimize that (e.g., requiring  a new sysfs 
interface to expose variable-sized blocks), if anybody is interested, 
please reach out.

-- 
Cheers,

David / dhildenb