linux-kernel - Re: [v1 resend 00/12] THP support for zone device page migration

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Message-ID: <09c5ce76-f7c1-41c7-97e1-74448e6143f7@nvidia.com>
Date: Fri, 18 Jul 2025 13:57:13 +1000
From: Balbir Singh <balbirs@...dia.com>
To: Matthew Brost <matthew.brost@...el.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org,
 linux-kernel@...r.kernel.org, Karol Herbst <kherbst@...hat.com>,
 Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...nel.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Jérôme Glisse <jglisse@...hat.com>,
 Shuah Khan <shuah@...nel.org>, David Hildenbrand <david@...hat.com>,
 Barry Song <baohua@...nel.org>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Ryan Roberts <ryan.roberts@....com>, Matthew Wilcox <willy@...radead.org>,
 Peter Xu <peterx@...hat.com>, Zi Yan <ziy@...dia.com>,
 Kefeng Wang <wangkefeng.wang@...wei.com>, Jane Chu <jane.chu@...cle.com>,
 Alistair Popple <apopple@...dia.com>, Donet Tom <donettom@...ux.ibm.com>
Subject: Re: [v1 resend 00/12] THP support for zone device page migration

On 7/18/25 09:40, Matthew Brost wrote:
> On Fri, Jul 04, 2025 at 09:34:59AM +1000, Balbir Singh wrote:
...
>>
>> The nouveau dmem code has been enhanced to use the new THP migration
>> capability.
>>
>> Feedback from the RFC [2]:
>>
> 
> Thanks for the patches, results look very promising. I wanted to give
> some quick feedback:
> 

Are you seeing improvements with the patchset?

> - You appear to have missed updating hmm_range_fault, specifically
> hmm_vma_handle_pmd, to check for device-private entries and populate the
> HMM PFNs accordingly. My colleague François has a fix for this if you're
> interested.
> 

Sure, please feel free to post them. 

> - I believe copy_huge_pmd also needs to be updated to avoid installing a
> migration entry if the swap entry is device-private. I don't have an
> exact fix yet due to my limited experience with core MM. The test case
> that triggers this is fairly simple: fault in a 2MB device page on the
> GPU, then fork a process that reads the page — the kernel crashes in
> this scenario.
> 

I'd be happy to look at any traces you have or post any fixes you have

Thanks for the feedback
Balbir Singh