linux-kernel - Re: [RFC PATCH 08/10] mm: hugetlb: disable CMA if liveupdate is enabled

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Message-ID: <86v7hp7zxx.fsf@kernel.org>
Date: Mon, 29 Dec 2025 22:14:50 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: Pratyush Yadav <pratyush@...nel.org>,  Mike Rapoport <rppt@...nel.org>,
  Andrew Morton <akpm@...ux-foundation.org>,  David Hildenbrand
 <david@...nel.org>,  Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,  "Liam
 R. Howlett" <Liam.Howlett@...cle.com>,  Vlastimil Babka <vbabka@...e.cz>,
  Suren Baghdasaryan <surenb@...gle.com>,  Michal Hocko <mhocko@...e.com>,
  Jonathan Corbet <corbet@....net>,  Thomas Gleixner <tglx@...utronix.de>,
  Ingo Molnar <mingo@...hat.com>,  Borislav Petkov <bp@...en8.de>,  Dave
 Hansen <dave.hansen@...ux.intel.com>,  x86@...nel.org,  "H. Peter Anvin"
 <hpa@...or.com>,  Muchun Song <muchun.song@...ux.dev>,  Oscar Salvador
 <osalvador@...e.de>,  Alexander Graf <graf@...zon.com>,  David Matlack
 <dmatlack@...gle.com>,  David Rientjes <rientjes@...gle.com>,  Jason
 Gunthorpe <jgg@...dia.com>,  Samiullah Khawaja <skhawaja@...gle.com>,
  Vipin Sharma <vipinsh@...gle.com>,  Zhu Yanjun <yanjun.zhu@...ux.dev>,
  linux-kernel@...r.kernel.org,  linux-mm@...ck.org,
  linux-doc@...r.kernel.org,  kexec@...ts.infradead.org
Subject: Re: [RFC PATCH 08/10] mm: hugetlb: disable CMA if liveupdate is
 enabled

On Tue, Dec 23 2025, Pasha Tatashin wrote:

> On Sat, Dec 6, 2025 at 6:03 PM Pratyush Yadav <pratyush@...nel.org> wrote:
>>
>> Hugetlb live update support does not yet work with CMA. Print a warning
>> and disable CMA if the config for live updating hugetlb is enabled, and
>> liveupdate is enabled at runtime.
>
> Could you please elaborate this commit to explain why it is not
> supported, and what it would take to support CMA.

The main reason is that when HugeTLB CMA is enabled, the huge pages come
from CMA. If we have preserved pages, we would need to "insert" those
pages into the CMA when they are restored.

CMA does support multiple ranges, so I suppose it can be done, but it
needs some plumbing to work properly.

Will add this in the next revision.

-- 
Regards,
Pratyush Yadav