linux-kernel - Re: [RFC PATCH] mm/page_alloc: Add PCP list for THP CMA

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Message-ID: <d66fceb0-4672-4803-b9c9-6b769ff847da@redhat.com>
Date: Tue, 29 Jul 2025 14:42:21 +0200
From: David Hildenbrand <david@...hat.com>
To: "akash.tyagi" <akash.tyagi@...iatek.com>, ziy@...dia.com,
 surenb@...gle.com
Cc: akpm@...ux-foundation.org, vbabka@...e.cz, matthias.bgg@...il.com,
 angelogioacchino.delregno@...labora.com, mhocko@...e.com,
 jackmanb@...gle.com, hannes@...xchg.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org, wsd_upstream@...iatek.com,
 chinwen.chang@...iatek.com
Subject: Re: [RFC PATCH] mm/page_alloc: Add PCP list for THP CMA

On 29.07.25 14:30, akash.tyagi wrote:
> On Fri, 25 Jul 2025 at 10:27, Zi Yan <ziy@...dia.com> wrote:
>> But there is this known problem that CMA can fail temporarily due to
>> short-term pinnings. See the "reliable CMA" work (don't remember the exact name).
>> I think you mean Guaranteed CMA[1].
>>
>> [1] https://lore.kernel.org/linux-mm/CAJuCfpEWVEqsivd7oTvp4foEho_HaD1XNP8KTeKWzG_X2skfGQ@mail.gmail.com/
>>
>> Best Regards,
>> Yan, Zi
> 
> 
> Hi,
> 
> Yes, the issue I described is actually related to Guaranteed CMA[1].
> 
> I have rewritten our problem statement to address concerns more specifically related to the Android common kernels.
> 
> Problem statement:
> Android Common kernels usually have an out-of-tree patch to prevent file-backed page allocated from CMA.
> It allows some allocations which have lower chance of being pinned to use CMA to improve CMA utilization controlled by a flag __GFP_CMA.
> https://lore.kernel.org/lkml/cover.1604282969.git.cgoldswo@codeaurora.org/
> 
> 
> Additionally, android kernels create cma pcp list for pages less than PAGE_ALLOC_COSTLY_ORDER, but not for THP pages.

I'm afraid you have to fix this in the android kernels.

-- 
Cheers,

David / dhildenb