linux-kernel - Re: [RFC PATCH 10/12] mm/hugetlb: do explicit CMA balancing

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Message-ID: <6c10723cb3da89dad12eb8f8f44ec335bb2680c8.camel@surriel.com>
Date: Wed, 17 Sep 2025 11:21:32 -0400
From: Rik van Riel <riel@...riel.com>
To: Frank van der Linden <fvdl@...gle.com>, akpm@...ux-foundation.org, 
	muchun.song@...ux.dev, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc: hannes@...xchg.org, david@...hat.com, roman.gushchin@...ux.dev
Subject: Re: [RFC PATCH 10/12] mm/hugetlb: do explicit CMA balancing

On Mon, 2025-09-15 at 19:51 +0000, Frank van der Linden wrote:
> CMA areas are normally not very large, but HugeTLB CMA is an
> exception. hugetlb_cma, used for 'gigantic' pages (usually
> 1G), can take up many gigabytes of memory.
> 
> As such, it is potentially the largest source of 'false OOM'
> conditions,

The false OOM kills also seem to happen when a system
does not use hugetlbfs at all, but a cgroup simply has
most/all of its reclaimable memory in a CMA region,
and then tries to do a kernel allocation.

Would it make sense to call hugetlb_cma_balance() from
the pageout code instead, when the pageout code is
trying to free non-CMA memory, but ended up freeing
mostly/only CMA memory?

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