linux-kernel - Re: [PATCH v6 14/14] mm: Add basic tests for lazy

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Message-ID: <f9550d22-8810-4145-aaa8-48961f6ea35e@arm.com>
Date: Wed, 17 Dec 2025 10:26:12 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
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Subject: Re: [PATCH v6 14/14] mm: Add basic tests for lazy_mmu

On 17/12/2025 05:14, Andrew Morton wrote:
> On Mon, 15 Dec 2025 15:03:23 +0000 Kevin Brodsky <kevin.brodsky@....com> wrote:
>
>> Add basic KUnit tests for the generic aspects of the lazy MMU mode:
>> ensure that it appears active when it should, depending on how
>> enable/disable and pause/resume pairs are nested.
> I needed this for powerpc allmodconfig;
>
> --- a/arch/powerpc/mm/book3s64/hash_tlb.c~mm-add-basic-tests-for-lazy_mmu-fix
> +++ a/arch/powerpc/mm/book3s64/hash_tlb.c
> @@ -30,6 +30,7 @@
>  #include <trace/events/thp.h>
>  
>  DEFINE_PER_CPU(struct ppc64_tlb_batch, ppc64_tlb_batch);
> +EXPORT_SYMBOL_GPL(ppc64_tlb_batch);
>  
>  /*
>   * A linux PTE was changed and the corresponding hash table entry
> @@ -154,6 +155,7 @@ void __flush_tlb_pending(struct ppc64_tl
>  		flush_hash_range(i, local);
>  	batch->index = 0;
>  }
> +EXPORT_SYMBOL_GPL(__flush_tlb_pending);
>  
>  void hash__tlb_flush(struct mmu_gather *tlb)
>  {
> _

Oh indeed I hadn't considered that arch_{enter,leave}_lazy_mmu_mode()
refer to those symbols on powerpc... Maybe a bit overkill to export
those just for a test module, but I'm not sure there's a good
alternative. Forcing LAZY_MMU_MODE_KUNIT_TEST=y is ugly as it would also
force KUNIT=y. Alternatively we could depend on !PPC, not pretty either.

- Kevin