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

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Message-ID: <ca0da7fd-245c-4d52-8f4d-f8fce4717494@arm.com>
Date: Wed, 17 Dec 2025 10:01:30 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Kevin Brodsky <kevin.brodsky@....com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Andreas Larsson <andreas@...sler.com>,
 Anshuman Khandual <anshuman.khandual@....com>,
 Boris Ostrovsky <boris.ostrovsky@...cle.com>, Borislav Petkov
 <bp@...en8.de>, Catalin Marinas <catalin.marinas@....com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 David Hildenbrand <david@...hat.com>, "David S. Miller"
 <davem@...emloft.net>, David Woodhouse <dwmw2@...radead.org>,
 "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
 Jann Horn <jannh@...gle.com>, Juergen Gross <jgross@...e.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Michal Hocko <mhocko@...e.com>,
 Mike Rapoport <rppt@...nel.org>, Nicholas Piggin <npiggin@...il.com>,
 Peter Zijlstra <peterz@...radead.org>,
 "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
 Suren Baghdasaryan <surenb@...gle.com>, Thomas Gleixner
 <tglx@...utronix.de>, Venkat Rao Bagalkote <venkat88@...ux.ibm.com>,
 Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
 Yeoreum Yun <yeoreum.yun@....com>, linux-arm-kernel@...ts.infradead.org,
 linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
 xen-devel@...ts.xenproject.org, x86@...nel.org
Subject: Re: [PATCH v6 14/14] mm: Add basic tests for lazy_mmu

On 17/12/2025 09:26, Kevin Brodsky wrote:
> 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.

Does EXPORT_SYMBOL_IF_KUNIT() help?

> 
> - Kevin