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Re: [PATCH v4 09/12] powerpc/mm: replace batch->active with in_lazy_mmu_mode()
- To: David Hildenbrand <david@xxxxxxxxxx>, linux-mm@xxxxxxxxx
- From: Kevin Brodsky <kevin.brodsky@xxxxxxx>
- Date: Tue, 4 Nov 2025 11:33:03 +0000
- Cc: linux-kernel@xxxxxxxxxxxxxxx, Alexander Gordeev <agordeev@xxxxxxxxxxxxx>, Andreas Larsson <andreas@xxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Christophe Leroy <christophe.leroy@xxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, David Woodhouse <dwmw2@xxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Jann Horn <jannh@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>, Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>, Madhavan Srinivasan <maddy@xxxxxxxxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxx>, Mike Rapoport <rppt@xxxxxxxxxx>, Nicholas Piggin <npiggin@xxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Ryan Roberts <ryan.roberts@xxxxxxx>, Suren Baghdasaryan <surenb@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Vlastimil Babka <vbabka@xxxxxxx>, Will Deacon <will@xxxxxxxxxx>, Yeoreum Yun <yeoreum.yun@xxxxxxx>, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, linuxppc-dev@xxxxxxxxxxxxxxxx, sparclinux@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, x86@xxxxxxxxxx
- Delivery-date: Tue, 04 Nov 2025 11:33:23 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 03/11/2025 16:05, David Hildenbrand wrote:
> On 29.10.25 11:09, Kevin Brodsky wrote:
>> A per-CPU batch struct is activated when entering lazy MMU mode; its
>> lifetime is the same as the lazy MMU section (it is deactivated when
>> leaving the mode). Preemption is disabled in that interval to ensure
>> that the per-CPU reference remains valid.
>>
>> The generic lazy_mmu layer now tracks whether a task is in lazy MMU
>> mode. We can therefore use the generic helper in_lazy_mmu_mode()
>> to tell whether a batch struct is active instead of tracking it
>> explicitly.
>>
>> Signed-off-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
>> ---
>
> I suspect you were not able to test this on real HW. Some help from
> the ppc folks would be appreciated.
Indeed, it would be nice to get some testing on ppc HW that actually
uses lazy MMU (!radix_enabled()).
>
> LGTM, but the interaction with pause/resume adds a bit of complication
> on top.
Does it? This series doesn't change when arch_enter() and arch_leave()
are called, batch->active and in_lazy_mmu_mode() should coincide.
- Kevin
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