linux-kernel - Re: [PATCH 7/7] mm: update lazy

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Message-ID: <aLrF7qi85tmHfWRf@kernel.org>
Date: Fri, 5 Sep 2025 14:13:50 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Andreas Larsson <andreas@...sler.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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>,
	"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>, Nicholas Piggin <npiggin@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
	linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
	sparclinux@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 7/7] mm: update lazy_mmu documentation

On Thu, Sep 04, 2025 at 01:57:36PM +0100, Kevin Brodsky wrote:
> We now support nested lazy_mmu sections on all architectures
> implementing the API. Update the API comment accordingly.
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>

Acked-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
>  include/linux/pgtable.h | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 6932c8e344ab..be0f059beb4d 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -228,8 +228,18 @@ static inline int pmd_dirty(pmd_t pmd)
>   * of the lazy mode. So the implementation must assume preemption may be enabled
>   * and cpu migration is possible; it must take steps to be robust against this.
>   * (In practice, for user PTE updates, the appropriate page table lock(s) are
> - * held, but for kernel PTE updates, no lock is held). Nesting is not permitted
> - * and the mode cannot be used in interrupt context.
> + * held, but for kernel PTE updates, no lock is held). The mode cannot be used
> + * in interrupt context.
> + *
> + * Calls may be nested: an arch_{enter,leave}_lazy_mmu_mode() pair may be called
> + * while the lazy MMU mode has already been enabled. An implementation should
> + * handle this using the state returned by enter() and taken by the matching
> + * leave() call; the LAZY_MMU_{DEFAULT,NESTED} flags can be used to indicate
> + * whether this enter/leave pair is nested inside another or not. (It is up to
> + * the implementation to track whether the lazy MMU mode is enabled at any point
> + * in time.) The expectation is that leave() will flush any batched state
> + * unconditionally, but only leave the lazy MMU mode if the passed state is not
> + * LAZY_MMU_NESTED.
>   */
>  #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
>  typedef int lazy_mmu_state_t;
> -- 
> 2.47.0
> 

-- 
Sincerely yours,
Mike.