[PATCH v3 13/13] mm: introduce arch_wants_lazy_mmu_mode()
From: Kevin Brodsky <hidden>
Date: 2025-10-15 08:28:53
Also in:
linux-arm-kernel, linux-mm, lkml, sparclinux, xen-devel
Subsystem:
linux for powerpc (32-bit and 64-bit), memory management - core, the rest · Maintainers:
Madhavan Srinivasan, Michael Ellerman, Andrew Morton, David Hildenbrand, Linus Torvalds
powerpc decides at runtime whether the lazy MMU mode should be used. To avoid the overhead associated with managing task_struct::lazy_mmu_state if the mode isn't used, introduce arch_wants_lazy_mmu_mode() and bail out of lazy_mmu_mode_* if it returns false. Add a default definition returning true, and an appropriate implementation for powerpc. Signed-off-by: Kevin Brodsky <redacted> --- This patch seemed like a good idea to start with, but now I'm not so sure that the churn added to the generic layer is worth it. It provides a minor optimisation for just powerpc. x86 with XEN_PV also chooses at runtime whether to implement lazy_mmu helpers or not, but it doesn't fit this API so neatly and isn't handled here. --- .../include/asm/book3s/64/tlbflush-hash.h | 11 ++++++----- include/linux/pgtable.h | 16 ++++++++++++---- 2 files changed, 18 insertions(+), 9 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
index bbc54690d374..a91b354cf87c 100644
--- a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
+++ b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h@@ -23,10 +23,14 @@ DECLARE_PER_CPU(struct ppc64_tlb_batch, ppc64_tlb_batch); extern void __flush_tlb_pending(struct ppc64_tlb_batch *batch); +#define arch_wants_lazy_mmu_mode arch_wants_lazy_mmu_mode +static inline bool arch_wants_lazy_mmu_mode(void) +{ + return !radix_enabled(); +} + static inline void arch_enter_lazy_mmu_mode(void) { - if (radix_enabled()) - return; /* * apply_to_page_range can call us this preempt enabled when * operating on kernel page tables.
@@ -46,9 +50,6 @@ static inline void arch_flush_lazy_mmu_mode(void) static inline void arch_leave_lazy_mmu_mode(void) { - if (radix_enabled()) - return; - arch_flush_lazy_mmu_mode(); preempt_enable(); }
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 718c9c788114..db4f388d2a16 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h@@ -261,11 +261,19 @@ static inline int pmd_dirty(pmd_t pmd) * currently enabled. */ #ifdef CONFIG_ARCH_LAZY_MMU + +#ifndef arch_wants_lazy_mmu_mode +static inline bool arch_wants_lazy_mmu_mode(void) +{ + return true; +} +#endif + static inline void lazy_mmu_mode_enable(void) { struct lazy_mmu_state *state = ¤t->lazy_mmu_state; - if (in_interrupt()) + if (!arch_wants_lazy_mmu_mode() || in_interrupt()) return; VM_BUG_ON(state->count == U8_MAX);
@@ -283,7 +291,7 @@ static inline void lazy_mmu_mode_disable(void) { struct lazy_mmu_state *state = ¤t->lazy_mmu_state; - if (in_interrupt()) + if (!arch_wants_lazy_mmu_mode() || in_interrupt()) return; VM_BUG_ON(state->count == 0);
@@ -303,7 +311,7 @@ static inline void lazy_mmu_mode_pause(void) { struct lazy_mmu_state *state = ¤t->lazy_mmu_state; - if (in_interrupt()) + if (!arch_wants_lazy_mmu_mode() || in_interrupt()) return; VM_WARN_ON(state->count == 0 || !state->enabled);
@@ -316,7 +324,7 @@ static inline void lazy_mmu_mode_resume(void) { struct lazy_mmu_state *state = ¤t->lazy_mmu_state; - if (in_interrupt()) + if (!arch_wants_lazy_mmu_mode() || in_interrupt()) return; VM_WARN_ON(state->count == 0 || state->enabled);
--
2.47.0