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arm64: mm: Implement arch_wants_old_prefaulted_pte()

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On CPUs with hardware AF/DBM, initialising prefaulted PTEs as 'old'
improves vmscan behaviour and does not appear to introduce any overhead
elsewhere.

Implement arch_wants_old_prefaulted_pte() to return 'true' if we detect
hardware access flag support at runtime. This can be extended in future
based on MIDR matching if necessary.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Will Deacon 2020-11-24 18:49:26 +00:00
parent 46bdb4277f
commit 0388f9c743
1 changed files with 11 additions and 1 deletions
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12
arch/arm64/include/asm/pgtable.h
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@ -980,7 +980,17 @@ static inline bool arch_faults_on_old_pte(void)
return !cpu_has_hw_af(); return !cpu_has_hw_af();
} }
#define arch_faults_on_old_pte arch_faults_on_old_pte #define arch_faults_on_old_pte arch_faults_on_old_pte
/*
* Experimentally, it's cheap to set the access flag in hardware and we
* benefit from prefaulting mappings as 'old' to start with.
*/
static inline bool arch_wants_old_prefaulted_pte(void)
{
return !arch_faults_on_old_pte();
}
#define arch_wants_old_prefaulted_pte arch_wants_old_prefaulted_pte
#endif /* !__ASSEMBLY__ */ #endif /* !__ASSEMBLY__ */