diff options
| author | Nadav Amit <[email protected]> | 2022-05-09 18:20:50 -0700 |
|---|---|---|
| committer | Andrew Morton <[email protected]> | 2022-05-13 07:20:05 -0700 |
| commit | 4f83145721f362c2f4d312edc4755269a2069488 (patch) | |
| tree | 4a13cb87519b0bd3659d91f6f3a19df4575d4f96 /arch/x86/mm/pgtable.c | |
| parent | c9fe66560bf2dc7d109754414e309888cb8c9ba9 (diff) | |
mm: avoid unnecessary flush on change_huge_pmd()
Calls to change_protection_range() on THP can trigger, at least on x86,
two TLB flushes for one page: one immediately, when pmdp_invalidate() is
called by change_huge_pmd(), and then another one later (that can be
batched) when change_protection_range() finishes.
The first TLB flush is only necessary to prevent the dirty bit (and with a
lesser importance the access bit) from changing while the PTE is modified.
However, this is not necessary as the x86 CPUs set the dirty-bit
atomically with an additional check that the PTE is (still) present. One
caveat is Intel's Knights Landing that has a bug and does not do so.
Leverage this behavior to eliminate the unnecessary TLB flush in
change_huge_pmd(). Introduce a new arch specific pmdp_invalidate_ad()
that only invalidates the access and dirty bit from further changes.
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Nadav Amit <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andrew Cooper <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yu Zhao <[email protected]>
Cc: Nick Piggin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Diffstat (limited to 'arch/x86/mm/pgtable.c')
| -rw-r--r-- | arch/x86/mm/pgtable.c | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index 3481b35cb4ec..f16059e9a85e 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -608,6 +608,16 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma, return young; } + +pmd_t pmdp_invalidate_ad(struct vm_area_struct *vma, unsigned long address, + pmd_t *pmdp) +{ + /* + * No flush is necessary. Once an invalid PTE is established, the PTE's + * access and dirty bits cannot be updated. + */ + return pmdp_establish(vma, address, pmdp, pmd_mkinvalid(*pmdp)); +} #endif /** |