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authorNadav Amit <namit@vmware.com>2022-05-09 18:20:50 -0700
committerAndrew Morton <akpm@linux-foundation.org>2022-05-13 07:20:05 -0700
commit4f83145721f362c2f4d312edc4755269a2069488 (patch)
tree4a13cb87519b0bd3659d91f6f3a19df4575d4f96 /mm/pgtable-generic.c
parentc9fe66560bf2dc7d109754414e309888cb8c9ba9 (diff)
downloadlwn-4f83145721f362c2f4d312edc4755269a2069488.tar.gz
lwn-4f83145721f362c2f4d312edc4755269a2069488.zip
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/20220401180821.1986781-4-namit@vmware.com Signed-off-by: Nadav Amit <namit@vmware.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Cooper <andrew.cooper3@citrix.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Peter Xu <peterx@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will@kernel.org> Cc: Yu Zhao <yuzhao@google.com> Cc: Nick Piggin <npiggin@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/pgtable-generic.c')
-rw-r--r--mm/pgtable-generic.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index 6523fda274e5..90ab721a12a8 100644
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -201,6 +201,14 @@ pmd_t pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
}
#endif
+#ifndef __HAVE_ARCH_PMDP_INVALIDATE_AD
+pmd_t pmdp_invalidate_ad(struct vm_area_struct *vma, unsigned long address,
+ pmd_t *pmdp)
+{
+ return pmdp_invalidate(vma, address, pmdp);
+}
+#endif
+
#ifndef pmdp_collapse_flush
pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
pmd_t *pmdp)