powerpc/mm: Don't send IPI to all cpus on THP updates

Now that we made sure that lockless walk of linux page table is mostly
limitted to current task(current->mm->pgdir) we can update the THP
update sequence to only send IPI to CPUs on which this task has run.
This helps in reducing the IPI overload on systems with large number
of CPUs.

WRT kvm even though kvm is walking page table with vpc->arch.pgdir,
it is done only on secondary CPUs and in that case we have primary CPU
added to task's mm cpumask. Sending an IPI to primary will force the
secondary to do a vm exit and hence this mm cpumask usage is safe
here.

WRT CAPI, we still end up walking linux page table with capi context
MM. For now the pte lookup serialization sends an IPI to all CPUs in
CPI is in use. We can further improve this by adding the CAPI
interrupt handling CPU to task mm cpumask. That will be done in a
later patch.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
index 5d8be076f8e5..1ee5452daf3a 100644
--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -811,7 +811,7 @@ pmd_t radix__pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long addre
 	pmd_clear(pmdp);
 
 	/*FIXME!!  Verify whether we need this kick below */
-	kick_all_cpus_sync();
+	serialize_against_pte_lookup(vma->vm_mm);
 
 	radix__flush_tlb_collapsed_pmd(vma->vm_mm, address);
 
@@ -873,16 +873,16 @@ pmd_t radix__pmdp_huge_get_and_clear(struct mm_struct *mm,
 	old = radix__pmd_hugepage_update(mm, addr, pmdp, ~0UL, 0);
 	old_pmd = __pmd(old);
 	/*
-	 * Serialize against find_linux_pte_or_hugepte which does lock-less
+	 * Serialize against find_current_mm_pte which does lock-less
 	 * lookup in page tables with local interrupts disabled. For huge pages
 	 * it casts pmd_t to pte_t. Since format of pte_t is different from
 	 * pmd_t we want to prevent transit from pmd pointing to page table
 	 * to pmd pointing to huge page (and back) while interrupts are disabled.
 	 * We clear pmd to possibly replace it with page table pointer in
 	 * different code paths. So make sure we wait for the parallel
-	 * find_linux_pte_or_hugepage to finish.
+	 * find_current_mm_pte to finish.
 	 */
-	kick_all_cpus_sync();
+	serialize_against_pte_lookup(mm);
 	return old_pmd;
 }