Re: [RFC 03/10] x86/mm: Make the batched unmap TLB flush API more generic

Andy Lutomirski
2017-05-09T13:03:18Z

On Mon, May 8, 2017 at 8:34 AM, Dave Hansen <dave.hansen@intel.com> wrote:
> On 05/07/2017 05:38 AM, Andy Lutomirski wrote:
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index f6838015810f..2e568c82f477 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -579,25 +579,12 @@ void page_unlock_anon_vma_read(struct anon_vma *anon_vma)
>> void try_to_unmap_flush(void)
>> {
>> struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
>> - int cpu;
>>
>> if (!tlb_ubc->flush_required)
>> return;
>>
>> - cpu = get_cpu();
>> -
>> - if (cpumask_test_cpu(cpu, &tlb_ubc->cpumask)) {
>> - count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
>> - local_flush_tlb();
>> - trace_tlb_flush(TLB_LOCAL_SHOOTDOWN, TLB_FLUSH_ALL);
>> - }
>> -
>> - if (cpumask_any_but(&tlb_ubc->cpumask, cpu) < nr_cpu_ids)
>> - flush_tlb_others(&tlb_ubc->cpumask, NULL, 0, TLB_FLUSH_ALL);
>> - cpumask_clear(&tlb_ubc->cpumask);
>> tlb_ubc->flush_required = false;
>> tlb_ubc->writable = false;
>> - put_cpu();
>> }
>>
>> /* Flush iff there are potentially writable TLB entries that can race with IO */
>> @@ -613,7 +600,7 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
>> {
>> struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
>>
>> - cpumask_or(&tlb_ubc->cpumask, &tlb_ubc->cpumask, mm_cpumask(mm));
>> + arch_tlbbatch_add_mm(&tlb_ubc->arch, mm);
>> tlb_ubc->flush_required = true;
>>
>> /*
>
> Looking at this patch in isolation, how can this be safe? It removes
> TLB flushes from the generic code. Do other patches in the series fix
> this up?

Hmm? Unless I totally screwed this up, this patch just moves the
flushes around -- it shouldn't remove any flushes.