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

Dave Hansen
2017-05-09T17:13:28Z

On 05/09/2017 06:02 AM, Andy Lutomirski wrote:
> 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.

This takes a flush out of try_to_unmap_flush(). It adds code for
arch_tlbbatch_flush(), but not *calls* to arch_tlbbatch_flush() that I
can see.

I actually don't see _any_ in the whole series in a quick grepping. Am
I just missing them?