On Mon, May 29, 2017 at 4:42 PM, Rik van Riel <riel@xxxxxxxxxx> wrote:
> On Sun, 2017-05-28 at 10:00 -0700, Andy Lutomirski wrote:
>
>> @@ -292,61 +303,33 @@ static unsigned long
>> tlb_single_page_flush_ceiling __read_mostly = 33;
>> void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
>> unsigned long end, unsigned long
>> vmflag)
>> {
>> - unsigned long addr;
>> - struct flush_tlb_info info;
>> - /* do a global flush by default */
>> - unsigned long base_pages_to_flush = TLB_FLUSH_ALL;
>> -
>> - preempt_disable();
>> + int cpu;
>>
>> - if ((end != TLB_FLUSH_ALL) && !(vmflag & VM_HUGETLB))
>> - base_pages_to_flush = (end - start) >> PAGE_SHIFT;
>> - if (base_pages_to_flush > tlb_single_page_flush_ceiling)
>> - base_pages_to_flush = TLB_FLUSH_ALL;
>> -
>> - if (current->active_mm != mm) {
>> - /* Synchronize with switch_mm. */
>> - smp_mb();
>> -
>> - goto out;
>> - }
>> -
>> - if (this_cpu_read(cpu_tlbstate.state) != TLBSTATE_OK) {
>> - leave_mm(smp_processor_id());
>> + struct flush_tlb_info info = {
>> + .mm = mm,
>> + };
>>
>> - /* Synchronize with switch_mm. */
>> - smp_mb();
>> + cpu = get_cpu();
>>
>> - goto out;
>> - }
>> + /* Synchronize with switch_mm. */
>> + smp_mb();
>>
>> - /*
>> - * Both branches below are implicit full barriers (MOV to CR
>> or
>> - * INVLPG) that synchronize with switch_mm.
>> - */
>> - if (base_pages_to_flush == TLB_FLUSH_ALL) {
>> - count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
>> - local_flush_tlb();
>> + /* Should we flush just the requested range? */
>> + if ((end != TLB_FLUSH_ALL) &&
>> + !(vmflag & VM_HUGETLB) &&
>> + ((end - start) >> PAGE_SHIFT) <=
>> tlb_single_page_flush_ceiling) {
>> + info.start = start;
>> + info.end = end;
>> } else {
>> - /* flush range by one by one 'invlpg' */
>> - for (addr = start; addr < end; addr +=
>> PAGE_SIZE) {
>> - count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE);
>> - __flush_tlb_single(addr);
>> - }
>> - }
>> - trace_tlb_flush(TLB_LOCAL_MM_SHOOTDOWN,
>> base_pages_to_flush);
>> -out:
>> - info.mm = mm;
>> - if (base_pages_to_flush == TLB_FLUSH_ALL) {
>> info.start = 0UL;
>> info.end = TLB_FLUSH_ALL;
>> - } else {
>> - info.start = start;
>> - info.end = end;
>> }
>> - if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) <
>> nr_cpu_ids)
>> +
>> + if (mm == current->active_mm)
>> + flush_tlb_func_local(&info, TLB_LOCAL_MM_SHOOTDOWN);
>
> It looks like this could cause flush_tlb_func_local to be
> called over and over again even while cpu_tlbstate.state
> equals TLBSTATE_LAZY, because active_mm is not changed by
> leave_mm.
>
> Do you want to also test cpu_tlbstate.state != TLBSTATE_OK
> here, to ensure flush_tlb_func_local is only called when
> necessary?
>
I don't think that would buy us much. func_tlb_flush_local will be
called, but it will call flush_tlb_func_common(), which will notice
that we're lazy and call leave_mm() instead of flushing. leave_mm()
won't do anything if we're already using init_mm. The overall effect
should be the same as it was before this patch, although it's a bit
more indirect with the patch applied.
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