On Wed, 2017-05-31 at 06:58 -0700, Andy Lutomirski wrote:
> 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.
OK, fair enough.
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