On Mon, 29 Jul 2019 17:20:52 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote:
> > > @@ -1022,7 +1023,16 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
> > > flush_tlb_batched_pending(mm);
> > > arch_enter_lazy_mmu_mode();
> > > do {
> > > - pte_t ptent = *pte;
> > > + pte_t ptent;
> > > +
> > > + if (progress >= 32) {
> > > + progress = 0;
> > > + if (need_resched())
> > > + break;
> > > + }
> > > + progress += 8;
> >
> > Why 8?
>
> Just copied from copy_pte_range.
copy_pte_range() does
if (pte_none(*src_pte)) {
progress++;
continue;
}
entry.val = copy_one_pte(dst_mm, src_mm, dst_pte, src_pte,
vma, addr, rss);
if (entry.val)
break;
progress += 8;
which appears to be an attempt to balance the cost of copy_one_pte()
against the cost of not calling copy_one_pte().
Your code doesn't do this balancing and hence can be simpler.
It all seems a bit overdesigned. need_resched() is cheap. It's
possibly a mistake to check need_resched() on *every* loop because some
crazy scheduling load might livelock us. But surely it would be enough
to do something like
if (progress++ && need_resched()) {
<reschedule>
progress = 0;
}
and leave it at that?
