On Thu, May 30, 2019 at 12:56 AM Zhenzhong Duan
<[email protected]> wrote:
>
> This is a small optimization to stale TLB flush, if there is one new TLB
> flush, let it choose to do partial or full flush. or else, the stale
> flush take over and do full flush.
I think this is invalid because:
>
> + if (unlikely(f->new_tlb_gen <= local_tlb_gen &&
> + local_tlb_gen + 1 == mm_tlb_gen)) {
> + /*
> + * For stale TLB flush request, if there will be one new TLB
> + * flush coming, we leave the work to the new IPI as it knows
> + * partial or full TLB flush to take, or else we do the full
> + * flush.
> + */
> + trace_tlb_flush(reason, 0);
> + return;
We do indeed know that the TLB will get flushed eventually, but we're
actually providing a stronger guarantee that the TLB will be
adequately flushed by the time we return. Otherwise, after
flush_tlb_mm_range(), there will be a window in which the TLB isn't
flushed yet.
