Re: [tip:x86/mm] x86/mm: Avoid superflous leave_mm() in the TLB flush path

[Linus Torvalds]

On Mon, Dec 5, 2011 at 9:56 AM, tip-bot for Shaohua Li
<shaohua.li@xxxxxxxxx> wrote:
>
> x86/mm: Avoid superflous leave_mm() in the TLB flush path
>
> If just one page VA tlb is required to be flushed and current
> task is in lazy TLB state, doing leave_mm() is superfluous
> because it flushes the whole TLB.  This can reduce some TLB
> miss.

Are you sure this is a good idea?

We may be *much* better off leaving the VM and avoiding future IPI's
than trying to flush pages one by one over and over again.

IPI's are expensive.

I don't think you thought this through, and if you *did* think it
through and actually have numbers that it's cheaper to stay with the
MM, I think you need to show those numbers.

                     Linus
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