Re: [PATCH v2 0/5] mm/mprotect: avoid unnecessary TLB flushes

Andrew Morton
2021-10-22T03:04:55Z

On Thu, 21 Oct 2021 05:21:07 -0700 Nadav Amit <nadav.amit@gmail.com> wrote:

> This patch-set is intended to remove unnecessary TLB flushes. It is
> based on feedback from v1 and several bugs I found in v1 myself.
>
> Basically, there are 3 optimizations in this patch-set:
> 1. Avoiding TLB flushes on change_huge_pmd() that are only needed to
> prevent the A/D bits from changing.
> 2. Use TLB batching infrastructure to batch flushes across VMAs and
> do better/fewer flushes.
> 3. Avoid TLB flushes on permission demotion.
>
> Andrea asked for the aforementioned (2) to come after (3), but this
> is not simple (specifically since change_prot_numa() needs the number
> of pages affected).

[1/5] appears to be a significant fix which should probably be
backported into -stable kernels. If you agree with this then I suggest
it be prepared as a standalone patch, separate from the other four
patches. With a cc:stable.

And the remaining patches are a performance optimization. Has any
attempt been made to quantify the benefits?