linux-kernel - Re: [PATCH v3 0/4] shoot lazy tlbs

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Date:   Sat, 05 Jun 2021 10:17:50 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Anton Blanchard <anton@...abs.org>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v3 0/4] shoot lazy tlbs

Excerpts from Andy Lutomirski's message of June 5, 2021 3:05 am:
> On 6/4/21 9:54 AM, Andy Lutomirski wrote:
>> On 5/31/21 11:22 PM, Nicholas Piggin wrote:
>>> There haven't been objections to the series since last posting, this
>>> is just a rebase and tidies up a few comments minor patch rearranging.
>>>
>> 
>> I continue to object to having too many modes.  I like my more generic
>> improvements better.  Let me try to find some time to email again.
>> 
> 
> Specifically, this:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/mm

That's worse than what powerpc does with the shoot lazies code so 
we wouldn't use it anyway.

The fact is mm-cpumask and lazy mm is very architecture specific, so I 
don't really see that another "mode" is such a problem, it's for the 
most part "this is what powerpc does" -> "this is what powerpc does".
The only mode in the context switch is just "take a ref on the lazy mm"
or "don't take a ref". Surely that's not too onerous to add!?

Actually the bigger part of it is actually the no-lazy mmu mode which
is not yet used, I thought it was a neat little demonstrator of how code
works with/without lazy but I will get rid of that for submission.

> I, or someone, needs to dust off my membarrier series before any of
> these kinds of changes get made.  The barrier situation in the scheduler
> is too confusing otherwise.
> 

I disagree, I've disentangled the changes from membarrier stuff now, 
they can be done concurrently.

Thanks,
Nick