linux-kernel - Re: [PATCH 11/11] mm,sched: conditionally skip lazy TLB mm refcounting

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Message-ID: <1533317992.28585.103.camel@surriel.com>
Date:   Fri, 03 Aug 2018 13:39:52 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        luto@...nel.org, x86@...nel.org, efault@....de,
        dave.hansen@...el.com
Subject: Re: [PATCH 11/11] mm,sched: conditionally skip lazy TLB mm
 refcounting

On Fri, 2018-08-03 at 19:25 +0200, Peter Zijlstra wrote:
> On Fri, Aug 03, 2018 at 12:40:48PM -0400, Rik van Riel wrote:
> > On Fri, 2018-08-03 at 17:56 +0200, Peter Zijlstra wrote:
> > > 
> > > Why can't we skip the ->active_mm swizzle and keep ->active_mm ==
> > > ->mm.
> > > 
> > > Doing the swizzle but not the refcount just makes me itch.
> > 
> > I am working on that now, it adds another 7-8
> > patches on top of this series.
> 
> I thought those were taking ->active_mm out entirely, not avoiding
> the
> swizzle, but I might have missed something in the middle :-)

At this point, only the fact that ->active_mm is still
being used by a few places in the code :)

> > The big question is, do we want this optimization
> > to wait for further cleanups, or should we run with
> > code that seems to be stable right now, and put
> > additional cleanups and enhancements on top of it
> > later?
> 
> At the very least the Changelog needs to explain why we cannot do
> away
> with the swizzle now and how doing the swizzle without the
> refcounting
> is not completely broken (I think I see, but urgh).

The changelog for patches 9 & 10 explains, I think.

What is missing from my explanation?

How would you like to see it explained?

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