linux-kernel - Re: [RFC PATCH 02/14] sparc64: add new fields to mmu context for shared context support

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Message-ID: <20161217073406.GA23567@ravnborg.org>
Date:   Sat, 17 Dec 2016 08:34:06 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     sparclinux@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        Bob Picco <bob.picco@...cle.com>,
        Nitin Gupta <nitin.m.gupta@...cle.com>,
        Vijay Kumar <vijay.ac.kumar@...cle.com>,
        Julian Calaby <julian.calaby@...il.com>,
        Adam Buchbinder <adam.buchbinder@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 02/14] sparc64: add new fields to mmu context for
 shared context support

Hi Mike.

On Fri, Dec 16, 2016 at 10:35:25AM -0800, Mike Kravetz wrote:
> Add new fields to the mm_context structure to support shared context.
> Instead of a simple context ID, add a pointer to a structure with a
> reference count.  This is needed as multiple tasks will share the
> context ID.

What are the benefits with the shared_mmu_ctx struct?
It does not save any space in mm_context_t, and the CPU only
supports one extra context.
So it looks like over-engineering with all the extra administration
required to handle it with refcount, poitners etc.

what do I miss?

	Sam