linux-kernel - Re: [PATCH v2] mm: Introduce new function vm_insert_kmem

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Date:   Tue, 23 Oct 2018 17:44:32 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        robin@...tonic.nl, stefanr@...6.in-berlin.de, hjc@...k-chips.com,
        Heiko Stuebner <heiko@...ech.de>, airlied@...ux.ie,
        robin.murphy@....com, iamjoonsoo.kim@....com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kees Cook <keescook@...omium.org>, treding@...dia.com,
        Michal Hocko <mhocko@...e.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>, aryabinin@...tuozzo.com,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kate Stewart <kstewart@...uxfoundation.org>, tchibo@...gle.com,
        riel@...hat.com, Minchan Kim <minchan@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Huang, Ying" <ying.huang@...el.com>, ak@...ux.intel.com,
        rppt@...ux.vnet.ibm.com, linux@...inikbrodowski.net,
        Arnd Bergmann <arnd@...db.de>, cpandya@...eaurora.org,
        hannes@...xchg.org, Joe Perches <joe@...ches.com>,
        mcgrof@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        linux1394-devel@...ts.sourceforge.net,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2] mm: Introduce new function vm_insert_kmem_page

On Sat, Oct 6, 2018 at 4:19 PM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> On Sat, Oct 6, 2018 at 7:11 AM Souptick Joarder <jrdr.linux@...il.com> wrote:
> >
> > On Fri, Oct 5, 2018 at 11:39 PM Miguel Ojeda
> > <miguel.ojeda.sandonis@...il.com> wrote:
> > > They are not supposed to be "steps". You did it with 70+ commits (!!)
> > > over the course of several months. Why a tree wasn't created, stuff
> > > developed there, and when done, submitted it for review?
> >
> > Because we already have a plan for entire vm_fault_t migration and
> > the * instruction * was to send one patch per driver.
>
> The instruction?

Sorry for the delayed response.
Instruction from Matthew  Wilcox who is supervising the entire vm_fault_t
migration work :-)

>
> > >
> > > Fine, but you haven't answered to the other parts of my email: you
> > > don't explain why you choose one alternative over the others, you
> > > simply keep changing the approach.
> >
> > We are going in circles here. That you want to convert vm_insert_page
> > to vmf_insert_page for the PF case is fine and understood. However,
> > you don't *need* to introduce a new name for the remaining non-PF
> > cases if the function is going to be the exact same thing as before.
> > You say "The final goal is to remove vm_insert_page", but you haven't
> > justified *why* you need to remove that name.
> >
> > I think I have given that answer. If we don't remove vm_insert_page,
> > future #PF caller will have option to use it. But those should be
> > restricted. How are we going to restrict vm_insert_page in one half
> > of kernel when other half is still using it  ?? Is there any way ? ( I don't
> > know)
>
> Ah, so that is what you are concerned about: future misuses. Well, I
> don't really see the problem. There are only ~18 calls to
> vm_insert_page() in the entire kernel: checking if people is using it
> properly for a while should be easy. As long as the new behavior is
> documented properly, it should be fine. If you are really concerned
> about mistakes being made, then fine, we can rename it as I suggested.
>
> Now, the new vm_insert_range() is another topic. It simplifies a few
> of the callers and buys us the rename at the same time, so I am also
> OK with it.
>
> As you see, I am not against the changes -- it is just that they
> should clearly justified. :-) It wasn't clear what your problem with
> the current vm_insert_page() is.
>
> Cheers,
> Miguel