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

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Message-ID: <CAFqt6zaFc_GenhfvsD0VPfepR-jjXypj+4CgNEuHMVq1WXV+8w@mail.gmail.com>
Date:   Fri, 5 Oct 2018 11:20:49 +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 Fri, Oct 5, 2018 at 1:16 AM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> Hi Souptick,
>
> On Thu, Oct 4, 2018 at 8:49 PM Souptick Joarder <jrdr.linux@...il.com> wrote:
> >
> > On Thu, Oct 4, 2018 at 11:47 PM Matthew Wilcox <willy@...radead.org> wrote:
> > >
> > > I think this is a bad plan.  What we should rather do is examine the current
> > > users of vm_insert_page() and ask "What interface would better replace
> > > vm_insert_page()?"
> > >
> > > As I've said to you before, I believe the right answer is to have a
> > > vm_insert_range() which takes an array of struct page pointers.  That
> > > fits the majority of remaining users.
> >
> > Ok, but it will take some time.
> > Is it a good idea to introduce the final vm_fault_t patch and then
> > start working on vm_insert_range as it will be bit time consuming ?
> >
>
> Well, why is there a rush? Development should be done in a patch
> series or a tree, and submitted as a whole, instead of sending partial
> patches.

Not in hurry, will do it in a patch series :-)
>
> Also, not sure if you saw my comments/review: if the interface is not
> going to change, why the name change? Why can't we simply keep using
> vm_insert_page?

yes, changing the name without changing the interface is a
bad approach and this can't be taken. As Matthew mentioned,
"vm_insert_range() which takes an array of struct page pointers.
That fits the majority of remaining users" would be a better approach
to fit this use case.

But yes, we can't keep vm_insert_page and vmf_insert_page together
as it doesn't guarantee  that future drivers will not use vm_insert_page
in #PF context ( which will generate new errno to VM_FAULT_CODE).

Any further comment form others on vm_Insert_range() approach ?