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

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Date:   Fri, 5 Oct 2018 15:31:42 +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 2:22 PM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> Hi Souptick,
>
> On Fri, Oct 5, 2018 at 7:51 AM Souptick Joarder <jrdr.linux@...il.com> wrote:
> >
> > On Fri, Oct 5, 2018 at 1:16 AM Miguel Ojeda
> > <miguel.ojeda.sandonis@...il.com> wrote:
> > >
> > >
> > > 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).
> >
>
> Maybe I am hard of thinking, but aren't you planning to remove
> vm_insert_page with these changes? If yes, why you can't use the keep
> vm_insert_page name? In other words, keep returning what the drivers
> expect?

The final goal is to remove vm_insert_page by converting it to
vmf_insert_page. But to do that we have to first introduce the
new API which is similar to vm_insert_page  (for non #PF). I tried this by
introducing vm_insert_kmem_page ( * identical as vm_insert_page
except API name *) in this patch. But this looks like a bad approach.

The new proposal is to introduce vm_insert_range() ( * which might be
bit different from vm_insert_page but will serve all the non #PF use cases)