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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 6 Aug 2019 11:50:42 -0700
Message-ID: <CAHk-=wi7L0MDG7DY39Hx6v8jUMSq3ZCE3QTnKKirba_8KAFNyw@mail.gmail.com>
Subject: Re: drm pull for v5.3-rc1
To:     Christoph Hellwig <hch@infradead.org>
Cc:     =?UTF-8?Q?Thomas_Hellstr=C3=B6m_=28VMware=29?= 
        <thomas@shipmail.org>, Dave Airlie <airlied@gmail.com>,
        Thomas Hellstrom <thellstrom@vmware.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        LKML <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Jerome Glisse <jglisse@redhat.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Steven Price <steven.price@arm.com>,
        Linux-MM <linux-mm@kvack.org>
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On Tue, Aug 6, 2019 at 12:38 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> Seems like no one took this up.  Below is a version which I think is
> slightly better by also moving the mm_walk structure initialization
> into the helpers, with an outcome of just a handful of added lines.

Ack. Agreed, I think that's a nicer interface.

In fact, I do note that a lot of the users don't actually use the
"void *private" argument at all - they just want the walker - and just
pass in a NULL private pointer. So we have things like this:

> +       if (walk_page_range(&init_mm, va, va + size, &set_nocache_walk_ops,
> +                       NULL)) {

and in a perfect world we'd have arguments with default values so that
we could skip those entirely for when people just don't need it.

I'm not a huge fan of C++ because of a lot of the complexity (and some
really bad decisions), but many of the _syntactic_ things in C++ would
be nice to use. This one doesn't seem to be one that the gcc people
have picked up as an extension ;(

Yes, yes, we could do it with a macro, I guess.

   #define walk_page_range(mm, start,end, ops, ...) \
       __walk_page_range(mm, start, end, (NULL , ## __VA_ARGS__))

but I'm not sure it's worthwhile.

                  Linus