linux-kernel - Re: [PATCH] drm/ttm: don't set page->mapping

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Message-ID: <CAKMK7uHnYGiBsBLeyGA8sZXmAiaHaym9jnLKN_xY4VAtKJjG5A@mail.gmail.com>
Date:   Fri, 20 Nov 2020 11:05:50 +0100
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     Christian König <christian.koenig@....com>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Linux MM <linux-mm@...ck.org>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Brian Paul <brianp@...are.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Huang Rui <ray.huang@....com>
Subject: Re: [PATCH] drm/ttm: don't set page->mapping

On Fri, Nov 20, 2020 at 11:04 AM Christian König
<christian.koenig@....com> wrote:
>
> Am 20.11.20 um 10:54 schrieb Daniel Vetter:
> > Random observation while trying to review Christian's patch series to
> > stop looking at struct page for dma-buf imports.
> >
> > This was originally added in
> >
> > commit 58aa6622d32af7d2c08d45085f44c54554a16ed7
> > Author: Thomas Hellstrom <thellstrom@...are.com>
> > Date:   Fri Jan 3 11:47:23 2014 +0100
> >
> >      drm/ttm: Correctly set page mapping and -index members
> >
> >      Needed for some vm operations; most notably unmap_mapping_range() with
> >      even_cows = 0.
> >
> >      Signed-off-by: Thomas Hellstrom <thellstrom@...are.com>
> >      Reviewed-by: Brian Paul <brianp@...are.com>
> >
> > but we do not have a single caller of unmap_mapping_range with
> > even_cows == 0. And all the gem drivers don't do this, so another
> > small thing we could standardize between drm and ttm drivers.
> >
> > Plus I don't really see a need for unamp_mapping_range where we don't
> > want to indiscriminately shoot down all ptes.
> >
> > Cc: Thomas Hellstrom <thellstrom@...are.com>
> > Cc: Brian Paul <brianp@...are.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
> > Cc: Christian Koenig <christian.koenig@....com>
> > Cc: Huang Rui <ray.huang@....com>
>
> This is still a NAK as long as we can't come up with a better way to
> track TTMs page allocations.
>
> Additional to that page_mapping() is used quite extensively in the mm
> code and I'm not sure if that isn't needed for other stuff as well.

Apologies, I'm honestly not quite sure how this lone patch here ended
up in this submission. I didn't want to send it out.
-Daniel

>
> Regards,
> Christian.
>
> > ---
> >   drivers/gpu/drm/ttm/ttm_tt.c | 12 ------------
> >   1 file changed, 12 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> > index da9eeffe0c6d..5b2eb6d58bb7 100644
> > --- a/drivers/gpu/drm/ttm/ttm_tt.c
> > +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> > @@ -284,17 +284,6 @@ int ttm_tt_swapout(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
> >       return ret;
> >   }
> >
> > -static void ttm_tt_add_mapping(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
> > -{
> > -     pgoff_t i;
> > -
> > -     if (ttm->page_flags & TTM_PAGE_FLAG_SG)
> > -             return;
> > -
> > -     for (i = 0; i < ttm->num_pages; ++i)
> > -             ttm->pages[i]->mapping = bdev->dev_mapping;
> > -}
> > -
> >   int ttm_tt_populate(struct ttm_bo_device *bdev,
> >                   struct ttm_tt *ttm, struct ttm_operation_ctx *ctx)
> >   {
> > @@ -313,7 +302,6 @@ int ttm_tt_populate(struct ttm_bo_device *bdev,
> >       if (ret)
> >               return ret;
> >
> > -     ttm_tt_add_mapping(bdev, ttm);
> >       ttm->page_flags |= TTM_PAGE_FLAG_PRIV_POPULATED;
> >       if (unlikely(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
> >               ret = ttm_tt_swapin(ttm);
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch