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

From: Christian König
Date: Fri Nov 20 2020 - 05:04:39 EST


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@xxxxxxxxxx>
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@xxxxxxxxxx>
Reviewed-by: Brian Paul <brianp@xxxxxxxxxx>

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@xxxxxxxxxx>
Cc: Brian Paul <brianp@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Christian Koenig <christian.koenig@xxxxxxx>
Cc: Huang Rui <ray.huang@xxxxxxx>

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.

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);