diff mbox

[v2,1/5] drm/gem: replace misleading comment

Message ID 1401021252-29006-1-git-send-email-dh.herrmann@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

David Herrmann May 25, 2014, 12:34 p.m. UTC 
shmem supports page-relocations during swapin since quite some time. It
was implemented in:

    commit bde05d1ccd512696b09db9dd2e5f33ad19152605
    Author: Hugh Dickins <hughd@google.com>
    Date:   Tue May 29 15:06:38 2012 -0700

        shmem: replace page if mapping excludes its zone

The gem-comment about wrongly placed DMA32 pages is no longer valid.
Replace it with a proper comment but keep the BUG_ON() to verify correct
shmem behavior.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
---
 drivers/gpu/drm/drm_gem.c | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

Comments

Daniel Vetter May 25, 2014, 9:53 p.m. UTC | #1 
On Sun, May 25, 2014 at 2:34 PM, David Herrmann <dh.herrmann@gmail.com> wrote:
> shmem supports page-relocations during swapin since quite some time. It
> was implemented in:
>
>     commit bde05d1ccd512696b09db9dd2e5f33ad19152605
>     Author: Hugh Dickins <hughd@google.com>
>     Date:   Tue May 29 15:06:38 2012 -0700
>
>         shmem: replace page if mapping excludes its zone
>
> The gem-comment about wrongly placed DMA32 pages is no longer valid.
> Replace it with a proper comment but keep the BUG_ON() to verify correct
> shmem behavior.
>
> Signed-off-by: David Herrmann <dh.herrmann@gmail.com>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff mbox

Patch

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 9909bef..f7d7119 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -474,21 +474,10 @@  struct page **drm_gem_get_pages(struct drm_gem_object *obj, gfp_t gfpmask)
 			goto fail;
 		pages[i] = p;
 
-		/* There is a hypothetical issue w/ drivers that require
-		 * buffer memory in the low 4GB.. if the pages are un-
-		 * pinned, and swapped out, they can end up swapped back
-		 * in above 4GB.  If pages are already in memory, then
-		 * shmem_read_mapping_page_gfp will ignore the gfpmask,
-		 * even if the already in-memory page disobeys the mask.
-		 *
-		 * It is only a theoretical issue today, because none of
-		 * the devices with this limitation can be populated with
-		 * enough memory to trigger the issue.  But this BUG_ON()
-		 * is here as a reminder in case the problem with
-		 * shmem_read_mapping_page_gfp() isn't solved by the time
-		 * it does become a real issue.
-		 *
-		 * See this thread: http://lkml.org/lkml/2011/7/11/238
+		/* Make sure shmem keeps __GFP_DMA32 allocated pages in the
+		 * correct region during swapin. Note that this requires
+		 * __GFP_DMA32 to be set in mapping_gfp_mask(inode->i_mapping)
+		 * so shmem can relocate pages during swapin if required.
 		 */
 		BUG_ON((gfpmask & __GFP_DMA32) &&
 				(page_to_pfn(p) >= 0x00100000UL));