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Commit 2123000b authored by David Herrmann's avatar David Herrmann Committed by Dave Airlie
Browse files

drm/gem: replace misleading comment 



shmem supports page-relocations during swapin since quite some time. It
was implemented in:

    commit bde05d1c
    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The gem-comment about wrongly placed DMA32 pages is no longer valid.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: default avatarDavid Herrmann <dh.herrmann@gmail.com>
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent 89086bca

drivers/gpu/drm/drm_gem.c

+4 −15
Original line number Diff line number Diff line
@@ -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));