linux-kernel - [PATCH] drm/gem: remove obsolete BUG

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Message-Id: <1400674586-17968-1-git-send-email-dh.herrmann@gmail.com>
Date:	Wed, 21 May 2014 14:16:26 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	dri-devel@...ts.freedesktop.org
Cc:	robdclark@...il.com, airlied@...il.com, daniel.vetter@...ll.ch,
	hughd@...gle.com, linux-kernel@...r.kernel.org,
	David Herrmann <dh.herrmann@...il.com>
Subject: [PATCH] drm/gem: remove obsolete BUG_ON

The shmem subsystem supports relocating pages on swap-in in case it was
loaded into the wrong zone. This was implemented 2 years ago in:

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

        shmem: replace page if mapping excludes its zone

If a driver requires pages to be in a specific zone, they _must_ set the
correct GFP flags (like __GFP_DMA32) in mapping_gfp_mask(mapping). shmem
will make sure that any page leaving the swap-cache is located in a
compatible zone.

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

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 9909bef..a6146ab 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -473,25 +473,6 @@ struct page **drm_gem_get_pages(struct drm_gem_object *obj, gfp_t gfpmask)
 		if (IS_ERR(p))
 			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
-		 */
-		BUG_ON((gfpmask & __GFP_DMA32) &&
-				(page_to_pfn(p) >= 0x00100000UL));
 	}
 
 	return pages;
-- 
1.9.3

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