[PATCH v4 32/38] drm: Simplify drm_mm scan-list manipulation

Chris Wilson
2016-12-22T08:36:35Z

Since we mandate a strict reverse-order of drm_mm_scan_remove_block()
after drm_mm_scan_add_block() we can further simplify the list
manipulations when generating the temporary scan-hole.

v2: Highlight the games being played with the lists to track the scan
holes without allocation.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
drivers/gpu/drm/drm_mm.c | 35 ++++++++++++++++++-----------------
include/drm/drm_mm.h | 7 +------
2 files changed, 19 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 0441d84fba74..ccca8dafb7fc 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -518,9 +518,7 @@ void drm_mm_remove_node(struct drm_mm_node *node)
struct drm_mm_node *prev_node;

DRM_MM_BUG_ON(!node->allocated);
- DRM_MM_BUG_ON(node->scanned_block ||
- node->scanned_prev_free ||
- node->scanned_next_free);
+ DRM_MM_BUG_ON(node->scanned_block);

prev_node =
list_entry(node->node_list.prev, struct drm_mm_node, node_list);
@@ -757,8 +755,6 @@ void drm_mm_scan_init_with_range(struct drm_mm_scan *scan,

scan->hit_start = U64_MAX;
scan->hit_end = 0;
-
- scan->prev_scanned_node = NULL;
}
EXPORT_SYMBOL(drm_mm_scan_init_with_range);

@@ -787,14 +783,14 @@ bool drm_mm_scan_add_block(struct drm_mm_scan *scan,
node->scanned_block = true;
mm->scan_active++;

+ /* Remove this block from the node_list so that we enlarge the hole
+ * (distance between the end of our previous node and the start of
+ * or next), without poisoning the link so that we can restore it
+ * later in drm_mm_scan_remove_block().
+ */
hole = list_prev_entry(node, node_list);
-
- node->scanned_preceeds_hole = hole->hole_follows;
- hole->hole_follows = 1;
- list_del(&node->node_list);
- node->node_list.prev = &hole->node_list;
- node->node_list.next = &scan->prev_scanned_node->node_list;
- scan->prev_scanned_node = node;
+ DRM_MM_BUG_ON(list_next_entry(hole, node_list) != node);
+ __list_del_entry(&node->node_list);

hole_start = __drm_mm_hole_node_start(hole);
hole_end = __drm_mm_hole_node_end(hole);
@@ -888,9 +884,17 @@ bool drm_mm_scan_remove_block(struct drm_mm_scan *scan,
DRM_MM_BUG_ON(!node->mm->scan_active);
node->mm->scan_active--;

+ /* During drm_mm_scan_add_block() we decoupled this node leaving
+ * its pointers intact. Now that the caller is walking back along
+ * the eviction list we can restore this block into its rightful
+ * place on the full node_list. To confirm that the caller is walking
+ * backwards correctly we check that prev_node->next == node->next,
+ * i.e. both believe the same node should be on the other side of the
+ * hole.
+ */
prev_node = list_prev_entry(node, node_list);
-
- prev_node->hole_follows = node->scanned_preceeds_hole;
+ DRM_MM_BUG_ON(list_next_entry(prev_node, node_list) !=
+ list_next_entry(node, node_list));
list_add(&node->node_list, &prev_node->node_list);

return (node->start + node->size > scan->hit_start &&
@@ -917,9 +921,6 @@ void drm_mm_init(struct drm_mm *mm, u64 start, u64 size)
INIT_LIST_HEAD(&mm->head_node.node_list);
mm->head_node.allocated = 0;
mm->head_node.hole_follows = 1;
- mm->head_node.scanned_block = 0;
- mm->head_node.scanned_prev_free = 0;
- mm->head_node.scanned_next_free = 0;
mm->head_node.mm = mm;
mm->head_node.start = start + size;
mm->head_node.size = start - mm->head_node.start;
diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
index d6701d56ea74..ff120b7d0f85 100644
--- a/include/drm/drm_mm.h
+++ b/include/drm/drm_mm.h
@@ -74,11 +74,8 @@ struct drm_mm_node {
struct list_head hole_stack;
struct rb_node rb;
unsigned hole_follows : 1;
- unsigned scanned_block : 1;
- unsigned scanned_prev_free : 1;
- unsigned scanned_next_free : 1;
- unsigned scanned_preceeds_hole : 1;
unsigned allocated : 1;
+ bool scanned_block : 1;
unsigned long color;
u64 start;
u64 size;
@@ -118,8 +115,6 @@ struct drm_mm_scan {
u64 hit_start;
u64 hit_end;

- struct drm_mm_node *prev_scanned_node;
-
unsigned long color;
unsigned int flags;
};