Re: [PATCH v6 3/3] drm/buddy: Add defragmentation support

[Christian König]

Am 16.02.24 um 13:23 schrieb Matthew Auld:

On 08/02/2024 15:50, Arunpravin Paneer Selvam wrote:

Add a function to support defragmentation.

v1: Defragment the memory beginning from min_order
     till the required memory space is available.

Signed-off-by: Arunpravin Paneer Selvam <arunpravin.paneersel...@amd.com>

Suggested-by: Matthew Auld <matthew.a...@intel.com>
---
  drivers/gpu/drm/drm_buddy.c | 67 +++++++++++++++++++++++++++++++------
  include/drm/drm_buddy.h     |  3 ++

No users?

Other question is how can a buddy allocator fragment in the first place?

Christian.

  2 files changed, 59 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index 33ad0cfbd54c..fac423d2cb73 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -276,10 +276,12 @@ drm_get_buddy(struct drm_buddy_block *block)
  }
  EXPORT_SYMBOL(drm_get_buddy);
  -static void __drm_buddy_free(struct drm_buddy *mm,
-                 struct drm_buddy_block *block)
+static unsigned int __drm_buddy_free(struct drm_buddy *mm,
+                     struct drm_buddy_block *block,
+                     bool defrag)
  {
      struct drm_buddy_block *parent;
+    unsigned int order;
        while ((parent = block->parent)) {
          struct drm_buddy_block *buddy;
@@ -289,12 +291,14 @@ static void __drm_buddy_free(struct drm_buddy *mm,
          if (!drm_buddy_block_is_free(buddy))
              break;
  -        if (drm_buddy_block_is_clear(block) !=
-            drm_buddy_block_is_clear(buddy))
-            break;
+        if (!defrag) {
+            if (drm_buddy_block_is_clear(block) !=
+                drm_buddy_block_is_clear(buddy))
+                break;
  -        if (drm_buddy_block_is_clear(block))
-            mark_cleared(parent);
+            if (drm_buddy_block_is_clear(block))
+                mark_cleared(parent);
+        }

Maybe check if the two blocks are incompatible and chuck a warn if they are not? Main thing is not to hide issues with split blocks that should have been merged before.

            list_del(&buddy->link);

  @@ -304,8 +308,49 @@ static void __drm_buddy_free(struct drm_buddy *mm,

          block = parent;
      }
  +    order = drm_buddy_block_order(block);
      mark_free(mm, block);
+
+    return order;
+}
+
+/**
+ * drm_buddy_defrag - Defragmentation routine
+ *
+ * @mm: DRM buddy manager
+ * @min_order: minimum order in the freelist to begin
+ * the defragmentation process
+ *
+ * Driver calls the defragmentation function when the
+ * requested memory allocation returns -ENOSPC.
+ */
+void drm_buddy_defrag(struct drm_buddy *mm,
+              unsigned int min_order)

Just wondering if we need "full defag" also? We would probably need to call this at fini() anyway.

+{
+    struct drm_buddy_block *block;
+    struct list_head *list;
+    unsigned int order;
+    int i;
+
+    if (min_order > mm->max_order)
+        return;
+
+    for (i = min_order - 1; i >= 0; i--) {

Need to be careful with min_order = 0 ?

+        list = &mm->free_list[i];
+        if (list_empty(list))
+            continue;
+
+        list_for_each_entry_reverse(block, list, link) {

Don't we need the safe_reverse() variant here, since this is removing from the list?

+            if (!block->parent)
+                continue;
+
+            order = __drm_buddy_free(mm, block, 1);
+            if (order >= min_order)
+                return;
+        }
+    }
  }
+EXPORT_SYMBOL(drm_buddy_defrag);
    /**
   * drm_buddy_free_block - free a block
@@ -321,7 +366,7 @@ void drm_buddy_free_block(struct drm_buddy *mm,
      if (drm_buddy_block_is_clear(block))
          mm->clear_avail += drm_buddy_block_size(mm, block);
  -    __drm_buddy_free(mm, block);
+    __drm_buddy_free(mm, block, 0);
  }
  EXPORT_SYMBOL(drm_buddy_free_block);
  @@ -470,7 +515,7 @@ __alloc_range_bias(struct drm_buddy *mm,
      if (buddy &&
          (drm_buddy_block_is_free(block) &&
           drm_buddy_block_is_free(buddy)))
-        __drm_buddy_free(mm, block);
+        __drm_buddy_free(mm, block, 0);
      return ERR_PTR(err);
  }
  @@ -588,7 +633,7 @@ alloc_from_freelist(struct drm_buddy *mm,
    err_undo:
      if (tmp != order)
-        __drm_buddy_free(mm, block);
+        __drm_buddy_free(mm, block, 0);
      return ERR_PTR(err);
  }
  @@ -668,7 +713,7 @@ static int __alloc_range(struct drm_buddy *mm,
      if (buddy &&
          (drm_buddy_block_is_free(block) &&
           drm_buddy_block_is_free(buddy)))
-        __drm_buddy_free(mm, block);
+        __drm_buddy_free(mm, block, 0);
    err_free:
      if (err == -ENOSPC && total_allocated_on_err) {
diff --git a/include/drm/drm_buddy.h b/include/drm/drm_buddy.h
index d81c596dfa38..d0f63e7b5915 100644
--- a/include/drm/drm_buddy.h
+++ b/include/drm/drm_buddy.h
@@ -166,6 +166,9 @@ void drm_buddy_free_list(struct drm_buddy *mm,
               struct list_head *objects,
               unsigned int flags);
  +void drm_buddy_defrag(struct drm_buddy *mm,
+              unsigned int min_order);
+
  void drm_buddy_print(struct drm_buddy *mm, struct drm_printer *p);
  void drm_buddy_block_print(struct drm_buddy *mm,
                 struct drm_buddy_block *block,