Re: [PATCH v4] drm: Optimise for continuous memory allocation

From: Christian König
Date: Tue Nov 29 2022 - 06:32:44 EST

Am 29.11.22 um 11:56 schrieb xinhui pan:
Currently drm-buddy does not have full knowledge of continuous memory.

Lets consider scenario below.
order 1: L R
order 0: LL LR RL RR
for order 1 allocation, it can offer L or R or LR+RL.

For now, we only implement L or R case for continuous memory allocation.
So this patch aims to implement the rest cases.

Adding a new member leaf_link which links all leaf blocks in asceding
order. Now we can find more than 2 sub-order blocks easier.
Say, order 4 can be combined with corresponding order 4, 2+2, 1+2+1,
0+1+2+0, 0+2+1+0.

Well that description is a bit confusing and doesn't make to much sense to me.

When you have two adjacent free order 0 blocks then those should be automatically combined into an order 1. This is a fundamental property of the buddy allocator, otherwise the whole algorithm won't work.

When you have the case of a free order 1 block with two adjacent free order 0 blocks then we a fragmented address space. In this case the best approach is to fail the allocation and start to swap things out.

So what exactly is the goal here?

Regards,
Christian.


Signed-off-by: xinhui pan <xinhui.pan@xxxxxxx>
---
change from v3:
reworked totally. adding leaf_link.

change from v2:
search continuous block in nearby root if needed

change from v1:
implement top-down continuous allocation
---
drivers/gpu/drm/drm_buddy.c | 108 +++++++++++++++++++++++++++++++++---
include/drm/drm_buddy.h | 1 +
2 files changed, 102 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index 11bb59399471..8edafb99b02c 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -80,6 +80,7 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
{
unsigned int i;
u64 offset;
+ LIST_HEAD(leaf);
if (size < chunk_size)
return -EINVAL;
@@ -136,6 +137,7 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
goto out_free_roots;
mark_free(mm, root);
+ list_add_tail(&root->leaf_link, &leaf);
BUG_ON(i > mm->max_order);
BUG_ON(drm_buddy_block_size(mm, root) < chunk_size);
@@ -147,6 +149,7 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
i++;
} while (size);
+ list_del(&leaf);
return 0;
out_free_roots:
@@ -205,6 +208,9 @@ static int split_block(struct drm_buddy *mm,
mark_free(mm, block->left);
mark_free(mm, block->right);
+ list_add(&block->right->leaf_link, &block->leaf_link);
+ list_add(&block->left->leaf_link, &block->leaf_link);
+ list_del(&block->leaf_link);
mark_split(block);
return 0;
@@ -256,6 +262,9 @@ static void __drm_buddy_free(struct drm_buddy *mm,
break;
list_del(&buddy->link);
+ list_add(&parent->leaf_link, &block->leaf_link);
+ list_del(&buddy->leaf_link);
+ list_del(&block->leaf_link);
drm_block_free(mm, block);
drm_block_free(mm, buddy);
@@ -386,6 +395,78 @@ alloc_range_bias(struct drm_buddy *mm,
return ERR_PTR(err);
}
+static struct drm_buddy_block *
+find_continuous_blocks(struct drm_buddy *mm,
+ int order,
+ unsigned long flags,
+ struct drm_buddy_block **rblock)
+{
+ struct list_head *head = &mm->free_list[order];
+ struct drm_buddy_block *free_block, *max_block = NULL, *end, *begin;
+ u64 pages = BIT(order + 1);
+ u64 cur_pages;
+
+ list_for_each_entry(free_block, head, link) {
+ if (max_block) {
+ if (!(flags & DRM_BUDDY_TOPDOWN_ALLOCATION))
+ break;
+
+ if (drm_buddy_block_offset(free_block) <
+ drm_buddy_block_offset(max_block))
+ continue;
+ }
+
+ cur_pages = BIT(order);
+ begin = end = free_block;
+ while (true) {
+ struct drm_buddy_block *prev, *next;
+ int prev_order, next_order;
+
+ prev = list_prev_entry(begin, leaf_link);
+ if (!drm_buddy_block_is_free(prev) ||
+ drm_buddy_block_offset(prev) >
+ drm_buddy_block_offset(begin)) {
+ prev = NULL;
+ }
+ next = list_next_entry(end, leaf_link);
+ if (!drm_buddy_block_is_free(next) ||
+ drm_buddy_block_offset(next) <
+ drm_buddy_block_offset(end)) {
+ next = NULL;
+ }
+ if (!prev && !next)
+ break;
+
+ prev_order = prev ? drm_buddy_block_order(prev) : -1;
+ next_order = next ? drm_buddy_block_order(next) : -1;
+ if (next_order >= prev_order) {
+ BUG_ON(drm_buddy_block_offset(end) +
+ drm_buddy_block_size(mm, end) !=
+ drm_buddy_block_offset(next));
+ end = next;
+ cur_pages += BIT(drm_buddy_block_order(next));
+ }
+ if (prev_order >= next_order) {
+ BUG_ON(drm_buddy_block_offset(prev) +
+ drm_buddy_block_size(mm, prev) !=
+ drm_buddy_block_offset(begin));
+ begin = prev;
+ cur_pages += BIT(drm_buddy_block_order(prev));
+ }
+ if (pages == cur_pages)
+ break;
+ BUG_ON(pages < cur_pages);
+ }
+
+ if (pages > cur_pages)
+ continue;
+
+ *rblock = end;
+ max_block = begin;
+ }
+ return max_block;
+}
+
static struct drm_buddy_block *
get_maxblock(struct list_head *head)
{
@@ -637,7 +718,7 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
struct list_head *blocks,
unsigned long flags)
{
- struct drm_buddy_block *block = NULL;
+ struct drm_buddy_block *block = NULL, *rblock = NULL;
unsigned int min_order, order;
unsigned long pages;
LIST_HEAD(allocated);
@@ -689,17 +770,30 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
break;
if (order-- == min_order) {
+ if (!(flags & DRM_BUDDY_RANGE_ALLOCATION) &&
+ min_order != 0 && pages == BIT(order + 1)) {
+ block = find_continuous_blocks(mm,
+ order,
+ flags,
+ &rblock);
+ if (block)
+ break;
+ }
err = -ENOSPC;
goto err_free;
}
} while (1);
- mark_allocated(block);
- mm->avail -= drm_buddy_block_size(mm, block);
- kmemleak_update_trace(block);
- list_add_tail(&block->link, &allocated);
-
- pages -= BIT(order);
+ do {
+ mark_allocated(block);
+ mm->avail -= drm_buddy_block_size(mm, block);
+ kmemleak_update_trace(block);
+ list_add_tail(&block->link, &allocated);
+ pages -= BIT(drm_buddy_block_order(block));
+ if (block == rblock || !rblock)
+ break;
+ block = list_next_entry(block, leaf_link);
+ } while (true);
if (!pages)
break;
diff --git a/include/drm/drm_buddy.h b/include/drm/drm_buddy.h
index 572077ff8ae7..c5437bd4f4f3 100644
--- a/include/drm/drm_buddy.h
+++ b/include/drm/drm_buddy.h
@@ -50,6 +50,7 @@ struct drm_buddy_block {
*/
struct list_head link;
struct list_head tmp_link;
+ struct list_head leaf_link;
};
/* Order-zero must be at least PAGE_SIZE */