btrfs: discard one region at a time in async discard

The prior two patches added discarding via a background workqueue. This
just piggybacked off of the fstrim code to trim the whole block at once.
Well inevitably this is worse performance wise and will aggressively
overtrim. But it was nice to plumb the other infrastructure to keep the
patches easier to review.

This adds the real goal of this series which is discarding slowly (ie. a
slow long running fstrim). The discarding is split into two phases,
extents and then bitmaps. The reason for this is two fold. First, the
bitmap regions overlap the extent regions. Second, discarding the
extents first will let the newly trimmed bitmaps have the highest chance
of coalescing when being readded to the free space cache.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 102 insertions, 29 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 3c2796bb6498..2e8fbd67ec9b 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -3322,8 +3322,12 @@ static int do_trimming(struct btrfs_block_group *block_group,
 	return ret;
 }
 
+/*
+ * If @async is set, then we will trim 1 region and return.
+ */
 static int trim_no_bitmap(struct btrfs_block_group *block_group,
-			  u64 *total_trimmed, u64 start, u64 end, u64 minlen)
+			  u64 *total_trimmed, u64 start, u64 end, u64 minlen,
+			  bool async)
 {
 	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
 	struct btrfs_free_space *entry;
@@ -3340,36 +3344,25 @@ static int trim_no_bitmap(struct btrfs_block_group *block_group,
 		mutex_lock(&ctl->cache_writeout_mutex);
 		spin_lock(&ctl->tree_lock);
 
-		if (ctl->free_space < minlen) {
-			spin_unlock(&ctl->tree_lock);
-			mutex_unlock(&ctl->cache_writeout_mutex);
-			break;
-		}
+		if (ctl->free_space < minlen)
+			goto out_unlock;
 
 		entry = tree_search_offset(ctl, start, 0, 1);
-		if (!entry) {
-			spin_unlock(&ctl->tree_lock);
-			mutex_unlock(&ctl->cache_writeout_mutex);
-			break;
-		}
+		if (!entry)
+			goto out_unlock;
 
-		/* skip bitmaps */
-		while (entry->bitmap) {
+		/* Skip bitmaps and if async, already trimmed entries */
+		while (entry->bitmap ||
+		       (async && btrfs_free_space_trimmed(entry))) {
 			node = rb_next(&entry->offset_index);
-			if (!node) {
-				spin_unlock(&ctl->tree_lock);
-				mutex_unlock(&ctl->cache_writeout_mutex);
-				goto out;
-			}
+			if (!node)
+				goto out_unlock;
 			entry = rb_entry(node, struct btrfs_free_space,
 					 offset_index);
 		}
 
-		if (entry->offset >= end) {
-			spin_unlock(&ctl->tree_lock);
-			mutex_unlock(&ctl->cache_writeout_mutex);
-			break;
-		}
+		if (entry->offset >= end)
+			goto out_unlock;
 
 		extent_start = entry->offset;
 		extent_bytes = entry->bytes;
@@ -3394,10 +3387,15 @@ static int trim_no_bitmap(struct btrfs_block_group *block_group,
 		ret = do_trimming(block_group, total_trimmed, start, bytes,
 				  extent_start, extent_bytes, extent_trim_state,
 				  &trim_entry);
-		if (ret)
+		if (ret) {
+			block_group->discard_cursor = start + bytes;
 			break;
+		}
 next:
 		start += bytes;
+		block_group->discard_cursor = start;
+		if (async && *total_trimmed)
+			break;
 
 		if (fatal_signal_pending(current)) {
 			ret = -ERESTARTSYS;
@@ -3406,7 +3404,14 @@ next:
 
 		cond_resched();
 	}
-out:
+
+	return ret;
+
+out_unlock:
+	block_group->discard_cursor = btrfs_block_group_end(block_group);
+	spin_unlock(&ctl->tree_lock);
+	mutex_unlock(&ctl->cache_writeout_mutex);
+
 	return ret;
 }
 
@@ -3441,8 +3446,12 @@ static void end_trimming_bitmap(struct btrfs_free_space *entry)
 		entry->trim_state = BTRFS_TRIM_STATE_TRIMMED;
 }
 
+/*
+ * If @async is set, then we will trim 1 region and return.
+ */
 static int trim_bitmaps(struct btrfs_block_group *block_group,
-			u64 *total_trimmed, u64 start, u64 end, u64 minlen)
+			u64 *total_trimmed, u64 start, u64 end, u64 minlen,
+			bool async)
 {
 	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
 	struct btrfs_free_space *entry;
@@ -3459,13 +3468,16 @@ static int trim_bitmaps(struct btrfs_block_group *block_group,
 		spin_lock(&ctl->tree_lock);
 
 		if (ctl->free_space < minlen) {
+			block_group->discard_cursor =
+				btrfs_block_group_end(block_group);
 			spin_unlock(&ctl->tree_lock);
 			mutex_unlock(&ctl->cache_writeout_mutex);
 			break;
 		}
 
 		entry = tree_search_offset(ctl, offset, 1, 0);
-		if (!entry || btrfs_free_space_trimmed(entry)) {
+		if (!entry || (async && start == offset &&
+			       btrfs_free_space_trimmed(entry))) {
 			spin_unlock(&ctl->tree_lock);
 			mutex_unlock(&ctl->cache_writeout_mutex);
 			next_bitmap = true;
@@ -3498,6 +3510,16 @@ static int trim_bitmaps(struct btrfs_block_group *block_group,
 			goto next;
 		}
 
+		/*
+		 * We already trimmed a region, but are using the locking above
+		 * to reset the trim_state.
+		 */
+		if (async && *total_trimmed) {
+			spin_unlock(&ctl->tree_lock);
+			mutex_unlock(&ctl->cache_writeout_mutex);
+			goto out;
+		}
+
 		bytes = min(bytes, end - start);
 		if (bytes < minlen) {
 			entry->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
@@ -3520,6 +3542,8 @@ static int trim_bitmaps(struct btrfs_block_group *block_group,
 				  start, bytes, 0, &trim_entry);
 		if (ret) {
 			reset_trimming_bitmap(ctl, offset);
+			block_group->discard_cursor =
+				btrfs_block_group_end(block_group);
 			break;
 		}
 next:
@@ -3529,6 +3553,7 @@ next:
 		} else {
 			start += bytes;
 		}
+		block_group->discard_cursor = start;
 
 		if (fatal_signal_pending(current)) {
 			if (start != offset)
@@ -3540,6 +3565,10 @@ next:
 		cond_resched();
 	}
 
+	if (offset >= end)
+		block_group->discard_cursor = end;
+
+out:
 	return ret;
 }
 
@@ -3600,11 +3629,11 @@ int btrfs_trim_block_group(struct btrfs_block_group *block_group,
 	btrfs_get_block_group_trimming(block_group);
 	spin_unlock(&block_group->lock);
 
-	ret = trim_no_bitmap(block_group, trimmed, start, end, minlen);
+	ret = trim_no_bitmap(block_group, trimmed, start, end, minlen, false);
 	if (ret)
 		goto out;
 
-	ret = trim_bitmaps(block_group, trimmed, start, end, minlen);
+	ret = trim_bitmaps(block_group, trimmed, start, end, minlen, false);
 	div64_u64_rem(end, BITS_PER_BITMAP * ctl->unit, &rem);
 	/* If we ended in the middle of a bitmap, reset the trimming flag */
 	if (rem)
@@ -3614,6 +3643,50 @@ out:
 	return ret;
 }
 
+int btrfs_trim_block_group_extents(struct btrfs_block_group *block_group,
+				   u64 *trimmed, u64 start, u64 end, u64 minlen,
+				   bool async)
+{
+	int ret;
+
+	*trimmed = 0;
+
+	spin_lock(&block_group->lock);
+	if (block_group->removed) {
+		spin_unlock(&block_group->lock);
+		return 0;
+	}
+	btrfs_get_block_group_trimming(block_group);
+	spin_unlock(&block_group->lock);
+
+	ret = trim_no_bitmap(block_group, trimmed, start, end, minlen, async);
+	btrfs_put_block_group_trimming(block_group);
+
+	return ret;
+}
+
+int btrfs_trim_block_group_bitmaps(struct btrfs_block_group *block_group,
+				   u64 *trimmed, u64 start, u64 end, u64 minlen,
+				   bool async)
+{
+	int ret;
+
+	*trimmed = 0;
+
+	spin_lock(&block_group->lock);
+	if (block_group->removed) {
+		spin_unlock(&block_group->lock);
+		return 0;
+	}
+	btrfs_get_block_group_trimming(block_group);
+	spin_unlock(&block_group->lock);
+
+	ret = trim_bitmaps(block_group, trimmed, start, end, minlen, async);
+	btrfs_put_block_group_trimming(block_group);
+
+	return ret;
+}
+
 /*
  * Find the left-most item in the cache tree, and then return the
  * smallest inode number in the item.