btrfs: turn fs_info member buffer_radix into XArray

… named 'extent_buffers'. Also adjust all usages of this object to use
the XArray API, which greatly simplifies the code as it takes care of
locking and is generally easier to use and understand, providing
notionally simpler array semantics.

Also perform some light refactoring.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Gabriel Niebler <gniebler@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 48 insertions, 74 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 07888cce3bce..66636e43e339 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2965,7 +2965,7 @@ static void begin_page_read(struct btrfs_fs_info *fs_info, struct page *page)
 }
 
 /*
- * Find extent buffer for a givne bytenr.
+ * Find extent buffer for a given bytenr.
  *
  * This is for end_bio_extent_readpage(), thus we can't do any unsafe locking
  * in endio context.
@@ -2984,11 +2984,9 @@ static struct extent_buffer *find_extent_buffer_readpage(
 		return (struct extent_buffer *)page->private;
 	}
 
-	/* For subpage case, we need to lookup buffer radix tree */
-	rcu_read_lock();
-	eb = radix_tree_lookup(&fs_info->buffer_radix,
-			       bytenr >> fs_info->sectorsize_bits);
-	rcu_read_unlock();
+	/* For subpage case, we need to lookup extent buffer xarray */
+	eb = xa_load(&fs_info->extent_buffers,
+		     bytenr >> fs_info->sectorsize_bits);
 	ASSERT(eb);
 	return eb;
 }
@@ -4447,8 +4445,8 @@ static struct extent_buffer *find_extent_buffer_nolock(
 	struct extent_buffer *eb;
 
 	rcu_read_lock();
-	eb = radix_tree_lookup(&fs_info->buffer_radix,
-			       start >> fs_info->sectorsize_bits);
+	eb = xa_load(&fs_info->extent_buffers,
+		     start >> fs_info->sectorsize_bits);
 	if (eb && atomic_inc_not_zero(&eb->refs)) {
 		rcu_read_unlock();
 		return eb;
@@ -6141,24 +6139,22 @@ struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
 	if (!eb)
 		return ERR_PTR(-ENOMEM);
 	eb->fs_info = fs_info;
-again:
-	ret = radix_tree_preload(GFP_NOFS);
-	if (ret) {
-		exists = ERR_PTR(ret);
-		goto free_eb;
-	}
-	spin_lock(&fs_info->buffer_lock);
-	ret = radix_tree_insert(&fs_info->buffer_radix,
-				start >> fs_info->sectorsize_bits, eb);
-	spin_unlock(&fs_info->buffer_lock);
-	radix_tree_preload_end();
-	if (ret == -EEXIST) {
-		exists = find_extent_buffer(fs_info, start);
-		if (exists)
+
+	do {
+		ret = xa_insert(&fs_info->extent_buffers,
+				start >> fs_info->sectorsize_bits,
+				eb, GFP_NOFS);
+		if (ret == -ENOMEM) {
+			exists = ERR_PTR(ret);
 			goto free_eb;
-		else
-			goto again;
-	}
+		}
+		if (ret == -EBUSY) {
+			exists = find_extent_buffer(fs_info, start);
+			if (exists)
+				goto free_eb;
+		}
+	} while (ret);
+
 	check_buffer_tree_ref(eb);
 	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
 
@@ -6333,25 +6329,22 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 	}
 	if (uptodate)
 		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
-again:
-	ret = radix_tree_preload(GFP_NOFS);
-	if (ret) {
-		exists = ERR_PTR(ret);
-		goto free_eb;
-	}
-
-	spin_lock(&fs_info->buffer_lock);
-	ret = radix_tree_insert(&fs_info->buffer_radix,
-				start >> fs_info->sectorsize_bits, eb);
-	spin_unlock(&fs_info->buffer_lock);
-	radix_tree_preload_end();
-	if (ret == -EEXIST) {
-		exists = find_extent_buffer(fs_info, start);
-		if (exists)
+
+	do {
+		ret = xa_insert(&fs_info->extent_buffers,
+				start >> fs_info->sectorsize_bits,
+				eb, GFP_NOFS);
+		if (ret == -ENOMEM) {
+			exists = ERR_PTR(ret);
 			goto free_eb;
-		else
-			goto again;
-	}
+		}
+		if (ret == -EBUSY) {
+			exists = find_extent_buffer(fs_info, start);
+			if (exists)
+				goto free_eb;
+		}
+	} while (ret);
+
 	/* add one reference for the tree */
 	check_buffer_tree_ref(eb);
 	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
@@ -6396,10 +6389,8 @@ static int release_extent_buffer(struct extent_buffer *eb)
 
 			spin_unlock(&eb->refs_lock);
 
-			spin_lock(&fs_info->buffer_lock);
-			radix_tree_delete(&fs_info->buffer_radix,
-					  eb->start >> fs_info->sectorsize_bits);
-			spin_unlock(&fs_info->buffer_lock);
+			xa_erase(&fs_info->extent_buffers,
+				 eb->start >> fs_info->sectorsize_bits);
 		} else {
 			spin_unlock(&eb->refs_lock);
 		}
@@ -7344,42 +7335,25 @@ void memmove_extent_buffer(const struct extent_buffer *dst,
 	}
 }
 
-#define GANG_LOOKUP_SIZE	16
 static struct extent_buffer *get_next_extent_buffer(
 		struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
 {
-	struct extent_buffer *gang[GANG_LOOKUP_SIZE];
-	struct extent_buffer *found = NULL;
+	struct extent_buffer *eb;
+	unsigned long index;
 	u64 page_start = page_offset(page);
-	u64 cur = page_start;
 
 	ASSERT(in_range(bytenr, page_start, PAGE_SIZE));
 	lockdep_assert_held(&fs_info->buffer_lock);
 
-	while (cur < page_start + PAGE_SIZE) {
-		int ret;
-		int i;
-
-		ret = radix_tree_gang_lookup(&fs_info->buffer_radix,
-				(void **)gang, cur >> fs_info->sectorsize_bits,
-				min_t(unsigned int, GANG_LOOKUP_SIZE,
-				      PAGE_SIZE / fs_info->nodesize));
-		if (ret == 0)
-			goto out;
-		for (i = 0; i < ret; i++) {
-			/* Already beyond page end */
-			if (gang[i]->start >= page_start + PAGE_SIZE)
-				goto out;
-			/* Found one */
-			if (gang[i]->start >= bytenr) {
-				found = gang[i];
-				goto out;
-			}
-		}
-		cur = gang[ret - 1]->start + gang[ret - 1]->len;
+	xa_for_each_start(&fs_info->extent_buffers, index, eb,
+			  page_start >> fs_info->sectorsize_bits) {
+		if (in_range(eb->start, page_start, PAGE_SIZE))
+			return eb;
+		else if (eb->start >= page_start + PAGE_SIZE)
+		        /* Already beyond page end */
+			return NULL;
 	}
-out:
-	return found;
+	return NULL;
 }
 
 static int try_release_subpage_extent_buffer(struct page *page)