btrfs: make attach_extent_buffer_page() handle subpage case

For subpage case, we need to allocate additional memory for each
metadata page.

So we need to:

- Allow attach_extent_buffer_page() to return int to indicate allocation
  failure

- Allow manually pre-allocate subpage memory for alloc_extent_buffer()
  As we don't want to use GFP_ATOMIC under spinlock, we introduce
  btrfs_alloc_subpage() and btrfs_free_subpage() functions for this
  purpose.
  (The simple wrap for btrfs_free_subpage() is for later convert to
   kmem_cache. Already internally tested without problem)

- Preallocate btrfs_subpage structure for alloc_extent_buffer()
  We don't want to call memory allocation with spinlock held, so
  do preallocation before we acquire mapping->private_lock.

- Handle subpage and regular case differently in
  attach_extent_buffer_page()
  For regular case, no change, just do the usual thing.
  For subpage case, allocate new memory or use the preallocated memory.

For future subpage metadata, we will make use of radix tree to grab
extent buffer.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 24 insertions, 6 deletions

diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index a3e5b6a13d54..61b28dfca20c 100644
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -7,7 +7,8 @@
 int btrfs_attach_subpage(const struct btrfs_fs_info *fs_info,
 			 struct page *page, enum btrfs_subpage_type type)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_subpage *subpage = NULL;
+	int ret;
 
 	/*
 	 * We have cases like a dummy extent buffer page, which is not mappped
@@ -19,11 +20,9 @@ int btrfs_attach_subpage(const struct btrfs_fs_info *fs_info,
 	if (fs_info->sectorsize == PAGE_SIZE || PagePrivate(page))
 		return 0;
 
-	subpage = kzalloc(sizeof(struct btrfs_subpage), GFP_NOFS);
-	if (!subpage)
-		return -ENOMEM;
-
-	spin_lock_init(&subpage->lock);
+	ret = btrfs_alloc_subpage(fs_info, &subpage, type);
+	if (ret < 0)
+		return ret;
 	attach_page_private(page, subpage);
 	return 0;
 }
@@ -39,5 +38,24 @@ void btrfs_detach_subpage(const struct btrfs_fs_info *fs_info,
 
 	subpage = (struct btrfs_subpage *)detach_page_private(page);
 	ASSERT(subpage);
+	btrfs_free_subpage(subpage);
+}
+
+int btrfs_alloc_subpage(const struct btrfs_fs_info *fs_info,
+			struct btrfs_subpage **ret,
+			enum btrfs_subpage_type type)
+{
+	if (fs_info->sectorsize == PAGE_SIZE)
+		return 0;
+
+	*ret = kzalloc(sizeof(struct btrfs_subpage), GFP_NOFS);
+	if (!*ret)
+		return -ENOMEM;
+	spin_lock_init(&(*ret)->lock);
+	return 0;
+}
+
+void btrfs_free_subpage(struct btrfs_subpage *subpage)
+{
 	kfree(subpage);
 }