btrfs: introduce struct to consolidate extent buffer write context

Introduce btrfs_eb_write_context to consolidate writeback_control and the
exntent buffer context.  This will help adding a block group context as
well.

While at it, move the eb context setting before
btrfs_check_meta_write_pointer(). We can set it here because we anyway need
to skip pages in the same eb if that eb is rejected by
btrfs_check_meta_write_pointer().
Suggested-by: Christoph Hellwig <hch@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -1805,9 +1805,9 @@ static int submit_eb_subpage(struct page *page, struct writeback_control *wbc)
  * previous call.
  * Return <0 for fatal error.
  */
-static int submit_eb_page(struct page *page, struct writeback_control *wbc,
-			  struct extent_buffer **eb_context)
+static int submit_eb_page(struct page *page, struct btrfs_eb_write_context *ctx)
 {
+	struct writeback_control *wbc = ctx->wbc;
 	struct address_space *mapping = page->mapping;
 	struct btrfs_block_group *cache = NULL;
 	struct extent_buffer *eb;
@@ -1836,7 +1836,7 @@ static int submit_eb_page(struct page *page, struct writeback_control *wbc,
 		return 0;
 	}
 
-	if (eb == *eb_context) {
+	if (eb == ctx->eb) {
 		spin_unlock(&mapping->private_lock);
 		return 0;
 	}
@@ -1845,6 +1845,8 @@ static int submit_eb_page(struct page *page, struct writeback_control *wbc,
 	if (!ret)
 		return 0;
 
+	ctx->eb = eb;
+
 	if (!btrfs_check_meta_write_pointer(eb->fs_info, eb, &cache)) {
 		/*
 		 * If for_sync, this hole will be filled with
@@ -1858,8 +1860,6 @@ static int submit_eb_page(struct page *page, struct writeback_control *wbc,
 		return ret;
 	}
 
-	*eb_context = eb;
-
 	if (!lock_extent_buffer_for_io(eb, wbc)) {
 		btrfs_revert_meta_write_pointer(cache, eb);
 		if (cache)
@@ -1882,7 +1882,7 @@ static int submit_eb_page(struct page *page, struct writeback_control *wbc,
 int btree_write_cache_pages(struct address_space *mapping,
 				   struct writeback_control *wbc)
 {
-	struct extent_buffer *eb_context = NULL;
+	struct btrfs_eb_write_context ctx = { .wbc = wbc };
 	struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
 	int ret = 0;
 	int done = 0;
@@ -1924,7 +1924,7 @@ int btree_write_cache_pages(struct address_space *mapping,
 		for (i = 0; i < nr_folios; i++) {
 			struct folio *folio = fbatch.folios[i];
 
-			ret = submit_eb_page(&folio->page, wbc, &eb_context);
+			ret = submit_eb_page(&folio->page, &ctx);
 			if (ret == 0)
 				continue;
 			if (ret < 0) {

fs/btrfs/extent_io.h

@@ -93,6 +93,11 @@ struct extent_buffer {
 #endif
 };
 
+struct btrfs_eb_write_context {
+	struct writeback_control *wbc;
+	struct extent_buffer *eb;
+};
+
 /*
  * Get the correct offset inside the page of extent buffer.
  *