btrfs: simplify subpage handling of write_one_eb()

Currently inside write_one_eb() we have two different ways of handling
subpage and regular metadata.

The differences are:

- Extra offset/length calculation when adding the folio range to bio for
  subpage cases
- Only decrease wbc->nr_to_write if the whole page is no longer dirty
  for subpage cases
- Use subpage helper for subpage cases

Merge the tow ways into a shared one:

- Always calculate the to-be-queued range
  So that bio_add_folio() can use the same calculated resulted length
  and offset for both cases.

- Use btrfs_meta_folio_clear_dirty() and
  btrfs_meta_folio_set_writeback() helpers
  This will cover both cases.

- Only decrease wbc->nr_to_write if the folio is no longer dirty
  Since we have the folio locked, no one else can modify the folio dirty
  flags (set_extent_buffer_dirty() will also lock the folio for subpage
  cases).

  Thus after our btrfs_meta_folio_clear_dirty() call, if the whole folio
  is no longer dirty, we're submitting the last dirty eb of the folio,
  and can decrease wbc->nr_to_write properly.

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

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 354dd25225311d7f34270ef7fc1c9ea4783f2e36..b23d27cfdf14604a768a78a247c5a26122819961 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1786,6 +1786,7 @@ static noinline_for_stack void write_one_eb(struct extent_buffer *eb,
 {
        struct btrfs_fs_info *fs_info = eb->fs_info;
        struct btrfs_bio *bbio;
+       const int num_folios = num_extent_folios(eb);
 
        prepare_eb_write(eb);
 
@@ -1797,38 +1798,21 @@ static noinline_for_stack void write_one_eb(struct extent_buffer *eb,
        wbc_init_bio(wbc, &bbio->bio);
        bbio->inode = BTRFS_I(eb->fs_info->btree_inode);
        bbio->file_offset = eb->start;
-       if (btrfs_meta_is_subpage(fs_info)) {
-               struct folio *folio = eb->folios[0];
-               bool ret;
+       for (int i = 0; i < num_folios; i++) {
+               struct folio *folio = eb->folios[i];
+               u64 range_start = max_t(u64, eb->start, folio_pos(folio));
+               u32 range_len = min_t(u64, folio_pos(folio) + folio_size(folio),
+                                     eb->start + eb->len) - range_start;
 
                folio_lock(folio);
-               btrfs_subpage_set_writeback(fs_info, folio, eb->start, eb->len);
-               if (btrfs_subpage_clear_and_test_dirty(fs_info, folio, eb->start,
-                                                      eb->len)) {
-                       folio_clear_dirty_for_io(folio);
-                       wbc->nr_to_write--;
-               }
-               ret = bio_add_folio(&bbio->bio, folio, eb->len,
-                                   eb->start - folio_pos(folio));
-               ASSERT(ret);
-               wbc_account_cgroup_owner(wbc, folio, eb->len);
-               folio_unlock(folio);
-       } else {
-               int num_folios = num_extent_folios(eb);
-
-               for (int i = 0; i < num_folios; i++) {
-                       struct folio *folio = eb->folios[i];
-                       bool ret;
-
-                       folio_lock(folio);
-                       folio_clear_dirty_for_io(folio);
-                       folio_start_writeback(folio);
-                       ret = bio_add_folio(&bbio->bio, folio, eb->folio_size, 0);
-                       ASSERT(ret);
-                       wbc_account_cgroup_owner(wbc, folio, eb->folio_size);
+               btrfs_meta_folio_clear_dirty(fs_info, folio, eb->start, eb->len);
+               btrfs_meta_folio_set_writeback(fs_info, folio, eb->start, eb->len);
+               if (!folio_test_dirty(folio))
                        wbc->nr_to_write -= folio_nr_pages(folio);
-                       folio_unlock(folio);
-               }
+               bio_add_folio_nofail(&bbio->bio, folio, range_len,
+                                    offset_in_folio(folio, range_start));
+               wbc_account_cgroup_owner(wbc, folio, range_len);
+               folio_unlock(folio);
        }
        btrfs_submit_bbio(bbio, 0);
 }