The new function, write_one_subpage_eb(), as a subroutine for subpage
metadata write, will handle the extent buffer bio submission.
The major differences between the new write_one_subpage_eb() and
write_one_eb() is:
- No page locking
When entering write_one_subpage_eb() the page is no longer locked.
We only lock the page for its status update, and unlock immediately.
Now we completely rely on extent io tree locking.
- Extra bitmap update along with page status update
Now page dirty and writeback is controlled by
btrfs_subpage::dirty_bitmap and btrfs_subpage::writeback_bitmap.
They both follow the schema that any sector is dirty/writeback, then
the full page get dirty/writeback.
- When to update the nr_written number
Now we take a short cut, if we have cleared the last dirty bit of the
page, we update nr_written.
This is not completely perfect, but should emulate the old behavior
good enough.
Signed-off-by: Qu Wenruo <w...@suse.com>
---
fs/btrfs/extent_io.c | 55 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 21a14b1cb065..f32163a465ec 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4196,6 +4196,58 @@ static void end_bio_extent_buffer_writepage(struct bio
*bio)
bio_put(bio);
}
+/*
+ * Unlike the work in write_one_eb(), we rely completely on extent locking.
+ * Page locking is only utizlied at minimal to keep the VM code happy.
+ *
+ * Caller should still call write_one_eb() other than this function directly.
+ * As write_one_eb() has extra prepration before submitting the extent buffer.
+ */
+static int write_one_subpage_eb(struct extent_buffer *eb,
+ struct writeback_control *wbc,
+ struct extent_page_data *epd)
+{
+ struct btrfs_fs_info *fs_info = eb->fs_info;
+ struct page *page = eb->pages[0];
+ unsigned int write_flags = wbc_to_write_flags(wbc) | REQ_META;
+ bool no_dirty_ebs = false;
+ int ret;
+
+ /* clear_page_dirty_for_io() in subpage helper need page locked. */
+ lock_page(page);
+ btrfs_subpage_set_writeback(fs_info, page, eb->start, eb->len);
+
+ /* If we're the last dirty bit to update nr_written */
+ no_dirty_ebs = btrfs_subpage_clear_and_test_dirty(fs_info, page,
+ eb->start, eb->len);
+ if (no_dirty_ebs)
+ clear_page_dirty_for_io(page);
+
+ ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc, page,
+ eb->start, eb->len, eb->start - page_offset(page),
+ &epd->bio, end_bio_extent_buffer_writepage, 0, 0, 0,
+ false);
+ if (ret) {
+ btrfs_subpage_clear_writeback(fs_info, page, eb->start,
+ eb->len);
+ set_btree_ioerr(page, eb);
+ unlock_page(page);
+
+ if (atomic_dec_and_test(&eb->io_pages))
+ end_extent_buffer_writeback(eb);
+ return -EIO;
+ }
+ unlock_page(page);
+ /*
+ * Submission finishes without problem, if no range of the page is
+ * dirty anymore, we have submitted a page.
+ * Update the nr_written in wbc.
+ */
+ if (no_dirty_ebs)
+ update_nr_written(wbc, 1);
+ return ret;
+}
+
static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
struct writeback_control *wbc,
struct extent_page_data *epd)
@@ -4227,6 +4279,9 @@ static noinline_for_stack int write_one_eb(struct
extent_buffer *eb,
memzero_extent_buffer(eb, start, end - start);
}
+ if (eb->fs_info->sectorsize < PAGE_SIZE)
+ return write_one_subpage_eb(eb, wbc, epd);
+
