From 35b6ddfa9626d1461d54eb203e9b6021d97dd13c Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Tue, 6 Apr 2021 08:36:01 +0800 Subject: [PATCH] btrfs: introduce write_one_subpage_eb() function 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 gets dirty/writeback. - When to update the nr_written number Now we take a shortcut, 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 well enough. Signed-off-by: Qu Wenruo Signed-off-by: David Sterba --- fs/btrfs/extent_io.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 8c006a182d6b..e0713b0753b7 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4197,6 +4197,56 @@ 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 utilized at minimum to keep the VMM code happy. + * + * Caller should still call write_one_eb() other than this function directly. + * As write_one_eb() has extra preparation 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 needs page locked */ + lock_page(page); + btrfs_subpage_set_writeback(fs_info, page, eb->start, eb->len); + + /* Check if this is 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 finished without problem, if no range of the page is + * dirty anymore, we have submitted a page. Update 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) @@ -4228,6 +4278,9 @@ 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); + for (i = 0; i < num_pages; i++) { struct page *p = eb->pages[i]; -- 2.11.0