Commit e55a0de1 authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
Browse files

btrfs: rework page locking in __extent_writepage() 



Pages passed to __extent_writepage() are always locked, but they may be
locked by different functions.

There are two types of locked page for __extent_writepage():

- Page locked by plain lock_page()
  It should not have any subpage::writers count.
  Can be unlocked by unlock_page().
  This is the most common locked page for __extent_writepage() called
  inside extent_write_cache_pages() or extent_write_full_page().
  Rarer cases include the @locked_page from extent_write_locked_range().

- Page locked by lock_delalloc_pages()
  There is only one caller, all pages except @locked_page for
  extent_write_locked_range().
  In this case, we have to call subpage helper to handle the case.

So here we introduce a helper, btrfs_page_unlock_writer(), to allow
__extent_writepage() to unlock different locked pages.

And since for all other callers of __extent_writepage() their pages are
ensured to be locked by lock_page(), also add an extra check for
epd::extent_locked to unlock such pages directly.

Signed-off-by: default avatarQu Wenruo <wqu@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent d4088803

fs/btrfs/extent_io.c

+14 −1
Original line number Diff line number Diff line
@@ -4051,6 +4051,7 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc, 
			      struct extent_page_data *epd)

{

	struct inode *inode = page->mapping->host;

	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);

	const u64 page_start = page_offset(page);

	const u64 page_end = page_start + PAGE_SIZE - 1;

	int ret;
@@ -4138,7 +4139,19 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc, 
	 */

	if (PageError(page))

		end_extent_writepage(page, ret, page_start, page_end);

	if (epd->extent_locked) {

		/*

		 * If epd->extent_locked, it's from extent_write_locked_range(),

		 * the page can either be locked by lock_page() or

		 * process_one_page().

		 * Let btrfs_page_unlock_writer() handle both cases.

		 */

		ASSERT(wbc);

		btrfs_page_unlock_writer(fs_info, page, wbc->range_start,

					 wbc->range_end + 1 - wbc->range_start);

	} else {

		unlock_page(page);

	}

	ASSERT(ret <= 0);

	return ret;

}

fs/btrfs/subpage.c

+43 −0
Original line number Diff line number Diff line
@@ -690,3 +690,46 @@ void btrfs_page_assert_not_dirty(const struct btrfs_fs_info *fs_info, 
	ASSERT(PagePrivate(page) && page->private);

	ASSERT(subpage_test_bitmap_all_zero(fs_info, subpage, dirty));

}



/*

 * Handle different locked pages with different page sizes:

 *

 * - Page locked by plain lock_page()

 *   It should not have any subpage::writers count.

 *   Can be unlocked by unlock_page().

 *   This is the most common locked page for __extent_writepage() called

 *   inside extent_write_cache_pages() or extent_write_full_page().

 *   Rarer cases include the @locked_page from extent_write_locked_range().

 *

 * - Page locked by lock_delalloc_pages()

 *   There is only one caller, all pages except @locked_page for

 *   extent_write_locked_range().

 *   In this case, we have to call subpage helper to handle the case.

 */

void btrfs_page_unlock_writer(struct btrfs_fs_info *fs_info, struct page *page,

			      u64 start, u32 len)

{

	struct btrfs_subpage *subpage;



	ASSERT(PageLocked(page));

	/* For regular page size case, we just unlock the page */

	if (fs_info->sectorsize == PAGE_SIZE)

		return unlock_page(page);



	ASSERT(PagePrivate(page) && page->private);

	subpage = (struct btrfs_subpage *)page->private;



	/*

	 * For subpage case, there are two types of locked page.  With or

	 * without writers number.

	 *

	 * Since we own the page lock, no one else could touch subpage::writers

	 * and we are safe to do several atomic operations without spinlock.

	 */

	if (atomic_read(&subpage->writers))

		/* No writers, locked by plain lock_page() */

		return unlock_page(page);



	/* Have writers, use proper subpage helper to end it */

	btrfs_page_end_writer_lock(fs_info, page, start, len);

}

fs/btrfs/subpage.h

+2 −0
Original line number Diff line number Diff line
@@ -150,5 +150,7 @@ bool btrfs_subpage_clear_and_test_dirty(const struct btrfs_fs_info *fs_info, 


void btrfs_page_assert_not_dirty(const struct btrfs_fs_info *fs_info,

				 struct page *page);

void btrfs_page_unlock_writer(struct btrfs_fs_info *fs_info, struct page *page,

			      u64 start, u32 len);



#endif