Commit 2c73162d authored by Christoph Hellwig's avatar Christoph Hellwig Committed by David Sterba
Browse files

btrfs: improve the delalloc_to_write calculation in writepage_delalloc 



Currently writepage_delalloc adds to delalloc_to_write in every loop
operation.  That is not only more work than doing it once after the
loop, but can also over-increment the counter due to rounding errors
when a new loop iteration starts with an offset into a page.

Add a new page_start variable instead of recaculation that value over
and over, move the delalloc_to_write calculation out of the loop, use
the DIV_ROUND_UP helper instead of open coding it and remove the pointless
found local variable.

Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 0835d1e6

fs/btrfs/extent_io.c

+14 −15
Original line number Diff line number Diff line
@@ -1185,8 +1185,10 @@ static inline void contiguous_readpages(struct page *pages[], int nr_pages, 
static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,

		struct page *page, struct writeback_control *wbc)

{

	const u64 page_end = page_offset(page) + PAGE_SIZE - 1;

	u64 delalloc_start = page_offset(page);

	const u64 page_start = page_offset(page);

	const u64 page_end = page_start + PAGE_SIZE - 1;

	u64 delalloc_start = page_start;

	u64 delalloc_end = page_end;

	u64 delalloc_to_write = 0;

	/* How many pages are started by btrfs_run_delalloc_range() */

	unsigned long nr_written = 0;
@@ -1194,13 +1196,9 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode, 
	int page_started = 0;



	while (delalloc_start < page_end) {

		u64 delalloc_end = page_end;

		bool found;



		found = find_lock_delalloc_range(&inode->vfs_inode, page,

					       &delalloc_start,

					       &delalloc_end);

		if (!found) {

		delalloc_end = page_end;

		if (!find_lock_delalloc_range(&inode->vfs_inode, page,

					      &delalloc_start, &delalloc_end)) {

			delalloc_start = delalloc_end + 1;

			continue;

		}
@@ -1209,14 +1207,15 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode, 
		if (ret)

			return ret;



		delalloc_start = delalloc_end + 1;

	}



	/*

	 * delalloc_end is already one less than the total length, so

	 * we don't subtract one from PAGE_SIZE

	 */

		delalloc_to_write += (delalloc_end - delalloc_start +

				      PAGE_SIZE) >> PAGE_SHIFT;

		delalloc_start = delalloc_end + 1;

	}

	delalloc_to_write +=

		DIV_ROUND_UP(delalloc_end + 1 - page_start, PAGE_SIZE);

	if (wbc->nr_to_write < delalloc_to_write) {

		int thresh = 8192;