[PATCHv7 6/6] iomap: Add per-block dirty state tracking to improve performance

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When filesystem blocksize is less than folio size (either with
mapping_large_folio_support() or with blocksize < pagesize) and when the
folio is uptodate in pagecache, then even a byte write can cause
an entire folio to be written to disk during writeback. This happens
because we currently don't have a mechanism to track per-block dirty
state within struct iomap_page. We currently only track uptodate state.

This patch implements support for tracking per-block dirty state in
iomap_page->state bitmap. This should help improve the filesystem write
performance and help reduce write amplification.

Performance testing of below fio workload reveals ~16x performance
improvement using nvme with XFS (4k blocksize) on Power (64K pagesize)
FIO reported write bw scores improved from around ~28 MBps to ~452 MBps.

1. <test_randwrite.fio>
[global]
	ioengine=psync
	rw=randwrite
	overwrite=1
	pre_read=1
	direct=0
	bs=4k
	size=1G
	dir=./
	numjobs=8
	fdatasync=1
	runtime=60
	iodepth=64
	group_reporting=1

[fio-run]

2. Also our internal performance team reported that this patch improves
   their database workload performance by around ~83% (with XFS on Power)

Reported-by: Aravinda Herle <araherle@xxxxxxxxxx>
Reported-by: Brian Foster <bfoster@xxxxxxxxxx>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
---
 fs/gfs2/aops.c         |   2 +-
 fs/iomap/buffered-io.c | 120 +++++++++++++++++++++++++++++++++++++++--
 fs/xfs/xfs_aops.c      |   2 +-
 fs/zonefs/file.c       |   2 +-
 include/linux/iomap.h  |   1 +
 5 files changed, 120 insertions(+), 7 deletions(-)

diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index a5f4be6b9213..75efec3c3b71 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -746,7 +746,7 @@ static const struct address_space_operations gfs2_aops = {
 	.writepages = gfs2_writepages,
 	.read_folio = gfs2_read_folio,
 	.readahead = gfs2_readahead,
-	.dirty_folio = filemap_dirty_folio,
+	.dirty_folio = iomap_dirty_folio,
 	.release_folio = iomap_release_folio,
 	.invalidate_folio = iomap_invalidate_folio,
 	.bmap = gfs2_bmap,
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 2a97d73edb96..e7d114b5b918 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -85,6 +85,63 @@ static void iomap_iop_set_range_uptodate(struct inode *inode,
 		folio_mark_uptodate(folio);
 }

+static bool iop_test_block_dirty(struct folio *folio, int block)
+{
+	struct iomap_page *iop = to_iomap_page(folio);
+	struct inode *inode = folio->mapping->host;
+	unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
+
+	return test_bit(block + blks_per_folio, iop->state);
+}
+
+static void iop_set_range_dirty(struct inode *inode, struct folio *folio,
+				size_t off, size_t len)
+{
+	struct iomap_page *iop = to_iomap_page(folio);
+	unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
+	unsigned int first_blk = off >> inode->i_blkbits;
+	unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
+	unsigned int nr_blks = last_blk - first_blk + 1;
+	unsigned long flags;
+
+	spin_lock_irqsave(&iop->state_lock, flags);
+	bitmap_set(iop->state, first_blk + blks_per_folio, nr_blks);
+	spin_unlock_irqrestore(&iop->state_lock, flags);
+}
+
+static void iomap_iop_set_range_dirty(struct inode *inode, struct folio *folio,
+				size_t off, size_t len)
+{
+	struct iomap_page *iop = to_iomap_page(folio);
+
+	if (iop)
+		iop_set_range_dirty(inode, folio, off, len);
+}
+
+static void iop_clear_range_dirty(struct inode *inode, struct folio *folio,
+				  size_t off, size_t len)
+{
+	struct iomap_page *iop = to_iomap_page(folio);
+	unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
+	unsigned int first_blk = off >> inode->i_blkbits;
+	unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
+	unsigned int nr_blks = last_blk - first_blk + 1;
+	unsigned long flags;
+
+	spin_lock_irqsave(&iop->state_lock, flags);
+	bitmap_clear(iop->state, first_blk + blks_per_folio, nr_blks);
+	spin_unlock_irqrestore(&iop->state_lock, flags);
+}
+
+static void iomap_iop_clear_range_dirty(struct inode *inode,
+				struct folio *folio, size_t off, size_t len)
+{
+	struct iomap_page *iop = to_iomap_page(folio);
+
+	if (iop)
+		iop_clear_range_dirty(inode, folio, off, len);
+}
+
 static struct iomap_page *iomap_iop_alloc(struct inode *inode,
 				struct folio *folio, unsigned int flags)
 {
@@ -100,12 +157,20 @@ static struct iomap_page *iomap_iop_alloc(struct inode *inode,
 	else
 		gfp = GFP_NOFS | __GFP_NOFAIL;

-	iop = kzalloc(struct_size(iop, state, BITS_TO_LONGS(nr_blocks)),
+	/*
+	 * iop->state tracks two sets of state flags when the
+	 * filesystem block size is smaller than the folio size.
+	 * The first state tracks per-block uptodate and the
+	 * second tracks per-block dirty state.
+	 */
+	iop = kzalloc(struct_size(iop, state, BITS_TO_LONGS(2 * nr_blocks)),
 		      gfp);
 	if (iop) {
 		spin_lock_init(&iop->state_lock);
 		if (folio_test_uptodate(folio))
-			bitmap_fill(iop->state, nr_blocks);
+			bitmap_set(iop->state, 0, nr_blocks);
+		if (folio_test_dirty(folio))
+			bitmap_set(iop->state, nr_blocks, nr_blocks);
 		folio_attach_private(folio, iop);
 	}
 	return iop;
@@ -533,6 +598,17 @@ void iomap_invalidate_folio(struct folio *folio, size_t offset, size_t len)
 }
 EXPORT_SYMBOL_GPL(iomap_invalidate_folio);

+bool iomap_dirty_folio(struct address_space *mapping, struct folio *folio)
+{
+	struct inode *inode = mapping->host;
+	size_t len = folio_size(folio);
+
+	iomap_iop_alloc(inode, folio, 0);
+	iomap_iop_set_range_dirty(inode, folio, 0, len);
+	return filemap_dirty_folio(mapping, folio);
+}
+EXPORT_SYMBOL_GPL(iomap_dirty_folio);
+
 static void
 iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
 {
@@ -739,6 +815,8 @@ static size_t __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
 		return 0;
 	iomap_iop_set_range_uptodate(inode, folio, offset_in_folio(folio, pos),
 				     len);
+	iomap_iop_set_range_dirty(inode, folio, offset_in_folio(folio, pos),
+				  copied);
 	filemap_dirty_folio(inode->i_mapping, folio);
 	return copied;
 }
@@ -908,6 +986,10 @@ static int iomap_write_delalloc_punch(struct inode *inode, struct folio *folio,
 		int (*punch)(struct inode *inode, loff_t offset, loff_t length))
 {
 	int ret = 0;
+	struct iomap_page *iop;
+	unsigned int first_blk, last_blk, i;
+	loff_t last_byte;
+	u8 blkbits = inode->i_blkbits;

 	if (!folio_test_dirty(folio))
 		return ret;
@@ -919,6 +1001,29 @@ static int iomap_write_delalloc_punch(struct inode *inode, struct folio *folio,
 		if (ret)
 			goto out;
 	}
+	/*
+	 * When we have per-block dirty tracking, there can be
+	 * blocks within a folio which are marked uptodate
+	 * but not dirty. In that case it is necessary to punch
+	 * out such blocks to avoid leaking any delalloc blocks.
+	 */
+	iop = to_iomap_page(folio);
+	if (!iop)
+		goto skip_iop_punch;
+
+	last_byte = min_t(loff_t, end_byte - 1,
+		(folio_next_index(folio) << PAGE_SHIFT) - 1);
+	first_blk = offset_in_folio(folio, start_byte) >> blkbits;
+	last_blk = offset_in_folio(folio, last_byte) >> blkbits;
+	for (i = first_blk; i <= last_blk; i++) {
+		if (!iop_test_block_dirty(folio, i)) {
+			ret = punch(inode, i << blkbits, 1 << blkbits);
+			if (ret)
+				goto out;
+		}
+	}
+
+skip_iop_punch:
 	/*
 	 * Make sure the next punch start is correctly bound to
 	 * the end of this data range, not the end of the folio.
@@ -1652,7 +1757,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 		struct writeback_control *wbc, struct inode *inode,
 		struct folio *folio, u64 end_pos)
 {
-	struct iomap_page *iop = iomap_iop_alloc(inode, folio, 0);
+	struct iomap_page *iop = to_iomap_page(folio);
 	struct iomap_ioend *ioend, *next;
 	unsigned len = i_blocksize(inode);
 	unsigned nblocks = i_blocks_per_folio(inode, folio);
@@ -1660,6 +1765,11 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 	int error = 0, count = 0, i;
 	LIST_HEAD(submit_list);

+	if (!iop && nblocks > 1) {
+		iop = iomap_iop_alloc(inode, folio, 0);
+		iomap_iop_set_range_dirty(inode, folio, 0, folio_size(folio));
+	}
+
 	WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) != 0);

 	/*
@@ -1668,7 +1778,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 	 * invalid, grab a new one.
 	 */
 	for (i = 0; i < nblocks && pos < end_pos; i++, pos += len) {
-		if (iop && !iop_test_block_uptodate(folio, i))
+		if (iop && !iop_test_block_dirty(folio, i))
 			continue;

 		error = wpc->ops->map_blocks(wpc, inode, pos);
@@ -1712,6 +1822,8 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 		}
 	}

+	iomap_iop_clear_range_dirty(inode, folio, 0,
+				    end_pos - folio_pos(folio));
 	folio_start_writeback(folio);
 	folio_unlock(folio);

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 2ef78aa1d3f6..77c7332ae197 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -578,7 +578,7 @@ const struct address_space_operations xfs_address_space_operations = {
 	.read_folio		= xfs_vm_read_folio,
 	.readahead		= xfs_vm_readahead,
 	.writepages		= xfs_vm_writepages,
-	.dirty_folio		= filemap_dirty_folio,
+	.dirty_folio		= iomap_dirty_folio,
 	.release_folio		= iomap_release_folio,
 	.invalidate_folio	= iomap_invalidate_folio,
 	.bmap			= xfs_vm_bmap,
diff --git a/fs/zonefs/file.c b/fs/zonefs/file.c
index 132f01d3461f..e508c8e97372 100644
--- a/fs/zonefs/file.c
+++ b/fs/zonefs/file.c
@@ -175,7 +175,7 @@ const struct address_space_operations zonefs_file_aops = {
 	.read_folio		= zonefs_read_folio,
 	.readahead		= zonefs_readahead,
 	.writepages		= zonefs_writepages,
-	.dirty_folio		= filemap_dirty_folio,
+	.dirty_folio		= iomap_dirty_folio,
 	.release_folio		= iomap_release_folio,
 	.invalidate_folio	= iomap_invalidate_folio,
 	.migrate_folio		= filemap_migrate_folio,
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index e2b836c2e119..eb9335c46bf3 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -264,6 +264,7 @@ bool iomap_is_partially_uptodate(struct folio *, size_t from, size_t count);
 struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos);
 bool iomap_release_folio(struct folio *folio, gfp_t gfp_flags);
 void iomap_invalidate_folio(struct folio *folio, size_t offset, size_t len);
+bool iomap_dirty_folio(struct address_space *mapping, struct folio *folio);
 int iomap_file_unshare(struct inode *inode, loff_t pos, loff_t len,
 		const struct iomap_ops *ops);
 int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,
--
2.40.1




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