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

Ritesh Harjani (IBM)
2023-06-05T10:56:05Z

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@in.ibm.com>
Reported-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
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