On Tue, Jun 06, 2023 at 05:13:52PM +0530, Ritesh Harjani (IBM) wrote:
> 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_folio. We currently only track uptodate state.
>
> This patch implements support for tracking per-block dirty state in
> iomap_folio->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 | 126 +++++++++++++++++++++++++++++++++++++++--
> fs/xfs/xfs_aops.c | 2 +-
> fs/zonefs/file.c | 2 +-
> include/linux/iomap.h | 1 +
> 5 files changed, 126 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 2b72ca3ba37a..b99d611f1cd5 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -84,6 +84,70 @@ static void iomap_set_range_uptodate(struct folio *folio, size_t off,
> folio_mark_uptodate(folio);
> }
>
> +static inline bool iomap_iof_is_block_dirty(struct folio *folio,
> + struct iomap_folio *iof, int block)
> +{
> + struct inode *inode = folio->mapping->host;
> + unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
> +
> + return test_bit(block + blks_per_folio, iof->state);
> +}
> +
> +static void iomap_iof_clear_range_dirty(struct folio *folio,
> + struct iomap_folio *iof, size_t off, size_t len)
> +{
> + struct inode *inode = folio->mapping->host;
> + 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(&iof->state_lock, flags);
> + bitmap_clear(iof->state, first_blk + blks_per_folio, nr_blks);
> + spin_unlock_irqrestore(&iof->state_lock, flags);
> +}
> +
> +static void iomap_clear_range_dirty(struct folio *folio, size_t off, size_t len)
> +{
> + struct iomap_folio *iof = iomap_get_iof(folio);
> +
> + if (!iof)
> + return;
> + iomap_iof_clear_range_dirty(folio, iof, off, len);
> +}
> +
> +static void iomap_iof_set_range_dirty(struct inode *inode, struct folio *folio,
> + struct iomap_folio *iof, size_t off, size_t len)
> +{
> + 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(&iof->state_lock, flags);
> + bitmap_set(iof->state, first_blk + blks_per_folio, nr_blks);
> + spin_unlock_irqrestore(&iof->state_lock, flags);
> +}
> +
> +/*
> + * The reason we pass inode explicitly here is to avoid any race with truncate
> + * when iomap_set_range_dirty() gets called from iomap_dirty_folio().
> + * Check filemap_dirty_folio() & __folio_mark_dirty() for more details.
> + * Hence we explicitly pass mapping->host to iomap_set_range_dirty() from
> + * iomap_dirty_folio().
> + */
> +static void iomap_set_range_dirty(struct inode *inode, struct folio *folio,
> + size_t off, size_t len)
> +{
> + struct iomap_folio *iof = iomap_get_iof(folio);
> +
> + if (!iof)
> + return;
> + iomap_iof_set_range_dirty(inode, folio, iof, off, len);
> +}
> +
> static struct iomap_folio *iomap_iof_alloc(struct inode *inode,
> struct folio *folio, unsigned int flags)
> {
> @@ -99,12 +163,20 @@ static struct iomap_folio *iomap_iof_alloc(struct inode *inode,
> else
> gfp = GFP_NOFS | __GFP_NOFAIL;
>
> - iof = kzalloc(struct_size(iof, state, BITS_TO_LONGS(nr_blocks)),
> + /*
> + * iof->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.
> + */
> + iof = kzalloc(struct_size(iof, state, BITS_TO_LONGS(2 * nr_blocks)),
> gfp);
> if (iof) {
> spin_lock_init(&iof->state_lock);
> if (folio_test_uptodate(folio))
> - bitmap_fill(iof->state, nr_blocks);
> + bitmap_set(iof->state, 0, nr_blocks);
> + if (folio_test_dirty(folio))
> + bitmap_set(iof->state, nr_blocks, nr_blocks);
> folio_attach_private(folio, iof);
> }
> return iof;
> @@ -529,6 +601,17 @@ 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_iof_alloc(inode, folio, 0);
> + iomap_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)
> {
> @@ -733,6 +816,8 @@ static size_t __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
> if (unlikely(copied < len && !folio_test_uptodate(folio)))
> return 0;
> iomap_set_range_uptodate(folio, offset_in_folio(folio, pos), len);
> + iomap_set_range_dirty(inode, folio, offset_in_folio(folio, pos),
> + copied);
> filemap_dirty_folio(inode->i_mapping, folio);
> return copied;
> }
> @@ -902,6 +987,10 @@ 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_folio *iof;
> + unsigned int first_blk, last_blk, i;
> + loff_t last_byte;
> + u8 blkbits = inode->i_blkbits;
>
> if (!folio_test_dirty(folio))
> return ret;
> @@ -913,6 +1002,29 @@ 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.
> + */
> + iof = iomap_get_iof(folio);
> + if (!iof)
> + goto skip_iof_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 (!iomap_iof_is_block_dirty(folio, iof, i)) {
> + ret = punch(inode, i << blkbits, 1 << blkbits);
Isn't the second argument to punch() supposed to be the offset within
the file, not the offset within the folio?
I /almost/ wonder if this chunk should be its own static inline
iomap_iof_delalloc_punch function, but ... eh. My enthusiasm for
slicing and dicing is weak today.
--D
> + if (ret)
> + goto out;
> + }
> + }
> +
> +skip_iof_punch:
> /*
> * Make sure the next punch start is correctly bound to
> * the end of this data range, not the end of the folio.
> @@ -1646,7 +1758,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> struct writeback_control *wbc, struct inode *inode,
> struct folio *folio, u64 end_pos)
> {
> - struct iomap_folio *iof = iomap_iof_alloc(inode, folio, 0);
> + struct iomap_folio *iof = iomap_get_iof(folio);
> struct iomap_ioend *ioend, *next;
> unsigned len = i_blocksize(inode);
> unsigned nblocks = i_blocks_per_folio(inode, folio);
> @@ -1654,6 +1766,11 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> int error = 0, count = 0, i;
> LIST_HEAD(submit_list);
>
> + if (!iof && nblocks > 1) {
> + iof = iomap_iof_alloc(inode, folio, 0);
> + iomap_set_range_dirty(inode, folio, 0, folio_size(folio));
> + }
> +
> WARN_ON_ONCE(iof && atomic_read(&iof->write_bytes_pending) != 0);
>
> /*
> @@ -1662,7 +1779,7 @@ 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 (iof && !iomap_iof_is_block_uptodate(iof, i))
> + if (iof && !iomap_iof_is_block_dirty(folio, iof, i))
> continue;
>
> error = wpc->ops->map_blocks(wpc, inode, pos);
> @@ -1706,6 +1823,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> }
> }
>
> + iomap_clear_range_dirty(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
>
