On Thu, Dec 19, 2024 at 05:39:09PM +0000, Christoph Hellwig wrote:
> Provide helpers for file systems to split bios in the direct I/O and
> writeback I/O submission handlers.
>
> This Follows btrfs' lead and don't try to build bios to hardware limits
> for zone append commands, but instead build them as normal unconstrained
> bios and split them to the hardware limits in the I/O submission handler.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
I wonder what iomap_split_ioend callsites look like now that the
alloc_len outparam from the previous version is gone, but I guess I'll
have to wait to see that.
> ---
> fs/iomap/Makefile | 1 +
> fs/iomap/buffered-io.c | 49 ++++++++++++++----------
> fs/iomap/ioend.c | 86 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/iomap.h | 9 +++++
> 4 files changed, 125 insertions(+), 20 deletions(-)
> create mode 100644 fs/iomap/ioend.c
>
> diff --git a/fs/iomap/Makefile b/fs/iomap/Makefile
> index 381d76c5c232..69e8ebb41302 100644
> --- a/fs/iomap/Makefile
> +++ b/fs/iomap/Makefile
> @@ -12,6 +12,7 @@ iomap-y += trace.o \
> iter.o
> iomap-$(CONFIG_BLOCK) += buffered-io.o \
> direct-io.o \
> + ioend.o \
> fiemap.o \
> seek.o
> iomap-$(CONFIG_SWAP) += swapfile.o
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 8c18fb2a82e0..0b68c9584a7f 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -40,7 +40,8 @@ struct iomap_folio_state {
> unsigned long state[];
> };
>
> -static struct bio_set iomap_ioend_bioset;
> +struct bio_set iomap_ioend_bioset;
> +EXPORT_SYMBOL_GPL(iomap_ioend_bioset);
>
> static inline bool ifs_is_fully_uptodate(struct folio *folio,
> struct iomap_folio_state *ifs)
> @@ -1539,15 +1540,15 @@ static void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
> * ioend after this.
> */
> static u32
> -iomap_finish_ioend(struct iomap_ioend *ioend, int error)
> +iomap_finish_ioend_buffered(struct iomap_ioend *ioend)
> {
> struct inode *inode = ioend->io_inode;
> struct bio *bio = &ioend->io_bio;
> struct folio_iter fi;
> u32 folio_count = 0;
>
> - if (error) {
> - mapping_set_error(inode->i_mapping, error);
> + if (ioend->io_error) {
> + mapping_set_error(inode->i_mapping, ioend->io_error);
> if (!bio_flagged(bio, BIO_QUIET)) {
> pr_err_ratelimited(
> "%s: writeback error on inode %lu, offset %lld, sector %llu",
> @@ -1566,6 +1567,24 @@ iomap_finish_ioend(struct iomap_ioend *ioend, int error)
> return folio_count;
> }
>
> +static u32
> +iomap_finish_ioend(struct iomap_ioend *ioend, int error)
> +{
> + if (ioend->io_parent) {
> + struct bio *bio = &ioend->io_bio;
> +
> + ioend = ioend->io_parent;
> + bio_put(bio);
> + }
> +
> + if (error)
> + cmpxchg(&ioend->io_error, 0, error);
> +
> + if (!atomic_dec_and_test(&ioend->io_remaining))
> + return 0;
> + return iomap_finish_ioend_buffered(ioend);
> +}
> +
> /*
> * Ioend completion routine for merged bios. This can only be called from task
> * contexts as merged ioends can be of unbound length. Hence we have to break up
> @@ -1667,8 +1686,10 @@ EXPORT_SYMBOL_GPL(iomap_sort_ioends);
>
> static void iomap_writepage_end_bio(struct bio *bio)
> {
> - iomap_finish_ioend(iomap_ioend_from_bio(bio),
> - blk_status_to_errno(bio->bi_status));
> + struct iomap_ioend *ioend = iomap_ioend_from_bio(bio);
> +
> + ioend->io_error = blk_status_to_errno(bio->bi_status);
> + iomap_finish_ioend_buffered(ioend);
Hmm. This wasn't in the previous version of the patch. But my guess is
that anyone using the io_parent chaining has its own ->submit_ioend
function and therefore set its own bi_end_io function? IOWs, letting
iomap submit the bio itself is not compatible with io_parent != NULL.
If so, then you might want to note that in the declaration of io_parent
in iomap.h; and with that,
Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
--D
> }
>
> /*
> @@ -1713,7 +1734,6 @@ static struct iomap_ioend *iomap_alloc_ioend(struct iomap_writepage_ctx *wpc,
> struct writeback_control *wbc, struct inode *inode, loff_t pos,
> u16 ioend_flags)
> {
> - struct iomap_ioend *ioend;
> struct bio *bio;
>
> bio = bio_alloc_bioset(wpc->iomap.bdev, BIO_MAX_VECS,
> @@ -1721,21 +1741,10 @@ static struct iomap_ioend *iomap_alloc_ioend(struct iomap_writepage_ctx *wpc,
> GFP_NOFS, &iomap_ioend_bioset);
> bio->bi_iter.bi_sector = iomap_sector(&wpc->iomap, pos);
> bio->bi_end_io = iomap_writepage_end_bio;
> - wbc_init_bio(wbc, bio);
> bio->bi_write_hint = inode->i_write_hint;
> -
> - ioend = iomap_ioend_from_bio(bio);
> - INIT_LIST_HEAD(&ioend->io_list);
> - ioend->io_flags = ioend_flags;
> - if (pos > wpc->iomap.offset)
> - wpc->iomap.flags &= ~IOMAP_F_BOUNDARY;
> - ioend->io_inode = inode;
> - ioend->io_size = 0;
> - ioend->io_offset = pos;
> - ioend->io_sector = bio->bi_iter.bi_sector;
> -
> + wbc_init_bio(wbc, bio);
> wpc->nr_folios = 0;
> - return ioend;
> + return iomap_init_ioend(inode, bio, pos, ioend_flags);
> }
>
> static bool iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t pos,
> diff --git a/fs/iomap/ioend.c b/fs/iomap/ioend.c
> new file mode 100644
> index 000000000000..1b032323ee4e
> --- /dev/null
> +++ b/fs/iomap/ioend.c
> @@ -0,0 +1,86 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2024 Christoph Hellwig.
> + */
> +#include <linux/iomap.h>
> +
> +struct iomap_ioend *iomap_init_ioend(struct inode *inode,
> + struct bio *bio, loff_t file_offset, u16 ioend_flags)
> +{
> + struct iomap_ioend *ioend = iomap_ioend_from_bio(bio);
> +
> + atomic_set(&ioend->io_remaining, 1);
> + ioend->io_error = 0;
> + ioend->io_parent = NULL;
> + INIT_LIST_HEAD(&ioend->io_list);
> + ioend->io_flags = ioend_flags;
> + ioend->io_inode = inode;
> + ioend->io_offset = file_offset;
> + ioend->io_size = bio->bi_iter.bi_size;
> + ioend->io_sector = bio->bi_iter.bi_sector;
> + return ioend;
> +}
> +EXPORT_SYMBOL_GPL(iomap_init_ioend);
> +
> +/*
> + * Split up to the first @max_len bytes from @ioend if the ioend covers more
> + * than @max_len bytes.
> + *
> + * If @is_append is set, the split will be based on the hardware limits for
> + * REQ_OP_ZONE_APPEND commands and can be less than @max_len if the hardware
> + * limits don't allow the entire @max_len length.
> + *
> + * The bio embedded into @ioend must be a REQ_OP_WRITE because the block layer
> + * does not allow splitting REQ_OP_ZONE_APPEND bios. The file systems has to
> + * switch the operation after this call, but before submitting the bio.
> + */
> +struct iomap_ioend *iomap_split_ioend(struct iomap_ioend *ioend,
> + unsigned int max_len, bool is_append)
> +{
> + struct bio *bio = &ioend->io_bio;
> + struct iomap_ioend *split_ioend;
> + unsigned int nr_segs;
> + int sector_offset;
> + struct bio *split;
> +
> + if (is_append) {
> + struct queue_limits *lim = bdev_limits(bio->bi_bdev);
> +
> + max_len = min(max_len,
> + lim->max_zone_append_sectors << SECTOR_SHIFT);
> +
> + sector_offset = bio_split_rw_at(bio, lim, &nr_segs, max_len);
> + if (unlikely(sector_offset < 0))
> + return ERR_PTR(sector_offset);
> + if (!sector_offset)
> + return NULL;
> + } else {
> + if (bio->bi_iter.bi_size <= max_len)
> + return NULL;
> + sector_offset = max_len >> SECTOR_SHIFT;
> + }
> +
> + /* ensure the split ioend is still block size aligned */
> + sector_offset = ALIGN_DOWN(sector_offset << SECTOR_SHIFT,
> + i_blocksize(ioend->io_inode)) >> SECTOR_SHIFT;
> +
> + split = bio_split(bio, sector_offset, GFP_NOFS, &iomap_ioend_bioset);
> + if (IS_ERR_OR_NULL(split))
> + return ERR_CAST(split);
> + split->bi_private = bio->bi_private;
> + split->bi_end_io = bio->bi_end_io;
> +
> + split_ioend = iomap_init_ioend(ioend->io_inode, split, ioend->io_offset,
> + ioend->io_flags);
> + split_ioend->io_parent = ioend;
> +
> + atomic_inc(&ioend->io_remaining);
> + ioend->io_offset += split_ioend->io_size;
> + ioend->io_size -= split_ioend->io_size;
> +
> + split_ioend->io_sector = ioend->io_sector;
> + if (!is_append)
> + ioend->io_sector += (split_ioend->io_size >> SECTOR_SHIFT);
> + return split_ioend;
> +}
> +EXPORT_SYMBOL_GPL(iomap_split_ioend);
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 36a7298b6cea..0d221fbe0eb3 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -358,6 +358,9 @@ struct iomap_ioend {
> struct list_head io_list; /* next ioend in chain */
> u16 io_flags; /* IOMAP_IOEND_* */
> struct inode *io_inode; /* file being written to */
> + atomic_t io_remaining; /* completetion defer count */
> + int io_error; /* stashed away status */
> + struct iomap_ioend *io_parent; /* parent for completions */
> size_t io_size; /* size of the extent */
> loff_t io_offset; /* offset in the file */
> sector_t io_sector; /* start sector of ioend */
> @@ -408,6 +411,10 @@ struct iomap_writepage_ctx {
> u32 nr_folios; /* folios added to the ioend */
> };
>
> +struct iomap_ioend *iomap_init_ioend(struct inode *inode, struct bio *bio,
> + loff_t file_offset, u16 ioend_flags);
> +struct iomap_ioend *iomap_split_ioend(struct iomap_ioend *ioend,
> + unsigned int max_len, bool is_append);
> void iomap_finish_ioends(struct iomap_ioend *ioend, int error);
> void iomap_ioend_try_merge(struct iomap_ioend *ioend,
> struct list_head *more_ioends);
> @@ -479,4 +486,6 @@ int iomap_swapfile_activate(struct swap_info_struct *sis,
> # define iomap_swapfile_activate(sis, swapfile, pagespan, ops) (-EIO)
> #endif /* CONFIG_SWAP */
>
> +extern struct bio_set iomap_ioend_bioset;
> +
> #endif /* LINUX_IOMAP_H */
> --
> 2.45.2
>
>
