On Fri, Nov 15, 2019 at 4:19 PM Goldwyn Rodrigues <rgoldwyn@xxxxxxx> wrote:
>
> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> This is the main patch to switch call from
> __blockdev_direct_IO() to iomap_dio_rw(). In this patch:
>
> Removed buffer_head references
> Removed inode_dio_begin() and inode_dio_end() functions since
> they are called in iomap_dio_rw().
> Renamed btrfs_get_blocks_direct() to direct_iomap_begin() and
> used it as iomap_begin()
> address_space.direct_IO now is a noop since direct_IO is called
> from __btrfs_write_direct().
>
> Removed flags parameter used for __blockdev_direct_IO(). iomap is
> capable of direct I/O reads from a hole, so we don't need to
> return -ENOENT.
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> ---
> fs/btrfs/ctree.h | 1 +
> fs/btrfs/file.c | 2 +-
> fs/btrfs/inode.c | 105 ++++++++++++++++++-------------------------------------
> 3 files changed, 36 insertions(+), 72 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index fe2b8765d9e6..cde8423673fc 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -2903,6 +2903,7 @@ int btrfs_writepage_cow_fixup(struct page *page, u64 start, u64 end);
> void btrfs_writepage_endio_finish_ordered(struct page *page, u64 start,
> u64 end, int uptodate);
> extern const struct dentry_operations btrfs_dentry_operations;
> +ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter);
>
> /* ioctl.c */
> long btrfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index eede9dcbb4b6..d47da00fa61e 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1835,7 +1835,7 @@ static ssize_t __btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
> loff_t endbyte;
> int err;
>
> - written = generic_file_direct_write(iocb, from);
> + written = btrfs_direct_IO(iocb, from);
>
> if (written < 0 || !iov_iter_count(from))
> return written;
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index c6dc4dd16cf7..e2e4dfb7a568 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -8,6 +8,7 @@
> #include <linux/buffer_head.h>
> #include <linux/file.h>
> #include <linux/fs.h>
> +#include <linux/iomap.h>
> #include <linux/pagemap.h>
> #include <linux/highmem.h>
> #include <linux/time.h>
> @@ -7619,28 +7620,7 @@ static struct extent_map *create_io_em(struct inode *inode, u64 start, u64 len,
> }
>
>
> -static int btrfs_get_blocks_direct_read(struct extent_map *em,
> - struct buffer_head *bh_result,
> - struct inode *inode,
> - u64 start, u64 len)
> -{
> - if (em->block_start == EXTENT_MAP_HOLE ||
> - test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
> - return -ENOENT;
> -
> - len = min(len, em->len - (start - em->start));
> -
> - bh_result->b_blocknr = (em->block_start + (start - em->start)) >>
> - inode->i_blkbits;
> - bh_result->b_size = len;
> - bh_result->b_bdev = em->bdev;
> - set_buffer_mapped(bh_result);
> -
> - return 0;
> -}
> -
> static int btrfs_get_blocks_direct_write(struct extent_map **map,
> - struct buffer_head *bh_result,
> struct inode *inode,
> struct btrfs_dio_data *dio_data,
> u64 start, u64 len)
> @@ -7702,7 +7682,6 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
> }
>
> /* this will cow the extent */
> - len = bh_result->b_size;
> free_extent_map(em);
> *map = em = btrfs_new_extent_direct(inode, start, len);
> if (IS_ERR(em)) {
> @@ -7713,15 +7692,6 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
> len = min(len, em->len - (start - em->start));
>
> skip_cow:
> - bh_result->b_blocknr = (em->block_start + (start - em->start)) >>
> - inode->i_blkbits;
> - bh_result->b_size = len;
> - bh_result->b_bdev = em->bdev;
> - set_buffer_mapped(bh_result);
> -
> - if (!test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
> - set_buffer_new(bh_result);
> -
> /*
> * Need to update the i_size under the extent lock so buffered
> * readers will get the updated i_size when we unlock.
> @@ -7737,17 +7707,18 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,
> return ret;
> }
>
> -static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> - struct buffer_head *bh_result, int create)
> +static int direct_iomap_begin(struct inode *inode, loff_t start,
> + loff_t length, unsigned flags, struct iomap *iomap,
> + struct iomap *srcmap)
> {
> struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> struct extent_map *em;
> struct extent_state *cached_state = NULL;
> struct btrfs_dio_data *dio_data = NULL;
> - u64 start = iblock << inode->i_blkbits;
> u64 lockstart, lockend;
> - u64 len = bh_result->b_size;
> + int create = flags & IOMAP_WRITE;
> int ret = 0;
> + u64 len = length;
>
> if (!create)
> len = min_t(u64, len, fs_info->sectorsize);
> @@ -7803,7 +7774,7 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> }
>
> if (create) {
> - ret = btrfs_get_blocks_direct_write(&em, bh_result, inode,
> + ret = btrfs_get_blocks_direct_write(&em, inode,
> dio_data, start, len);
> if (ret < 0)
> goto unlock_err;
> @@ -7811,19 +7782,13 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart,
> lockend, &cached_state);
> } else {
> - ret = btrfs_get_blocks_direct_read(em, bh_result, inode,
> - start, len);
> - /* Can be negative only if we read from a hole */
> - if (ret < 0) {
> - ret = 0;
> - free_extent_map(em);
> - goto unlock_err;
> - }
> +
> + len = min(len, em->len - (start - em->start));
> /*
> * We need to unlock only the end area that we aren't using.
> * The rest is going to be unlocked by the endio routine.
> */
> - lockstart = start + bh_result->b_size;
> + lockstart = start + len;
> if (lockstart < lockend) {
> unlock_extent_cached(&BTRFS_I(inode)->io_tree,
> lockstart, lockend, &cached_state);
> @@ -7832,6 +7797,18 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> }
> }
>
> + if ((em->block_start == EXTENT_MAP_HOLE) ||
> + (test_bit(EXTENT_FLAG_PREALLOC, &em->flags) && !create)) {
> + iomap->addr = IOMAP_NULL_ADDR;
> + iomap->type = IOMAP_HOLE;
> + } else {
> + iomap->addr = em->block_start - (start - em->start);
> + iomap->type = IOMAP_MAPPED;
> + }
> + iomap->offset = start;
> + iomap->bdev = em->bdev;
> + iomap->length = min(len, em->len - (start - em->start));
> +
> free_extent_map(em);
>
> return 0;
> @@ -8199,9 +8176,8 @@ static void btrfs_endio_direct_read(struct bio *bio)
> kfree(dip);
>
> dio_bio->bi_status = err;
> - dio_end_io(dio_bio);
> + bio_endio(dio_bio);
> btrfs_io_bio_free_csum(io_bio);
> - bio_put(bio);
> }
>
> static void __endio_write_update_ordered(struct inode *inode,
> @@ -8263,8 +8239,7 @@ static void btrfs_endio_direct_write(struct bio *bio)
> kfree(dip);
>
> dio_bio->bi_status = bio->bi_status;
> - dio_end_io(dio_bio);
> - bio_put(bio);
> + bio_endio(dio_bio);
> }
>
> static blk_status_t btrfs_submit_bio_start_direct_io(void *private_data,
> @@ -8568,7 +8543,7 @@ static void btrfs_submit_direct(struct bio *dio_bio, struct inode *inode,
> /*
> * The end io callbacks free our dip, do the final put on bio
> * and all the cleanup and final put for dio_bio (through
> - * dio_end_io()).
> + * end_io()).
> */
> dip = NULL;
> bio = NULL;
> @@ -8587,7 +8562,7 @@ static void btrfs_submit_direct(struct bio *dio_bio, struct inode *inode,
> * Releases and cleans up our dio_bio, no need to bio_put()
> * nor bio_endio()/bio_io_error() against dio_bio.
> */
> - dio_end_io(dio_bio);
> + bio_endio(dio_bio);
The comment above also needs to be updated. It explicitly mentions
there's no need to call bio_endio(), but now the code it's calling
that function.
> }
> if (bio)
> bio_put(bio);
> @@ -8627,7 +8602,11 @@ static ssize_t check_direct_IO(struct btrfs_fs_info *fs_info,
> return retval;
> }
>
> -static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> +static const struct iomap_ops dio_iomap_ops = {
> + .iomap_begin = direct_iomap_begin,
> +};
> +
> +ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> {
> struct file *file = iocb->ki_filp;
> struct inode *inode = file->f_mapping->host;
> @@ -8637,14 +8616,11 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> loff_t offset = iocb->ki_pos;
> size_t count = 0;
> int flags = 0;
> - bool wakeup = true;
> - bool relock = false;
> ssize_t ret;
>
> if (check_direct_IO(fs_info, iter, offset))
> return 0;
>
> - inode_dio_begin(inode);
>
> /*
> * The generic stuff only does filemap_write_and_wait_range, which
> @@ -8664,11 +8640,7 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> * the isize, but it is protected by i_mutex. So we can
> * not unlock the i_mutex at this case.
> */
> - if (offset + count <= inode->i_size) {
> - dio_data.overwrite = 1;
> - inode_unlock(inode);
> - relock = true;
I'm not familiar with iomap, but a quick grep at iomap/*.c (5.4-rc7)
reveals no call to inode_unlock().
So this change is throwing away the optimization done by commit [1],
which makes a lot of sense and when it landed I observed as well that
it made a great difference (as expected).
Correct me if I'm wrong, but that optimization is now gone isn't it?
So concurrent direct IO writes to a file, that don't expand the
inode's i_size and operate on non-overlapping ranges, will now be
completely serialized.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=38851cc19adbfa1def2b47106d8050a80e0a3673
Thanks
> - } else if (iocb->ki_flags & IOCB_NOWAIT) {
> + if (iocb->ki_flags & IOCB_NOWAIT) {
> ret = -EAGAIN;
> goto out;
> }
> @@ -8690,15 +8662,11 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> down_read(&BTRFS_I(inode)->dio_sem);
> } else if (test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
> &BTRFS_I(inode)->runtime_flags)) {
> - inode_dio_end(inode);
> flags = DIO_LOCKING | DIO_SKIP_HOLES;
> - wakeup = false;
> }
>
> - ret = __blockdev_direct_IO(iocb, inode,
> - fs_info->fs_devices->latest_bdev,
> - iter, btrfs_get_blocks_direct, NULL,
> - btrfs_submit_direct, flags);
> + ret = iomap_dio_rw(iocb, iter, &dio_iomap_ops, NULL, is_sync_kiocb(iocb));
> +
> if (iov_iter_rw(iter) == WRITE) {
> up_read(&BTRFS_I(inode)->dio_sem);
> current->journal_info = NULL;
> @@ -8725,11 +8693,6 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> btrfs_delalloc_release_extents(BTRFS_I(inode), count);
> }
> out:
> - if (wakeup)
> - inode_dio_end(inode);
> - if (relock)
> - inode_lock(inode);
> -
> extent_changeset_free(data_reserved);
> return ret;
> }
> --
> 2.16.4
>
--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
