Re: [PATCH v2 06/12] btrfs: make btrfs_check_nocow_lock nowait compatible

Filipe Manana
2022-09-08T10:19:09Z

On Thu, Sep 8, 2022 at 1:26 AM Stefan Roesch <shr@fb.com> wrote:
>
> From: Josef Bacik <josef@toxicpanda.com>
>
> Now all the helpers that btrfs_check_nocow_lock uses handle nowait, add
> a nowait flag to btrfs_check_nocow_lock so it can be used by the write
> path.
>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Stefan Roesch <shr@fb.com>
> ---
> fs/btrfs/ctree.h | 2 +-
> fs/btrfs/file.c | 33 ++++++++++++++++++++++-----------
> fs/btrfs/inode.c | 2 +-
> 3 files changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 536bbc8551fc..06cb25f2d3bd 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -3482,7 +3482,7 @@ int btrfs_dirty_pages(struct btrfs_inode *inode, struct page **pages,
> struct extent_state **cached, bool noreserve);
> int btrfs_fdatawrite_range(struct inode *inode, loff_t start, loff_t end);
> int btrfs_check_nocow_lock(struct btrfs_inode *inode, loff_t pos,
> - size_t *write_bytes);
> + size_t *write_bytes, bool nowait);
> void btrfs_check_nocow_unlock(struct btrfs_inode *inode);
>
> /* tree-defrag.c */
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 0f257205c63d..cf19d381ead6 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1481,7 +1481,7 @@ lock_and_cleanup_extent_if_need(struct btrfs_inode *inode, struct page **pages,
> * NOTE: Callers need to call btrfs_check_nocow_unlock() if we return > 0.
> */
> int btrfs_check_nocow_lock(struct btrfs_inode *inode, loff_t pos,
> - size_t *write_bytes)
> + size_t *write_bytes, bool nowait)
> {
> struct btrfs_fs_info *fs_info = inode->root->fs_info;
> struct btrfs_root *root = inode->root;
> @@ -1500,16 +1500,21 @@ int btrfs_check_nocow_lock(struct btrfs_inode *inode, loff_t pos,
> fs_info->sectorsize) - 1;
> num_bytes = lockend - lockstart + 1;
>
> - btrfs_lock_and_flush_ordered_range(inode, lockstart, lockend, NULL);
> + if (nowait) {
> + if (!btrfs_try_lock_ordered_range(inode, lockstart, lockend)) {
> + btrfs_drew_write_unlock(&root->snapshot_lock);
> + return -EAGAIN;
> + }
> + } else {
> + btrfs_lock_and_flush_ordered_range(inode, lockstart, lockend, NULL);
> + }
> ret = can_nocow_extent(&inode->vfs_inode, lockstart, &num_bytes,
> - NULL, NULL, NULL, false, false);
> - if (ret <= 0) {
> - ret = 0;
> + NULL, NULL, NULL, nowait, false);
> + if (ret <= 0)
> btrfs_drew_write_unlock(&root->snapshot_lock);
> - } else {
> + else
> *write_bytes = min_t(size_t, *write_bytes ,
> num_bytes - pos + lockstart);
> - }
> unlock_extent(&inode->io_tree, lockstart, lockend);
>
> return ret;
> @@ -1666,16 +1671,22 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
> &data_reserved, pos,
> write_bytes, false);
> if (ret < 0) {
> + int tmp;
> +
> /*
> * If we don't have to COW at the offset, reserve
> * metadata only. write_bytes may get smaller than
> * requested here.
> */
> - if (btrfs_check_nocow_lock(BTRFS_I(inode), pos,
> - &write_bytes) > 0)
> - only_release_metadata = true;
> - else
> + tmp = btrfs_check_nocow_lock(BTRFS_I(inode), pos,
> + &write_bytes, false);
> + if (tmp < 0)
> + ret = tmp;
> + if (tmp > 0)
> + ret = 0;
> + if (ret)

A variable named tmp is not a great name, something like "can_nocow'
would be a lot more clear.

Thanks.

> break;
> + only_release_metadata = true;
> }
>
> num_pages = DIV_ROUND_UP(write_bytes + offset, PAGE_SIZE);
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 36e755f73764..5426d4f4ac23 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -4884,7 +4884,7 @@ int btrfs_truncate_block(struct btrfs_inode *inode, loff_t from, loff_t len,
> ret = btrfs_check_data_free_space(inode, &data_reserved, block_start,
> blocksize, false);
> if (ret < 0) {
> - if (btrfs_check_nocow_lock(inode, block_start, &write_bytes) > 0) {
> + if (btrfs_check_nocow_lock(inode, block_start, &write_bytes, false) > 0) {
> /* For nocow case, no need to reserve data space */
> only_release_metadata = true;
> } else {
> --
> 2.30.2
>