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

Stefan Roesch
2022-09-08T18:23:28Z

On 9/8/22 3:18 AM, Filipe Manana wrote:
> >
> 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.
>

I renamed the variable tmp to can_nocow.

> 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
>>