Re: [RFC PATCH v2 5/5] btrfs: implement RWF_ENCODED writes

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On 15.10.19 г. 21:42 ч., Omar Sandoval wrote:
> From: Omar Sandoval <osandov@xxxxxx>
> 
> The implementation resembles direct I/O: we have to flush any ordered
> extents, invalidate the page cache, and do the io tree/delalloc/extent
> map/ordered extent dance. From there, we can reuse the compression code
> with a minor modification to distinguish the write from writeback.
> 
> Now that read and write are implemented, this also sets the
> FMODE_ENCODED_IO flag in btrfs_file_open().
> 
> Signed-off-by: Omar Sandoval <osandov@xxxxxx>
> ---
>  fs/btrfs/compression.c |   6 +-
>  fs/btrfs/compression.h |   5 +-
>  fs/btrfs/ctree.h       |   2 +
>  fs/btrfs/file.c        |  40 +++++++--
>  fs/btrfs/inode.c       | 197 ++++++++++++++++++++++++++++++++++++++++-
>  5 files changed, 237 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
> index b05b361e2062..6632dd8d2e4d 100644
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -276,7 +276,8 @@ static void end_compressed_bio_write(struct bio *bio)
>  			bio->bi_status == BLK_STS_OK);
>  	cb->compressed_pages[0]->mapping = NULL;
>  
> -	end_compressed_writeback(inode, cb);
> +	if (cb->writeback)
> +		end_compressed_writeback(inode, cb);
>  	/* note, our inode could be gone now */
>  
>  	/*
> @@ -311,7 +312,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
>  				 unsigned long compressed_len,
>  				 struct page **compressed_pages,
>  				 unsigned long nr_pages,
> -				 unsigned int write_flags)
> +				 unsigned int write_flags, bool writeback)

I don't see this function being called with true in this patch set,
meaning it essentially eliminates end_compressed_writeback call in
end_compressed_bio_write? Am I missing anything?

>  {
>  	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
>  	struct bio *bio = NULL;
> @@ -336,6 +337,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
>  	cb->mirror_num = 0;
>  	cb->compressed_pages = compressed_pages;
>  	cb->compressed_len = compressed_len;
> +	cb->writeback = writeback;
>  	cb->orig_bio = NULL;
>  	cb->nr_pages = nr_pages;
>  
> diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
> index 4cb8be9ff88b..d4176384ec15 100644
> --- a/fs/btrfs/compression.h
> +++ b/fs/btrfs/compression.h
> @@ -47,6 +47,9 @@ struct compressed_bio {
>  	/* the compression algorithm for this bio */
>  	int compress_type;
>  
> +	/* Whether this is a write for writeback. */
> +	bool writeback;
> +
>  	/* number of compressed pages in the array */
>  	unsigned long nr_pages;
>  
> @@ -93,7 +96,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
>  				  unsigned long compressed_len,
>  				  struct page **compressed_pages,
>  				  unsigned long nr_pages,
> -				  unsigned int write_flags);
> +				  unsigned int write_flags, bool writeback);
>  blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
>  				 int mirror_num, unsigned long bio_flags);
>  
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 3b2aa1c7218c..9e1719e82cc8 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -2907,6 +2907,8 @@ 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);
>  ssize_t btrfs_encoded_read(struct kiocb *iocb, struct iov_iter *iter);
> +ssize_t btrfs_encoded_write(struct kiocb *iocb, struct iov_iter *from,
> +			    struct encoded_iov *encoded);
>  
>  extern const struct dentry_operations btrfs_dentry_operations;
>  
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 51740cee39fc..8de6ac9b4b9c 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1893,8 +1893,7 @@ static void update_time_for_write(struct inode *inode)
>  		inode_inc_iversion(inode);
>  }
>  
> -static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> -				    struct iov_iter *from)
> +static ssize_t btrfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  {
>  	struct file *file = iocb->ki_filp;
>  	struct inode *inode = file_inode(file);
> @@ -1904,14 +1903,22 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
>  	u64 end_pos;
>  	ssize_t num_written = 0;
>  	const bool sync = iocb->ki_flags & IOCB_DSYNC;
> +	struct encoded_iov encoded;
>  	ssize_t err;
>  	loff_t pos;
>  	size_t count;
>  	loff_t oldsize;
>  	int clean_page = 0;
>  
> -	if (!(iocb->ki_flags & IOCB_DIRECT) &&
> -	    (iocb->ki_flags & IOCB_NOWAIT))
> +	if (iocb->ki_flags & IOCB_ENCODED) {
> +		err = import_encoded_write(iocb, &encoded, from);
> +		if (err)
> +			return err;
> +	}
> +
> +	if ((iocb->ki_flags & IOCB_NOWAIT) &&
> +	    (!(iocb->ki_flags & IOCB_DIRECT) ||
> +	     (iocb->ki_flags & IOCB_ENCODED)))
>  		return -EOPNOTSUPP;
>  
>  	if (!inode_trylock(inode)) {
> @@ -1920,14 +1927,27 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
>  		inode_lock(inode);
>  	}
>  
> -	err = generic_write_checks(iocb, from);
> -	if (err <= 0) {
> +	if (iocb->ki_flags & IOCB_ENCODED) {
> +		err = generic_encoded_write_checks(iocb, &encoded);
> +		if (err) {
> +			inode_unlock(inode);
> +			return err;
> +		}
> +		count = encoded.len;
> +	} else {
> +		err = generic_write_checks(iocb, from);
> +		if (err < 0) {
> +			inode_unlock(inode);
> +			return err;
> +		}
> +		count = iov_iter_count(from);
> +	}
> +	if (count == 0) {
>  		inode_unlock(inode);
>  		return err;
>  	}
>  
>  	pos = iocb->ki_pos;
> -	count = iov_iter_count(from);
>  	if (iocb->ki_flags & IOCB_NOWAIT) {
>  		/*
>  		 * We will allocate space in case nodatacow is not set,
> @@ -1986,7 +2006,9 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
>  	if (sync)
>  		atomic_inc(&BTRFS_I(inode)->sync_writers);
>  
> -	if (iocb->ki_flags & IOCB_DIRECT) {
> +	if (iocb->ki_flags & IOCB_ENCODED) {
> +		num_written = btrfs_encoded_write(iocb, from, &encoded);
> +	} else if (iocb->ki_flags & IOCB_DIRECT) {
>  		num_written = __btrfs_direct_write(iocb, from);
>  	} else {
>  		num_written = btrfs_buffered_write(iocb, from);
> @@ -3461,7 +3483,7 @@ static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int whence)
>  
>  static int btrfs_file_open(struct inode *inode, struct file *filp)
>  {
> -	filp->f_mode |= FMODE_NOWAIT;
> +	filp->f_mode |= FMODE_NOWAIT | FMODE_ENCODED_IO;
>  	return generic_file_open(inode, filp);
>  }
>  
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 174d0738d2c9..bcc5a2bed22b 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -865,7 +865,7 @@ static noinline void submit_compressed_extents(struct async_chunk *async_chunk)
>  				    ins.objectid,
>  				    ins.offset, async_extent->pages,
>  				    async_extent->nr_pages,
> -				    async_chunk->write_flags)) {
> +				    async_chunk->write_flags, true)) {
>  			struct page *p = async_extent->pages[0];
>  			const u64 start = async_extent->start;
>  			const u64 end = start + async_extent->ram_size - 1;
> @@ -11055,6 +11055,201 @@ ssize_t btrfs_encoded_read(struct kiocb *iocb, struct iov_iter *iter)
>  	return ret;
>  }
>  
> +ssize_t btrfs_encoded_write(struct kiocb *iocb, struct iov_iter *from,
> +			    struct encoded_iov *encoded)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> +	struct btrfs_root *root = BTRFS_I(inode)->root;
> +	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
> +	struct extent_changeset *data_reserved = NULL;
> +	struct extent_state *cached_state = NULL;
> +	int compression;
> +	size_t orig_count;
> +	u64 disk_num_bytes, num_bytes;
> +	u64 start, end;
> +	unsigned long nr_pages, i;
> +	struct page **pages;
> +	struct btrfs_key ins;
> +	struct extent_map *em;
> +	ssize_t ret;
> +
> +	switch (encoded->compression) {
> +	case ENCODED_IOV_COMPRESSION_ZLIB:
> +		compression = BTRFS_COMPRESS_ZLIB;
> +		break;
> +	case ENCODED_IOV_COMPRESSION_LZO:
> +		compression = BTRFS_COMPRESS_LZO;
> +		break;
> +	case ENCODED_IOV_COMPRESSION_ZSTD:
> +		compression = BTRFS_COMPRESS_ZSTD;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	disk_num_bytes = orig_count = iov_iter_count(from);
> +
> +	/* For now, it's too hard to support bookend extents. */
> +	if (encoded->unencoded_len != encoded->len ||
> +	    encoded->unencoded_offset != 0)
> +		return -EINVAL;
> +
> +	/* The extent size must be sane. */
> +	if (encoded->unencoded_len > BTRFS_MAX_UNCOMPRESSED ||
> +	    disk_num_bytes > BTRFS_MAX_COMPRESSED || disk_num_bytes == 0)
> +		return -EINVAL;
> +
> +	/*
> +	 * The compressed data on disk must be sector-aligned. For convenience,
> +	 * we extend it with zeroes if it isn't.
> +	 */
> +	disk_num_bytes = ALIGN(disk_num_bytes, fs_info->sectorsize);
> +
> +	/*
> +	 * The extent in the file must also be sector-aligned. However, we allow
> +	 * a write which ends at or extends i_size to have an unaligned length;
> +	 * we round up the extent size and set i_size to the given length.
> +	 */
> +	start = iocb->ki_pos;
> +	if (!IS_ALIGNED(start, fs_info->sectorsize))
> +		return -EINVAL;
> +	if (start + encoded->len >= inode->i_size) {
> +		num_bytes = ALIGN(encoded->len, fs_info->sectorsize);
> +	} else {
> +		num_bytes = encoded->len;
> +		if (!IS_ALIGNED(num_bytes, fs_info->sectorsize))
> +			return -EINVAL;
> +	}
> +
> +	/*
> +	 * It's valid to have compressed data which is larger than or the same
> +	 * size as the decompressed data. However, for buffered I/O, we fall
> +	 * back to writing the decompressed data if compression didn't shrink
> +	 * it. So, for now, let's not allow creating such extents.
> +	 *
> +	 * Note that for now this also implicitly prevents writing data that
> +	 * would fit in an inline extent.
> +	 */
> +	if (disk_num_bytes >= num_bytes)
> +		return -EINVAL;
> +
> +	end = start + num_bytes - 1;
> +
> +	nr_pages = (disk_num_bytes + PAGE_SIZE - 1) >> PAGE_SHIFT;

nit: nr_pages = DIV_ROUND_UP(disk_num_bytes, PAGE_SIZE)

> +	pages = kvcalloc(nr_pages, sizeof(struct page *), GFP_USER);

This could be a simple GFP_KERNEL  allocation

> +	if (!pages)
> +		return -ENOMEM;
> +	for (i = 0; i < nr_pages; i++) {
> +		size_t bytes = min_t(size_t, PAGE_SIZE, iov_iter_count(from));
> +		char *kaddr;
> +
> +		pages[i] = alloc_page(GFP_HIGHUSER);

Why GFP_HIGHUSER? You are reading from userspace,  not writing to it. A
plain, NOFS allocation should suffice (of course using the newer
memalloc_nofs_save api)?


> +		if (!pages[i]) {
> +			ret = -ENOMEM;
> +			goto out_pages;
> +		}
> +		kaddr = kmap(pages[i]);
> +		if (copy_from_iter(kaddr, bytes, from) != bytes) {
> +			kunmap(pages[i]);
> +			ret = -EFAULT;
> +			goto out_pages;
> +		}
> +		if (bytes < PAGE_SIZE)
> +			memset(kaddr + bytes, 0, PAGE_SIZE - bytes);
> +		kunmap(pages[i]);
> +	}
> +
> +	for (;;) {
> +		struct btrfs_ordered_extent *ordered;
> +
> +		ret = btrfs_wait_ordered_range(inode, start, end - start + 1);
> +		if (ret)
> +			goto out_pages;
> +		ret = invalidate_inode_pages2_range(inode->i_mapping,
> +						    start >> PAGE_SHIFT,
> +						    end >> PAGE_SHIFT);
> +		if (ret)
> +			goto out_pages;
> +		lock_extent_bits(io_tree, start, end, &cached_state);
> +		ordered = btrfs_lookup_ordered_range(BTRFS_I(inode), start,
> +						     end - start + 1);
> +		if (!ordered &&
> +		    !filemap_range_has_page(inode->i_mapping, start, end))
> +			break;
> +		if (ordered)
> +			btrfs_put_ordered_extent(ordered);
> +		unlock_extent_cached(io_tree, start, end, &cached_state);
> +		cond_resched();
> +	}
> +
> +	ret = btrfs_delalloc_reserve_space(inode, &data_reserved, start,
> +					   num_bytes);
> +	if (ret)
> +		goto out_unlock;
> +
> +	ret = btrfs_reserve_extent(root, num_bytes, disk_num_bytes,
> +				   disk_num_bytes, 0, 0, &ins, 1, 1);
> +	if (ret)
> +		goto out_delalloc_release;
> +
> +	em = create_io_em(inode, start, num_bytes, start, ins.objectid,
> +			  ins.offset, ins.offset, num_bytes, compression,
> +			  BTRFS_ORDERED_COMPRESSED);
> +	if (IS_ERR(em)) {
> +		ret = PTR_ERR(em);
> +		goto out_free_reserve;
> +	}
> +	free_extent_map(em);
> +
> +	ret = btrfs_add_ordered_extent_compress(inode, start, ins.objectid,
> +						num_bytes, ins.offset,
> +						BTRFS_ORDERED_COMPRESSED,
> +						compression);
> +	if (ret) {
> +		btrfs_drop_extent_cache(BTRFS_I(inode), start, end, 0);
> +		goto out_free_reserve;
> +	}
> +	btrfs_dec_block_group_reservations(fs_info, ins.objectid);
> +
> +	if (start + encoded->len > inode->i_size)
> +		i_size_write(inode, start + encoded->len);

Don't we want the inode size to be updated once data hits disk and
btrfs_finish_ordered_io is called?

> +
> +	unlock_extent_cached(io_tree, start, end, &cached_state);
> +
> +	btrfs_delalloc_release_extents(BTRFS_I(inode), num_bytes, false);
> +
> +	if (btrfs_submit_compressed_write(inode, start, num_bytes, ins.objectid,
> +					  ins.offset, pages, nr_pages, 0,
> +					  false)) {
> +		struct page *page = pages[0];
> +
> +		page->mapping = inode->i_mapping;
> +		btrfs_writepage_endio_finish_ordered(page, start, end, 0);
> +		page->mapping = NULL;
> +		ret = -EIO;
> +		goto out_pages;
> +	}
> +	iocb->ki_pos += encoded->len;
> +	return orig_count;
> +
> +out_free_reserve:
> +	btrfs_dec_block_group_reservations(fs_info, ins.objectid);
> +	btrfs_free_reserved_extent(fs_info, ins.objectid, ins.offset, 1);
> +out_delalloc_release:
> +	btrfs_delalloc_release_space(inode, data_reserved, start, num_bytes,
> +				     true);
> +out_unlock:
> +	unlock_extent_cached(io_tree, start, end, &cached_state);
> +out_pages:
> +	for (i = 0; i < nr_pages; i++) {
> +		if (pages[i])
> +			put_page(pages[i]);
> +	}
> +	kvfree(pages);
> +	return ret;
> +}
> +
>  #ifdef CONFIG_SWAP
>  /*
>   * Add an entry indicating a block group or device which is pinned by a
> 



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