Re: [RFC PATCH] iomap: generalize IOMAP_INLINE to cover tail-packing case

[Chao Yu <yuchao0@huawei.com>]

On 2019/7/11 20:28, Andreas Gruenbacher wrote:
> Something along the lines of the attached, broken patch might work in
> the end.
> 
> Andreas
> 
> ---
>  fs/buffer.c           | 10 ++++--
>  fs/iomap.c            | 74 +++++++++++++++++++++++++++++--------------
>  include/linux/iomap.h |  3 ++
>  3 files changed, 61 insertions(+), 26 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index e450c55f6434..8d8668e377ab 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1873,8 +1873,8 @@ void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
>  EXPORT_SYMBOL(page_zero_new_buffers);
>  
>  static void
> -iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
> -		struct iomap *iomap)
> +iomap_to_bh(struct inode *inode, struct page *page, sector_t block,
> +		struct buffer_head *bh, struct iomap *iomap)
>  {
>  	loff_t offset = block << inode->i_blkbits;
>  
> @@ -1924,6 +1924,10 @@ iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
>  				inode->i_blkbits;
>  		set_buffer_mapped(bh);
>  		break;
> +	case IOMAP_INLINE:
> +		__iomap_read_inline_data(inode, page, iomap);
> +		set_buffer_uptodate(bh);
> +		break;
>  	}
>  }
>  
> @@ -1969,7 +1973,7 @@ int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
>  				if (err)
>  					break;
>  			} else {
> -				iomap_to_bh(inode, block, bh, iomap);
> +				iomap_to_bh(inode, page, block, bh, iomap);
>  			}
>  
>  			if (buffer_new(bh)) {
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 45aa58e837b5..61188e95def2 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -260,24 +260,47 @@ struct iomap_readpage_ctx {
>  	struct list_head	*pages;
>  };
>  
> -static void
> -iomap_read_inline_data(struct inode *inode, struct page *page,
> +#define offset_in_block(offset, inode) \
> +	((unsigned long)(offset) & (i_blocksize(inode) - 1))
> +
> +static bool
> +inline_data_within_block(struct inode *inode, struct iomap *iomap,
> +		unsigned int size)
> +{
> +	unsigned int off = offset_in_block(iomap->inline_data, inode);
> +
> +	return size <= i_blocksize(inode) - off;
> +}
> +
> +void
> +__iomap_read_inline_data(struct inode *inode, struct page *page,
>  		struct iomap *iomap)
>  {
> -	size_t size = i_size_read(inode);
> +	size_t size = offset_in_block(i_size_read(inode), inode);
> +	unsigned int poff = offset_in_page(iomap->offset);
> +	unsigned int bsize = i_blocksize(inode);
>  	void *addr;
>  
>  	if (PageUptodate(page))
>  		return;
>  
> -	BUG_ON(page->index);
> -	BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
> +	BUG_ON(!inline_data_within_block(inode, iomap, size));
>  
>  	addr = kmap_atomic(page);
> -	memcpy(addr, iomap->inline_data, size);
> -	memset(addr + size, 0, PAGE_SIZE - size);
> +	memcpy(addr + poff, iomap->inline_data, size);
> +	memset(addr + poff + size, 0, bsize - size);
>  	kunmap_atomic(addr);
> -	SetPageUptodate(page);
> +}
> +
> +static void
> +iomap_read_inline_data(struct inode *inode, struct page *page,
> +		struct iomap *iomap)
> +{
> +	unsigned int poff = offset_in_page(iomap->offset);
> +	unsigned int bsize = i_blocksize(inode);
> +
> +	__iomap_read_inline_data(inode, page, iomap);
> +	iomap_set_range_uptodate(page, poff, bsize);
>  }
>  
>  static loff_t
> @@ -292,11 +315,8 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>  	unsigned poff, plen;
>  	sector_t sector;
>  
> -	if (iomap->type == IOMAP_INLINE) {
> -		WARN_ON_ONCE(pos);
> +	if (iomap->type == IOMAP_INLINE)
>  		iomap_read_inline_data(inode, page, iomap);
> -		return PAGE_SIZE;

Hi Andreas,

Thanks for your patch.

In my erofs test case, filled inline data will be zeroed out due to we fallback
to following flow:

	if (iomap->type != IOMAP_MAPPED || pos >= i_size_read(inode)) {
		zero_user(page, poff, plen);

Should we return before this condition check?

Thanks,

> -	}
>  
>  	/* zero post-eof blocks as the page may be mapped */
>  	iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
> @@ -637,6 +657,11 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len,
>  	if (PageUptodate(page))
>  		return 0;
>  
> +	if (iomap->type == IOMAP_INLINE) {
> +		iomap_read_inline_data(inode, page, iomap);
> +		return 0;
> +	}
> +
>  	do {
>  		iomap_adjust_read_range(inode, iop, &block_start,
>  				block_end - block_start, &poff, &plen);
> @@ -682,9 +707,7 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
>  		goto out_no_page;
>  	}
>  
> -	if (iomap->type == IOMAP_INLINE)
> -		iomap_read_inline_data(inode, page, iomap);
> -	else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
> +	if (iomap->flags & IOMAP_F_BUFFER_HEAD)
>  		status = __block_write_begin_int(page, pos, len, NULL, iomap);
>  	else
>  		status = __iomap_write_begin(inode, pos, len, page, iomap);
> @@ -761,11 +784,11 @@ iomap_write_end_inline(struct inode *inode, struct page *page,
>  {
>  	void *addr;
>  
> -	WARN_ON_ONCE(!PageUptodate(page));
> -	BUG_ON(pos + copied > PAGE_SIZE - offset_in_page(iomap->inline_data));
> +	BUG_ON(!inline_data_within_block(inode, iomap, pos + copied));
>  
>  	addr = kmap_atomic(page);
> -	memcpy(iomap->inline_data + pos, addr + pos, copied);
> +	memcpy(iomap->inline_data + offset_in_block(pos, inode),
> +	       addr + offset_in_page(pos), copied);
>  	kunmap_atomic(addr);
>  
>  	mark_inode_dirty(inode);
> @@ -1064,7 +1087,7 @@ iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
>  		const struct iomap_ops *ops)
>  {
>  	unsigned int blocksize = i_blocksize(inode);
> -	unsigned int off = pos & (blocksize - 1);
> +	unsigned int off = offset_in_block(pos, inode);
>  
>  	/* Block boundary? Nothing to do */
>  	if (!off)
> @@ -1772,21 +1795,26 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
>  	struct iov_iter *iter = dio->submit.iter;
>  	size_t copied;
>  
> -	BUG_ON(pos + length > PAGE_SIZE - offset_in_page(iomap->inline_data));
> +	BUG_ON(!inline_data_within_block(inode, iomap, pos + length));
>  
>  	if (dio->flags & IOMAP_DIO_WRITE) {
>  		loff_t size = inode->i_size;
>  
>  		if (pos > size)
> -			memset(iomap->inline_data + size, 0, pos - size);
> -		copied = copy_from_iter(iomap->inline_data + pos, length, iter);
> +			memset(iomap->inline_data +
> +			       offset_in_block(size, inode), 0, pos - size);
> +		copied = copy_from_iter(iomap->inline_data +
> +					offset_in_block(pos, inode),
> +					length, iter);
>  		if (copied) {
>  			if (pos + copied > size)
>  				i_size_write(inode, pos + copied);
>  			mark_inode_dirty(inode);
>  		}
>  	} else {
> -		copied = copy_to_iter(iomap->inline_data + pos, length, iter);
> +		copied = copy_to_iter(iomap->inline_data +
> +				      offset_in_block(pos, inode),
> +				      length, iter);
>  	}
>  	dio->size += copied;
>  	return copied;
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 2103b94cb1bf..a8a60dd2fdc0 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -131,6 +131,9 @@ static inline struct iomap_page *to_iomap_page(struct page *page)
>  	return NULL;
>  }
>  
> +void __iomap_read_inline_data(struct inode *inode, struct page *page,
> +		struct iomap *iomap);
> +
>  ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
>  		const struct iomap_ops *ops);
>  int iomap_readpage(struct page *page, const struct iomap_ops *ops);
>