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Date: Fri, 16 Jul 2021 17:46:39 +0800
From: Gao Xiang <hsiangkao@linux.alibaba.com>
To: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 1/2] iomap: support tail packing inline read
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Hi Christoph,

On Fri, Jul 16, 2021 at 10:19:09AM +0100, Christoph Hellwig wrote:
> I'm pretty sure gfs2 supports direct writes to inline data, so we should
> not disable it.  I also think we should share the code rather than
> duplicating it.  Suggested version against the iomap-for-next branch
> attached, but this needs careful check from Andreas (please keep him on
> CC).

Thanks for your time and revising, I once thought using an
unique iomap_read_inline_data() as well but then I thought
maybe leaving iomap_read_inline_page() could make gfs2 logic
easier...

I'm fine with this modification, and will re-test on my side
as well... (hopefully Andreas could also check this and then
targeting for the next merge window since it's quite a small
change....)

Thanks,
Gao Xiang

> 
> ---
> From 6067cd3462cea80cb2739602862296db41fc5638 Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@lst.de>
> Date: Fri, 16 Jul 2021 10:52:48 +0200
> Subject: iomap: support tail packing inline read
> 
> This tries to add tail packing inline read to iomap. Different from
> the previous approach, it only marks the block range uptodate in the
> page it covers.
> 
> The write path remains untouched since EROFS cannot be used for
> testing. It'd be better to be implemented if upcoming real users care
> rather than leave untested dead code around.
> 
> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
> ---
>  fs/iomap/buffered-io.c | 56 ++++++++++++++++++++++++++++--------------
>  fs/iomap/direct-io.c   |  6 +++--
>  2 files changed, 41 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 87ccb3438becd9..2efd4bc0328995 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -207,29 +207,28 @@ struct iomap_readpage_ctx {
>  
>  static void
>  iomap_read_inline_data(struct inode *inode, struct page *page,
> -		struct iomap *iomap)
> +		struct iomap *iomap, loff_t pos, unsigned int size)
>  {
> -	size_t size = i_size_read(inode);
> +	unsigned int block_aligned_size = round_up(size, i_blocksize(inode));
> +	unsigned int poff = offset_in_page(pos);
>  	void *addr;
>  
> -	if (PageUptodate(page))
> -		return;
> -
> -	BUG_ON(page_has_private(page));
> -	BUG_ON(page->index);
> +	/* make sure that inline_data doesn't cross page boundary */
>  	BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
> +	BUG_ON(size != i_size_read(inode) - pos);
>  
>  	addr = kmap_atomic(page);
> -	memcpy(addr, iomap->inline_data, size);
> -	memset(addr + size, 0, PAGE_SIZE - size);
> +	memcpy(addr + poff, iomap->inline_data - iomap->offset + pos, size);
> +	memset(addr + poff + size, 0, block_aligned_size - size);
>  	kunmap_atomic(addr);
> -	SetPageUptodate(page);
> +
> +	iomap_set_range_uptodate(page, poff, block_aligned_size);
>  }
>  
>  static inline bool iomap_block_needs_zeroing(struct inode *inode,
>  		struct iomap *iomap, loff_t pos)
>  {
> -	return iomap->type != IOMAP_MAPPED ||
> +	return (iomap->type != IOMAP_MAPPED && iomap->type != IOMAP_INLINE) ||
>  		(iomap->flags & IOMAP_F_NEW) ||
>  		pos >= i_size_read(inode);
>  }
> @@ -240,20 +239,18 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>  {
>  	struct iomap_readpage_ctx *ctx = data;
>  	struct page *page = ctx->cur_page;
> -	struct iomap_page *iop;
> +	struct iomap_page *iop = NULL;
>  	bool same_page = false, is_contig = false;
>  	loff_t orig_pos = pos;
>  	unsigned poff, plen;
>  	sector_t sector;
>  
> -	if (iomap->type == IOMAP_INLINE) {
> -		WARN_ON_ONCE(pos);
> -		iomap_read_inline_data(inode, page, iomap);
> -		return PAGE_SIZE;
> -	}
> +	if (iomap->type == IOMAP_INLINE && !pos)
> +		WARN_ON_ONCE(to_iomap_page(page) != NULL);
> +	else
> +		iop = iomap_page_create(inode, page);
>  
>  	/* zero post-eof blocks as the page may be mapped */
> -	iop = iomap_page_create(inode, page);
>  	iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
>  	if (plen == 0)
>  		goto done;
> @@ -264,6 +261,15 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>  		goto done;
>  	}
>  
> +	if (iomap->type == IOMAP_INLINE) {
> +		iomap_read_inline_data(inode, page, iomap, pos, plen);
> +		/*
> +		 * TODO: the old code used to return PAGE_SIZE here
> +		 * unconditionally.  I think the actual i_size return should
> +		 * be fine for gfs2 as well, but please double check.
> +		 */
> +		goto done;
> +	}
>  	ctx->cur_page_in_bio = true;
>  	if (iop)
>  		atomic_add(plen, &iop->read_bytes_pending);
> @@ -589,6 +595,18 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
>  	return 0;
>  }
>  
> +static int iomap_write_begin_inline(struct inode *inode, loff_t pos,
> +		struct page *page, struct iomap *srcmap)
> +{
> +	/* needs more work for the tailpacking case, disable for now */
> +	if (WARN_ON_ONCE(pos != 0))
> +		return -EIO;
> +	if (PageUptodate(page))
> +		return 0;
> +	iomap_read_inline_data(inode, page, srcmap, pos, i_size_read(inode));
> +	return 0;
> +}
> +
>  static int
>  iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
>  		struct page **pagep, struct iomap *iomap, struct iomap *srcmap)
> @@ -618,7 +636,7 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
>  	}
>  
>  	if (srcmap->type == IOMAP_INLINE)
> -		iomap_read_inline_data(inode, page, srcmap);
> +		status = iomap_write_begin_inline(inode, pos, page, srcmap);
>  	else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
>  		status = __block_write_begin_int(page, pos, len, NULL, srcmap);
>  	else
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 9398b8c31323b3..a70a8632df226f 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -380,7 +380,8 @@ 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));
> +	/* inline data must be inside a single page */
> +	BUG_ON(length > PAGE_SIZE - offset_in_page(iomap->inline_data));
>  
>  	if (dio->flags & IOMAP_DIO_WRITE) {
>  		loff_t size = inode->i_size;
> @@ -394,7 +395,8 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
>  			mark_inode_dirty(inode);
>  		}
>  	} else {
> -		copied = copy_to_iter(iomap->inline_data + pos, length, iter);
> +		copied = copy_to_iter(iomap->inline_data + pos - iomap->offset,
> +				length, iter);
>  	}
>  	dio->size += copied;
>  	return copied;
> -- 
> 2.30.2