Re: [PATCH v2 7/9] iomap: Convert write_count to write_bytes_pending

[Darrick J. Wong]

On Fri, Sep 11, 2020 at 12:47:05AM +0100, Matthew Wilcox (Oracle) wrote:
> Instead of counting bio segments, count the number of bytes submitted.
> This insulates us from the block layer's definition of what a 'same page'
> is, which is not necessarily clear once THPs are involved.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>

--D

> ---
>  fs/iomap/buffered-io.c | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 1cf976a8e55c..64a5cb383f30 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -27,7 +27,7 @@
>   */
>  struct iomap_page {
>  	atomic_t		read_bytes_pending;
> -	atomic_t		write_count;
> +	atomic_t		write_bytes_pending;
>  	spinlock_t		uptodate_lock;
>  	unsigned long		uptodate[];
>  };
> @@ -73,7 +73,7 @@ iomap_page_release(struct page *page)
>  	if (!iop)
>  		return;
>  	WARN_ON_ONCE(atomic_read(&iop->read_bytes_pending));
> -	WARN_ON_ONCE(atomic_read(&iop->write_count));
> +	WARN_ON_ONCE(atomic_read(&iop->write_bytes_pending));
>  	WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) !=
>  			PageUptodate(page));
>  	kfree(iop);
> @@ -1047,7 +1047,7 @@ EXPORT_SYMBOL_GPL(iomap_page_mkwrite);
>  
>  static void
>  iomap_finish_page_writeback(struct inode *inode, struct page *page,
> -		int error)
> +		int error, unsigned int len)
>  {
>  	struct iomap_page *iop = to_iomap_page(page);
>  
> @@ -1057,9 +1057,9 @@ iomap_finish_page_writeback(struct inode *inode, struct page *page,
>  	}
>  
>  	WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
> -	WARN_ON_ONCE(iop && atomic_read(&iop->write_count) <= 0);
> +	WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) <= 0);
>  
> -	if (!iop || atomic_dec_and_test(&iop->write_count))
> +	if (!iop || atomic_sub_and_test(len, &iop->write_bytes_pending))
>  		end_page_writeback(page);
>  }
>  
> @@ -1093,7 +1093,8 @@ iomap_finish_ioend(struct iomap_ioend *ioend, int error)
>  
>  		/* walk each page on bio, ending page IO on them */
>  		bio_for_each_segment_all(bv, bio, iter_all)
> -			iomap_finish_page_writeback(inode, bv->bv_page, error);
> +			iomap_finish_page_writeback(inode, bv->bv_page, error,
> +					bv->bv_len);
>  		bio_put(bio);
>  	}
>  	/* The ioend has been freed by bio_put() */
> @@ -1309,8 +1310,8 @@ iomap_add_to_ioend(struct inode *inode, loff_t offset, struct page *page,
>  
>  	merged = __bio_try_merge_page(wpc->ioend->io_bio, page, len, poff,
>  			&same_page);
> -	if (iop && !same_page)
> -		atomic_inc(&iop->write_count);
> +	if (iop)
> +		atomic_add(len, &iop->write_bytes_pending);
>  
>  	if (!merged) {
>  		if (bio_full(wpc->ioend->io_bio, len)) {
> @@ -1353,7 +1354,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  	LIST_HEAD(submit_list);
>  
>  	WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
> -	WARN_ON_ONCE(iop && atomic_read(&iop->write_count) != 0);
> +	WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) != 0);
>  
>  	/*
>  	 * Walk through the page to find areas to write back. If we run off the
> -- 
> 2.28.0
>