Re: [PATCH 05/10] btrfs: Remove btrfs_get_extent indirection from __do_readpage

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2020/9/9 下午5:49, Nikolay Borisov wrote:
> Now that this function is only responsible for reading data pages it's
> no longer necessary to pass get_extent_t parameter across several
> layers of functions. This patch removes this parameter from multiple
> functions: __get_extent_map/__do_readpage/__extent_read_full_page/
> extent_read_full_page and simply calls btrfs_get_extent directly in
> __get_extent_map.

Then it would be much nicer to see a patch renaming all these functions
to specifically name as like
get_data_extent_map/do_data_readpage/data_extent_read_full_page.

The current extent/page naming is too generic, not really distinguish
the completely different path between data and metadata.

And maybe split extent_io into meta_io and data_io. <- That may be
overkilled I guess...

Thanks,
Qu

>
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  fs/btrfs/extent_io.c | 31 ++++++++++++-------------------
>  fs/btrfs/extent_io.h |  3 +--
>  fs/btrfs/inode.c     |  2 +-
>  3 files changed, 14 insertions(+), 22 deletions(-)
>
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 1789a7931312..4c04d3655538 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -3110,8 +3110,7 @@ void set_page_extent_mapped(struct page *page)
>
>  static struct extent_map *
>  __get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
> -		 u64 start, u64 len, get_extent_t *get_extent,
> -		 struct extent_map **em_cached)
> +		 u64 start, u64 len, struct extent_map **em_cached)
>  {
>  	struct extent_map *em;
>
> @@ -3127,7 +3126,7 @@ __get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
>  		*em_cached = NULL;
>  	}
>
> -	em = get_extent(BTRFS_I(inode), page, start, len);
> +	em = btrfs_get_extent(BTRFS_I(inode), page, start, len);
>  	if (em_cached && !IS_ERR_OR_NULL(em)) {
>  		BUG_ON(*em_cached);
>  		refcount_inc(&em->refs);
> @@ -3142,9 +3141,7 @@ __get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
>   * XXX JDM: This needs looking at to ensure proper page locking
>   * return 0 on success, otherwise return error
>   */
> -static int __do_readpage(struct page *page,
> -			 get_extent_t *get_extent,
> -			 struct extent_map **em_cached,
> +static int __do_readpage(struct page *page, struct extent_map **em_cached,
>  			 struct bio **bio, int mirror_num,
>  			 unsigned long *bio_flags, unsigned int read_flags,
>  			 u64 *prev_em_start)
> @@ -3211,7 +3208,7 @@ static int __do_readpage(struct page *page,
>  		if (pg_offset != 0)
>  			trace_printk("PG offset: %lu iosize: %lu\n", pg_offset, iosize);
>  		em = __get_extent_map(inode, page, pg_offset, cur,
> -				      end - cur + 1, get_extent, em_cached);
> +				      end - cur + 1, em_cached);
>  		if (IS_ERR_OR_NULL(em)) {
>  			SetPageError(page);
>  			unlock_extent(tree, cur, end);
> @@ -3364,16 +3361,14 @@ static inline void contiguous_readpages(struct page *pages[], int nr_pages,
>  	btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);
>
>  	for (index = 0; index < nr_pages; index++) {
> -		__do_readpage(pages[index], btrfs_get_extent, em_cached,
> -				bio, 0, bio_flags, REQ_RAHEAD, prev_em_start);
> +		__do_readpage(pages[index], em_cached, bio, 0, bio_flags,
> +			      REQ_RAHEAD, prev_em_start);
>  		put_page(pages[index]);
>  	}
>  }
>
> -static int __extent_read_full_page(struct page *page,
> -				   get_extent_t *get_extent,
> -				   struct bio **bio, int mirror_num,
> -				   unsigned long *bio_flags,
> +static int __extent_read_full_page(struct page *page, struct bio **bio,
> +				   int mirror_num, unsigned long *bio_flags,
>  				   unsigned int read_flags)
>  {
>  	struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
> @@ -3383,20 +3378,18 @@ static int __extent_read_full_page(struct page *page,
>
>  	btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);
>
> -	ret = __do_readpage(page, get_extent, NULL, bio, mirror_num,
> -			    bio_flags, read_flags, NULL);
> +	ret = __do_readpage(page, NULL, bio, mirror_num, bio_flags, read_flags,
> +			    NULL);
>  	return ret;
>  }
>
> -int extent_read_full_page(struct page *page, get_extent_t *get_extent,
> -			  int mirror_num)
> +int extent_read_full_page(struct page *page, int mirror_num)
>  {
>  	struct bio *bio = NULL;
>  	unsigned long bio_flags = 0;
>  	int ret;
>
> -	ret = __extent_read_full_page(page, get_extent, &bio, mirror_num,
> -				      &bio_flags, 0);
> +	ret = __extent_read_full_page(page, &bio, mirror_num, &bio_flags, 0);
>  	if (bio)
>  		ret = submit_one_bio(bio, mirror_num, bio_flags);
>  	return ret;
> diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
> index 41621731a4fe..57786feffdbf 100644
> --- a/fs/btrfs/extent_io.h
> +++ b/fs/btrfs/extent_io.h
> @@ -193,8 +193,7 @@ typedef struct extent_map *(get_extent_t)(struct btrfs_inode *inode,
>  int try_release_extent_mapping(struct page *page, gfp_t mask);
>  int try_release_extent_buffer(struct page *page);
>
> -int extent_read_full_page(struct page *page, get_extent_t *get_extent,
> -			  int mirror_num);
> +int extent_read_full_page(struct page *page, int mirror_num);
>  int extent_write_full_page(struct page *page, struct writeback_control *wbc);
>  int extent_write_locked_range(struct inode *inode, u64 start, u64 end,
>  			      int mode);
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index a7b62b93246b..c8d1d935c8c7 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -8036,7 +8036,7 @@ static int btrfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>
>  int btrfs_readpage(struct file *file, struct page *page)
>  {
> -	return extent_read_full_page(page, btrfs_get_extent, 0);
> +	return extent_read_full_page(page, 0);
>  }
>
>  static int btrfs_writepage(struct page *page, struct writeback_control *wbc)
>