Re: [PATCH 07/10] btrfs: use folios for reading super blocks from the block device

[Qu Wenruo]

在 2026/9/7 07:59, Tal Zussman 写道:
> btrfs_read_disk_super() and the zoned super block log comparison go
> through read_cache_page_gfp() and page_address(), and
> btrfs_release_disk_super() recovers the page with virt_to_page(). Use
> mapping_read_folio_gfp(), folio_address(), and virt_to_folio() instead.
> This removes the last callers of read_cache_page_gfp() and put_page()
> in btrfs.
>
> Compute the super block address with offset_in_folio() as
> write_dev_supers() does, rather than assuming it is at the start of
> the page.
>
> Assisted-by: Claude:claude-fable-5-1
> Signed-off-by: Tal Zussman <tz2294@xxxxxxxxxxxx>

Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>

Thanks,
Qu

> ---
>   fs/btrfs/volumes.c | 16 +++++++---------
>   fs/btrfs/zoned.c   | 12 ++++++------
>   2 files changed, 13 insertions(+), 15 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 949e40baff33..4ddabadc9188 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -1327,16 +1327,14 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
>   
>   void btrfs_release_disk_super(struct btrfs_super_block *super)
>   {
> -	struct page *page = virt_to_page(super);
> -
> -	put_page(page);
> +	folio_put(virt_to_folio(super));
>   }
>   
>   struct btrfs_super_block *btrfs_read_disk_super(struct block_device *bdev,
>   						int copy_num, bool drop_cache)
>   {
>   	struct btrfs_super_block *super;
> -	struct page *page;
> +	struct folio *folio;
>   	u64 bytenr, bytenr_orig;
>   	struct address_space *mapping = bdev->bd_mapping;
>   	int ret;
> @@ -1357,7 +1355,7 @@ struct btrfs_super_block *btrfs_read_disk_super(struct block_device *bdev,
>   		ASSERT(copy_num == 0);
>   
>   		/*
> -		 * Drop the page of the primary superblock, so later read will
> +		 * Drop the folio of the primary superblock, so later read will
>   		 * always read from the device.
>   		 */
>   		invalidate_inode_pages2_range(mapping, bytenr >> PAGE_SHIFT,
> @@ -1365,12 +1363,12 @@ struct btrfs_super_block *btrfs_read_disk_super(struct block_device *bdev,
>   	}
>   
>   	filemap_invalidate_lock_shared(mapping);
> -	page = read_cache_page_gfp(mapping, bytenr >> PAGE_SHIFT, GFP_NOFS);
> +	folio = mapping_read_folio_gfp(mapping, bytenr >> PAGE_SHIFT, GFP_NOFS);
>   	filemap_invalidate_unlock_shared(mapping);
> -	if (IS_ERR(page))
> -		return ERR_CAST(page);
> +	if (IS_ERR(folio))
> +		return ERR_CAST(folio);
>   
> -	super = page_address(page);
> +	super = folio_address(folio) + offset_in_folio(folio, bytenr);
>   	if (btrfs_super_magic(super) != BTRFS_MAGIC ||
>   	    btrfs_super_bytenr(super) != bytenr_orig) {
>   		btrfs_release_disk_super(super);
> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> index 08a15465a087..a1ef8caaacda 100644
> --- a/fs/btrfs/zoned.c
> +++ b/fs/btrfs/zoned.c
> @@ -123,24 +123,24 @@ static int sb_write_pointer(struct block_device *bdev, struct blk_zone *zones,
>   	} else if (full[0] && full[1]) {
>   		/* Compare two super blocks */
>   		struct address_space *mapping = bdev->bd_mapping;
> -		struct page *page[BTRFS_NR_SB_LOG_ZONES];
>   		struct btrfs_super_block *super[BTRFS_NR_SB_LOG_ZONES];
>   
>   		for (int i = 0; i < BTRFS_NR_SB_LOG_ZONES; i++) {
>   			u64 zone_end = (zones[i].start + zones[i].capacity) << SECTOR_SHIFT;
>   			u64 bytenr = ALIGN_DOWN(zone_end, BTRFS_SUPER_INFO_SIZE) -
>   						BTRFS_SUPER_INFO_SIZE;
> +			struct folio *folio;
>   
>   			filemap_invalidate_lock_shared(mapping);
> -			page[i] = read_cache_page_gfp(mapping,
> -					bytenr >> PAGE_SHIFT, GFP_NOFS);
> +			folio = mapping_read_folio_gfp(mapping, bytenr >> PAGE_SHIFT,
> +						       GFP_NOFS);
>   			filemap_invalidate_unlock_shared(mapping);
> -			if (IS_ERR(page[i])) {
> +			if (IS_ERR(folio)) {
>   				if (i == 1)
>   					btrfs_release_disk_super(super[0]);
> -				return PTR_ERR(page[i]);
> +				return PTR_ERR(folio);
>   			}
> -			super[i] = page_address(page[i]);
> +			super[i] = folio_address(folio) + offset_in_folio(folio, bytenr);
>   		}
>   
>   		if (btrfs_super_generation(super[0]) >