Re: [RFC 6/8] block/bdev: lift block size restrictions and use common definition

[Hannes Reinecke <hare@suse.de>]

On 11/13/24 10:47, Luis Chamberlain wrote:
> We now can support blocksizes larger than PAGE_SIZE, so lift
> the restriction up to the max supported page cache order and
> just bake this into a common helper used by the block layer.
> 
> We bound ourselves to 64k, because beyond that we need more testing.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
>   block/bdev.c           | 5 ++---
>   include/linux/blkdev.h | 6 +++++-
>   2 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/block/bdev.c b/block/bdev.c
> index 167d82b46781..3a5fd65f6c8e 100644
> --- a/block/bdev.c
> +++ b/block/bdev.c
> @@ -157,8 +157,7 @@ int set_blocksize(struct file *file, int size)
>   	struct inode *inode = file->f_mapping->host;
>   	struct block_device *bdev = I_BDEV(inode);
>   
> -	/* Size must be a power of two, and between 512 and PAGE_SIZE */
> -	if (size > PAGE_SIZE || size < 512 || !is_power_of_2(size))
> +	if (blk_validate_block_size(size))
>   		return -EINVAL;
>   
>   	/* Size cannot be smaller than the size supported by the device */
> @@ -185,7 +184,7 @@ int sb_set_blocksize(struct super_block *sb, int size)
>   	if (set_blocksize(sb->s_bdev_file, size))
>   		return 0;
>   	/* If we get here, we know size is power of two
> -	 * and it's value is between 512 and PAGE_SIZE */
> +	 * and it's value is larger than 512 */
>   	sb->s_blocksize = size;
>   	sb->s_blocksize_bits = blksize_bits(size);
>   	return sb->s_blocksize;
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 50c3b959da28..cc9fca1fceaa 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -25,6 +25,7 @@
>   #include <linux/uuid.h>
>   #include <linux/xarray.h>
>   #include <linux/file.h>
> +#include <linux/pagemap.h>
>   
>   struct module;
>   struct request_queue;
> @@ -268,10 +269,13 @@ static inline dev_t disk_devt(struct gendisk *disk)
>   	return MKDEV(disk->major, disk->first_minor);
>   }
>   
> +/* We should strive for 1 << (PAGE_SHIFT + MAX_PAGECACHE_ORDER) */
> +#define BLK_MAX_BLOCK_SIZE      (SZ_64K)
> +

Please make the comment a bit more descriptive, indicating that beyond 
64k more testing is required, hence it's not enabled for now.

We _could_ add a config option to make this conditional...

>   /* blk_validate_limits() validates bsize, so drivers don't usually need to */
>   static inline int blk_validate_block_size(unsigned long bsize)
>   {
> -	if (bsize < 512 || bsize > PAGE_SIZE || !is_power_of_2(bsize))
> +	if (bsize < 512 || bsize > BLK_MAX_BLOCK_SIZE || !is_power_of_2(bsize))
>   		return -EINVAL;
>   
>   	return 0;
Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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