Re: [PATCH] block: move .bd_inode into 1st cacheline of block_device

[Ming Lei <ming.lei@redhat.com>]

On Tue, Nov 21, 2023 at 07:12:44PM +0800, Yu Kuai wrote:
> Hi,
> 
> 在 2023/11/21 18:11, Ming Lei 写道:
> > The .bd_inode field of block_device is used in IO fast path of
> > blkdev_write_iter() and blkdev_llseek(), so it is more efficient to keep
> > it into the 1st cacheline.
> > 
> > .bd_openers is only touched in open()/close(), and .bd_size_lock is only
> > for updating bdev capacity, which is in slow path too.
> > 
> > So swap .bd_inode layout with .bd_openers & .bd_size_lock to move
> > .bd_inode into the 1st cache line.
> 
> This patch looks good, do you want me do take it for a v3 for the
> other patchset?

Yeah, please take it.

> 
> And by the way, can we also move 'int bd_writers' to near 'atomic_t
> bd_fsfreeze_count' to save 8 bytes(int 64bit platform)?
> 
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 07abd0165226..a47ab9249bdd 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -63,11 +63,11 @@ struct block_device {
>         int                     bd_holders;
>         struct kobject          *bd_holder_dir;
> 
> +       int                     bd_writers;
>         atomic_t                bd_fsfreeze_count; /* number of freeze
> requests */
>         struct mutex            bd_fsfreeze_mutex; /* serialize freeze/thaw
> */
> 
>         struct partition_meta_info *bd_meta_info;
> -       int                     bd_writers;

Which tree are you talking about? I don't see 'bd_writers' in both
linus tree and block-6.7, and for-6.8/block isn't open yet.

Thanks,
Ming