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SubjectRe: [PATCH v3 1/3] block: move .bd_inode into 1st cacheline of block_device
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Hi,

在 2023/11/22 18:31, Yu Kuai 写道:
> From: Ming Lei <ming.lei@redhat.com>
>
> 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.
>
> Cc: Yu Kuai <yukuai3@huawei.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
> include/linux/blk_types.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index d5c5e59ddbd2..f7d40692dd94 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -49,9 +49,10 @@ struct block_device {
> bool bd_write_holder;
> bool bd_has_submit_bio;
> dev_t bd_dev;
> + struct inode *bd_inode; /* will die */

Now that we're here, and bdev->bd_inode is always point to the
field inode of struct bdev_inode, which is next to the field bdev,
and the comment "will die" have been exist for a long time.

Maybe I can try to replace all the reference of bdev->bd_inode with
a helper, and then remove this field, then it'll be acceptable to add
a new field "unsigned long bd_flags".

Thanks,
Kuai


> +
> atomic_t bd_openers;
> spinlock_t bd_size_lock; /* for bd_inode->i_size updates */
> - struct inode * bd_inode; /* will die */
> void * bd_claiming;
> void * bd_holder;
> const struct blk_holder_ops *bd_holder_ops;
>

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