Re: [PATCH 87/87] fs: move i_blocks up a few places in struct inode

[Amir Goldstein]

On Thu, Sep 28, 2023 at 2:06 PM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> The recent change to use discrete integers instead of struct timespec64
> in struct inode shaved 8 bytes off of it, but it also moves the i_lock
> into the previous cacheline, away from the fields that it protects.
>
> Move i_blocks up above the i_lock, which moves the new 4 byte hole to
> just after the timestamps, without changing the size of the structure.
>

Instead of creating an implicit hole, can you please move i_generation
to fill the 4 bytes hole.

It makes sense in the same cache line with i_ino and I could
use the vacant 4 bytes hole above i_fsnotify_mask to expand the
mask to 64bit (the 32bit event mask space is running out).

Thanks,
Amir.

> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
>  include/linux/fs.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index de902ff2938b..3e0fe0f52e7c 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -677,11 +677,11 @@ struct inode {
>         u32                     i_atime_nsec;
>         u32                     i_mtime_nsec;
>         u32                     i_ctime_nsec;
> +       blkcnt_t                i_blocks;
>         spinlock_t              i_lock; /* i_blocks, i_bytes, maybe i_size */
>         unsigned short          i_bytes;
>         u8                      i_blkbits;
>         u8                      i_write_hint;
> -       blkcnt_t                i_blocks;
>
>  #ifdef __NEED_I_SIZE_ORDERED
>         seqcount_t              i_size_seqcount;
> --
> 2.41.0
>