Re: [PATCH 1/3] btrfs: simplify WQ_HIGHPRI handling in struct btrfs_workqueue

[David Sterba <dsterba@suse.cz>]

On Mon, Apr 18, 2022 at 04:03:43PM +0800, Qu Wenruo wrote:
> > -struct __btrfs_workqueue {
> > +struct btrfs_workqueue {
> >   	struct workqueue_struct *normal_wq;
> 
> I guess we can also rename @normal_wq here, as there is only one wq in 
> each btrfs_workqueue, no need to distinguish them in btrfs_workqueue.

Yeah now the 'normal_' prefix does not make sense.

> And since we're here, doing a pahole optimization would also be a good 
> idea (can be done in a sepearate patchset).
> 
> Especially there is a huge 16 bytes hole between @ordered_list and 
> @list_lock.

On a release build the packing is good, I don't see any holes there:

struct btrfs_work {
        btrfs_func_t               func;                 /*     0     8 */
        btrfs_func_t               ordered_func;         /*     8     8 */
        btrfs_func_t               ordered_free;         /*    16     8 */
        struct work_struct         normal_work;          /*    24    32 */
        struct list_head           ordered_list;         /*    56    16 */
        /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
        struct btrfs_workqueue *   wq;                   /*    72     8 */
        long unsigned int          flags;                /*    80     8 */

        /* size: 88, cachelines: 2, members: 7 */
        /* last cacheline: 24 bytes */
};

The fs_info structure grew a bit but it's a large one and there's still
enough space before it hits 4K.