Jan Kara <jack@xxxxxxx> 于2024年6月3日周一 22:07写道：
>
> On Mon 03-06-24 21:15:24, Junchao Sun wrote:
> > Using pahole, we can see that there are some padding holes
> > in the current ext4_inode_info structure. Adjusting the
> > layout of ext4_inode_info can reduce these holes,
> > resulting in the size of the structure decreasing
> > from 2424 bytes to 2408 bytes.
>
>
> > But AFAICT this will save two holes 4 bytes each so only 8 bytes in total?
> > Not 16?
Indeed it's 16.
Consider the layout int a; hole 0; int b; hole 1; And then move int b
to hole 0 position, this adjustment resulted in saving 8 bytes. There
are two adjustments like this, so it's 16. And GDB confirmed this.
>
> >
> > Signed-off-by: Junchao Sun <sunjunchao2870@xxxxxxxxx>
>
> Otherwise looks good. Feel free to add:
>
> Reviewed-by: Jan Kara <jack@xxxxxxx>
>
> Honza
>
> > ---
> > fs/ext4/ext4.h | 10 +++++-----
> > 1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > index 023571f8dd1b..42bcd4f749a8 100644
> > --- a/fs/ext4/ext4.h
> > +++ b/fs/ext4/ext4.h
> > @@ -1055,6 +1055,7 @@ struct ext4_inode_info {
> >
> > /* Number of ongoing updates on this inode */
> > atomic_t i_fc_updates;
> > + atomic_t i_unwritten; /* Nr. of inflight conversions pending */
> >
> > /* Fast commit wait queue for this inode */
> > wait_queue_head_t i_fc_wait;
> > @@ -1103,6 +1104,10 @@ struct ext4_inode_info {
> >
> > /* mballoc */
> > atomic_t i_prealloc_active;
> > +
> > + /* allocation reservation info for delalloc */
> > + /* In case of bigalloc, this refer to clusters rather than blocks */
> > + unsigned int i_reserved_data_blocks;
> > struct rb_root i_prealloc_node;
> > rwlock_t i_prealloc_lock;
> >
> > @@ -1119,10 +1124,6 @@ struct ext4_inode_info {
> > /* ialloc */
> > ext4_group_t i_last_alloc_group;
> >
> > - /* allocation reservation info for delalloc */
> > - /* In case of bigalloc, this refer to clusters rather than blocks */
> > - unsigned int i_reserved_data_blocks;
> > -
> > /* pending cluster reservations for bigalloc file systems */
> > struct ext4_pending_tree i_pending_tree;
> >
> > @@ -1146,7 +1147,6 @@ struct ext4_inode_info {
> > */
> > struct list_head i_rsv_conversion_list;
> > struct work_struct i_rsv_conversion_work;
> > - atomic_t i_unwritten; /* Nr. of inflight conversions pending */
> >
> > spinlock_t i_block_reservation_lock;
> >
> > --
> > 2.39.2
> >
> --
> Jan Kara <jack@xxxxxxxx>
> SUSE Labs, CR
