| Message ID | 20240603131524.324224-1-sunjunchao2870@gmail.com |
|---|---|
| State | Awaiting Upstream |
| Headers | show |
| Series | ext4: Adjust the layout of the ext4_inode_info structure to save memory. | expand |
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? > > Signed-off-by: Junchao Sun <sunjunchao2870@gmail.com> Otherwise looks good. Feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> 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@suse.cz> 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@gmail.com> > > Otherwise looks good. Feel free to add: > > Reviewed-by: Jan Kara <jack@suse.cz> > > 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@suse.com> > SUSE Labs, CR
On Mon 03-06-24 22:43:16, JunChao Sun wrote: > Jan Kara <jack@suse.cz> 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. Aha, OK. Thanks for clarification! Honza
On Mon, 03 Jun 2024 21:15:24 +0800, 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. > > > [...] Applied, thanks! [1/1] ext4: Adjust the layout of the ext4_inode_info structure to save memory. commit: a3c3eecc7c876c7f2b09d9ee1acf5b8b85996cff Best regards,
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;
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. Signed-off-by: Junchao Sun <sunjunchao2870@gmail.com> --- fs/ext4/ext4.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)