Reorder structure ext4_inode_info to remove 16 bytes of alignment
padding on 64 bit builds. This shrinks its size from 904 to 888 bytes
with (CONFIG_EXT4_S_XATTR=y && CONFIG_QUOTA=n).
This will allow this structure to use one fewer cache lines.
Also change type of i_delalloc_reserved_flag to bool to better reflect
its usage.
compiled & tested on x86_64
Signed-off-by: Richard Kennedy <[email protected]>
---
patch against 2.6.36-rc1
Early testing shows more consistent results ( i.e. smaller standard
deviations) on my AMD X2 setup, but I shall re-run these tests to check
if this is repeatable.
regards
Richard
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 889ec9d..b63a8e3 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -750,10 +750,11 @@ struct ext4_inode_info {
* near to their parent directory's inode.
*/
ext4_group_t i_block_group;
- unsigned long i_state_flags; /* Dynamic state flags */
- unsigned long i_flags;
ext4_lblk_t i_dir_start_lookup;
+
+ unsigned long i_state_flags; /* Dynamic state flags */
+ unsigned long i_flags;
#ifdef CONFIG_EXT4_FS_XATTR
/*
* Extended attributes can be read independently of the main file
@@ -816,13 +817,14 @@ struct ext4_inode_info {
unsigned int i_reserved_data_blocks;
unsigned int i_reserved_meta_blocks;
unsigned int i_allocated_meta_blocks;
- unsigned short i_delalloc_reserved_flag;
- sector_t i_da_metadata_calc_last_lblock;
- int i_da_metadata_calc_len;
+ bool i_delalloc_reserved_flag;
/* on-disk additional length */
__u16 i_extra_isize;
+ sector_t i_da_metadata_calc_last_lblock;
+ int i_da_metadata_calc_len;
+
spinlock_t i_block_reservation_lock;
#ifdef CONFIG_QUOTA
/* quota space reservation, managed internally by quota code */
Richard Kennedy wrote:
> Reorder structure ext4_inode_info to remove 16 bytes of alignment
> padding on 64 bit builds. This shrinks its size from 904 to 888 bytes
> with (CONFIG_EXT4_S_XATTR=y && CONFIG_QUOTA=n).
>
> This will allow this structure to use one fewer cache lines.
>
> Also change type of i_delalloc_reserved_flag to bool to better reflect
> its usage.
>
> compiled & tested on x86_64
Looks good to me; there is still a bit of padding at the end:
qsize_t i_reserved_quota; /* 864 8 */
struct list_head i_completed_io_list; /* 872 16 */
spinlock_t i_completed_io_lock; /* 888 4 */
/* XXX 4 bytes hole, try to pack */
/* --- cacheline 14 boundary (896 bytes) --- */
ext4_io_end_t * cur_aio_dio; /* 896 8 */
tid_t i_sync_tid; /* 904 4 */
tid_t i_datasync_tid; /* 908 4 */
but it wouldn't save a cacheline anyway...
-Eric
> Signed-off-by: Richard Kennedy <[email protected]>
> ---
> patch against 2.6.36-rc1
>
> Early testing shows more consistent results ( i.e. smaller standard
> deviations) on my AMD X2 setup, but I shall re-run these tests to check
> if this is repeatable.
>
> regards
> Richard
>
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 889ec9d..b63a8e3 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -750,10 +750,11 @@ struct ext4_inode_info {
> * near to their parent directory's inode.
> */
> ext4_group_t i_block_group;
> - unsigned long i_state_flags; /* Dynamic state flags */
> - unsigned long i_flags;
>
> ext4_lblk_t i_dir_start_lookup;
> +
> + unsigned long i_state_flags; /* Dynamic state flags */
> + unsigned long i_flags;
> #ifdef CONFIG_EXT4_FS_XATTR
> /*
> * Extended attributes can be read independently of the main file
> @@ -816,13 +817,14 @@ struct ext4_inode_info {
> unsigned int i_reserved_data_blocks;
> unsigned int i_reserved_meta_blocks;
> unsigned int i_allocated_meta_blocks;
> - unsigned short i_delalloc_reserved_flag;
> - sector_t i_da_metadata_calc_last_lblock;
> - int i_da_metadata_calc_len;
> + bool i_delalloc_reserved_flag;
>
> /* on-disk additional length */
> __u16 i_extra_isize;
>
> + sector_t i_da_metadata_calc_last_lblock;
> + int i_da_metadata_calc_len;
> +
> spinlock_t i_block_reservation_lock;
> #ifdef CONFIG_QUOTA
> /* quota space reservation, managed internally by quota code */
>
>
> --
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On Fri, 2010-08-20 at 15:11 -0500, Eric Sandeen wrote:
> Richard Kennedy wrote:
> > Reorder structure ext4_inode_info to remove 16 bytes of alignment
> > padding on 64 bit builds. This shrinks its size from 904 to 888 bytes
> > with (CONFIG_EXT4_S_XATTR=y && CONFIG_QUOTA=n).
> >
> > This will allow this structure to use one fewer cache lines.
> >
> > Also change type of i_delalloc_reserved_flag to bool to better reflect
> > its usage.
> >
> > compiled & tested on x86_64
>
>
> Looks good to me; there is still a bit of padding at the end:
>
> qsize_t i_reserved_quota; /* 864 8 */
> struct list_head i_completed_io_list; /* 872 16 */
> spinlock_t i_completed_io_lock; /* 888 4 */
>
> /* XXX 4 bytes hole, try to pack */
>
> /* --- cacheline 14 boundary (896 bytes) --- */
> ext4_io_end_t * cur_aio_dio; /* 896 8 */
> tid_t i_sync_tid; /* 904 4 */
> tid_t i_datasync_tid; /* 908 4 */
>
>
> but it wouldn't save a cacheline anyway...
>
> -Eric
>
Thanks Eric, yes there is padding but we don't have anything to fill the
hole with :(
If it becomes important to save space, i_state_flags seem to be unused
in ext4 so we could possibly drop that.
With my patch applied, under slub I'm getting one more object per slab
in the ext4_inode_cache
[2.6.35] 17 objects of 960 bytes -- 4 pages per slab
[+patch] 18 objects of 896 bytes -- 4 pages per slab
So I guess that is where most of the write test performance improvement
came from.
regards
Richard
Richard Kennedy wrote:
> On Fri, 2010-08-20 at 15:11 -0500, Eric Sandeen wrote:
>> Richard Kennedy wrote:
>>> Reorder structure ext4_inode_info to remove 16 bytes of alignment
>>> padding on 64 bit builds. This shrinks its size from 904 to 888 bytes
>>> with (CONFIG_EXT4_S_XATTR=y && CONFIG_QUOTA=n).
>>>
>>> This will allow this structure to use one fewer cache lines.
>>>
>>> Also change type of i_delalloc_reserved_flag to bool to better reflect
>>> its usage.
>>>
>>> compiled & tested on x86_64
>>
>> Looks good to me; there is still a bit of padding at the end:
>>
>> qsize_t i_reserved_quota; /* 864 8 */
>> struct list_head i_completed_io_list; /* 872 16 */
>> spinlock_t i_completed_io_lock; /* 888 4 */
>>
>> /* XXX 4 bytes hole, try to pack */
>>
>> /* --- cacheline 14 boundary (896 bytes) --- */
>> ext4_io_end_t * cur_aio_dio; /* 896 8 */
>> tid_t i_sync_tid; /* 904 4 */
>> tid_t i_datasync_tid; /* 908 4 */
>>
>>
>> but it wouldn't save a cacheline anyway...
>>
>> -Eric
>>
> Thanks Eric, yes there is padding but we don't have anything to fill the
> hole with :(
>
> If it becomes important to save space, i_state_flags seem to be unused
> in ext4 so we could possibly drop that.
Actually it is used, it's just expertly hidden in:
EXT4_INODE_BIT_FNS(state, state_flags):
#define EXT4_INODE_BIT_FNS(name, field) \
static inline int ext4_test_inode_##name(struct inode *inode, int bit) \
{ \
return test_bit(bit, &EXT4_I(inode)->i_##field); \
} \
etc..
-Eric