RDMA/restrack: Reorder fields in 'struct rdma_restrack_entry'

  Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size from 136 to 128 bytes.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
Using pahole

Before:
======
struct rdma_restrack_entry {
	bool                       valid;                /*     0     1 */
	u8                         no_track:1;           /*     1: 0  1 */

	/* XXX 7 bits hole, try to pack */
	/* XXX 2 bytes hole, try to pack */

	struct kref                kref;                 /*     4     4 */
	struct completion          comp;                 /*     8    96 */
	/* --- cacheline 1 boundary (64 bytes) was 40 bytes ago --- */
	struct task_struct *       task;                 /*   104     8 */
	const char  *              kern_name;            /*   112     8 */
	enum rdma_restrack_type    type;                 /*   120     4 */
	bool                       user;                 /*   124     1 */

	/* XXX 3 bytes hole, try to pack */

	/* --- cacheline 2 boundary (128 bytes) --- */
	u32                        id;                   /*   128     4 */

	/* size: 136, cachelines: 3, members: 9 */
	/* sum members: 126, holes: 2, sum holes: 5 */
	/* sum bitfield members: 1 bits, bit holes: 1, sum bit holes: 7 bits */
	/* padding: 4 */
	/* last cacheline: 8 bytes */
};

After:
=====
struct rdma_restrack_entry {
	bool                       valid;                /*     0     1 */
	u8                         no_track:1;           /*     1: 0  1 */

	/* XXX 7 bits hole, try to pack */

	bool                       user;                 /*     2     1 */

	/* XXX 1 byte hole, try to pack */

	struct kref                kref;                 /*     4     4 */
	struct completion          comp;                 /*     8    96 */
	/* --- cacheline 1 boundary (64 bytes) was 40 bytes ago --- */
	struct task_struct *       task;                 /*   104     8 */
	const char  *              kern_name;            /*   112     8 */
	enum rdma_restrack_type    type;                 /*   120     4 */
	u32                        id;                   /*   124     4 */

	/* size: 128, cachelines: 2, members: 9 */
	/* sum members: 126, holes: 1, sum holes: 1 */
	/* sum bitfield members: 1 bits, bit holes: 1, sum bit holes: 7 bits */
};
---
 include/rdma/restrack.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
  

On Tue, Feb 14, 2023 at 01:53:52PM +0100, Christophe JAILLET wrote:
> diff --git a/include/rdma/restrack.h b/include/rdma/restrack.h
> index 8b7c46daeb07..da53fefe6f9e 100644
> --- a/include/rdma/restrack.h
> +++ b/include/rdma/restrack.h
> @@ -80,6 +80,10 @@ struct rdma_restrack_entry {
>  	 * query stage.
>  	 */
>  	u8			no_track : 1;
> +	/**
> +	 * @user: user resource
> +	 */
> +	bool			user;

Can we combine this into the bitfield above?

Jason
  

Le 14/02/2023 à 14:08, Jason Gunthorpe a écrit :
> On Tue, Feb 14, 2023 at 01:53:52PM +0100, Christophe JAILLET wrote:
>> diff --git a/include/rdma/restrack.h b/include/rdma/restrack.h
>> index 8b7c46daeb07..da53fefe6f9e 100644
>> --- a/include/rdma/restrack.h
>> +++ b/include/rdma/restrack.h
>> @@ -80,6 +80,10 @@ struct rdma_restrack_entry {
>>   	 * query stage.
>>   	 */
>>   	u8			no_track : 1;
>> +	/**
>> +	 * @user: user resource
>> +	 */
>> +	bool			user;
> 
> Can we combine this into the bitfield above?
> 
> Jason
> 
Hi,

and even above, we have
	bool	valid;

I wanted to keep the changes as minimal as possible, but I can change 
them all in a single bitfield.


Do you want code such as:
static void rdma_restrack_attach_task(struct rdma_restrack_entry *res,
				      struct task_struct *task)
{
	if (WARN_ON_ONCE(!task))
		return;

	if (res->task)
		put_task_struct(res->task);
	get_task_struct(task);
	res->task = task;
	res->user = true;			<--------
}

to be changed with 0/1 instead of false/true?

Apparently gcc 11.3 is fine with using true with u8:1, but I don't find 
it really logical.

CJ
  

On Tue, Feb 14, 2023 at 03:34:21PM +0100, Christophe JAILLET wrote:
> Le 14/02/2023 à 14:08, Jason Gunthorpe a écrit :
> > On Tue, Feb 14, 2023 at 01:53:52PM +0100, Christophe JAILLET wrote:
> > > diff --git a/include/rdma/restrack.h b/include/rdma/restrack.h
> > > index 8b7c46daeb07..da53fefe6f9e 100644
> > > --- a/include/rdma/restrack.h
> > > +++ b/include/rdma/restrack.h
> > > @@ -80,6 +80,10 @@ struct rdma_restrack_entry {
> > >   	 * query stage.
> > >   	 */
> > >   	u8			no_track : 1;
> > > +	/**
> > > +	 * @user: user resource
> > > +	 */
> > > +	bool			user;
> > 
> > Can we combine this into the bitfield above?
> > 
> > Jason
> > 
> Hi,
> 
> and even above, we have
> 	bool	valid;
> 
> I wanted to keep the changes as minimal as possible, but I can change them
> all in a single bitfield.

IIRC it needs to be checked, I vaugely remember valid can't be a
bitfield because it is an atomic
> Do you want code such as:
> static void rdma_restrack_attach_task(struct rdma_restrack_entry *res,
> 				      struct task_struct *task)
> {
> 	if (WARN_ON_ONCE(!task))
> 		return;
> 
> 	if (res->task)
> 		put_task_struct(res->task);
> 	get_task_struct(task);
> 	res->task = task;
> 	res->user = true;			<--------
> }
>
> to be changed with 0/1 instead of false/true?

I'd keep with true/false

Ideally the bitfield itself would be bool type too

> Apparently gcc 11.3 is fine with using true with u8:1, but I don't find it
> really logical.

Bool types can be casted to integers in defined ways, it is pretty
normal.

Jason
  

On Tue, Feb 14, 2023 at 11:01:00AM -0400, Jason Gunthorpe wrote:
> On Tue, Feb 14, 2023 at 03:34:21PM +0100, Christophe JAILLET wrote:
> > Le 14/02/2023 à 14:08, Jason Gunthorpe a écrit :
> > > On Tue, Feb 14, 2023 at 01:53:52PM +0100, Christophe JAILLET wrote:
> > > > diff --git a/include/rdma/restrack.h b/include/rdma/restrack.h
> > > > index 8b7c46daeb07..da53fefe6f9e 100644
> > > > --- a/include/rdma/restrack.h
> > > > +++ b/include/rdma/restrack.h
> > > > @@ -80,6 +80,10 @@ struct rdma_restrack_entry {
> > > >   	 * query stage.
> > > >   	 */
> > > >   	u8			no_track : 1;
> > > > +	/**
> > > > +	 * @user: user resource
> > > > +	 */
> > > > +	bool			user;
> > > 
> > > Can we combine this into the bitfield above?
> > > 
> > > Jason
> > > 
> > Hi,
> > 
> > and even above, we have
> > 	bool	valid;
> > 
> > I wanted to keep the changes as minimal as possible, but I can change them
> > all in a single bitfield.
> 
> IIRC it needs to be checked, I vaugely remember valid can't be a
> bitfield because it is an atomic

I don't remember anything like this.

Thanks
  

Le 15/02/2023 à 12:31, Leon Romanovsky a écrit :
> On Tue, Feb 14, 2023 at 11:01:00AM -0400, Jason Gunthorpe wrote:
>> On Tue, Feb 14, 2023 at 03:34:21PM +0100, Christophe JAILLET wrote:
>>> Le 14/02/2023 à 14:08, Jason Gunthorpe a écrit :
>>>> On Tue, Feb 14, 2023 at 01:53:52PM +0100, Christophe JAILLET wrote:
>>>>> diff --git a/include/rdma/restrack.h b/include/rdma/restrack.h
>>>>> index 8b7c46daeb07..da53fefe6f9e 100644
>>>>> --- a/include/rdma/restrack.h
>>>>> +++ b/include/rdma/restrack.h
>>>>> @@ -80,6 +80,10 @@ struct rdma_restrack_entry {
>>>>>    	 * query stage.
>>>>>    	 */
>>>>>    	u8			no_track : 1;
>>>>> +	/**
>>>>> +	 * @user: user resource
>>>>> +	 */
>>>>> +	bool			user;
>>>>
>>>> Can we combine this into the bitfield above?
>>>>
>>>> Jason
>>>>
>>> Hi,
>>>
>>> and even above, we have
>>> 	bool	valid;
>>>
>>> I wanted to keep the changes as minimal as possible, but I can change them
>>> all in a single bitfield.
>>
>> IIRC it needs to be checked, I vaugely remember valid can't be a
>> bitfield because it is an atomic
> 
> I don't remember anything like this.
> 
> Thanks
> 

If I understand code correctly, 'valid' is only used in 
rdma_restrack_add() and rdma_restrack_del().

I don't think that any atomic behavior is in place in these functions.


I'll send in the coming days a v2 which changes 'valid', 'no_track' and 
'user' as bool:1.

CJ