Re: [PATCH] mfd: core: Reorder fields in 'struct mfd_cell' to save some memory

[Lee Jones]

On Tue, 14 Feb 2023, Christophe JAILLET wrote:

> Group some variables based on their sizes to reduce hole and avoid padding.
> On x86_64, this shrinks the size from 144 to 128 bytes.
> 
> As an example:
> 
> $ size drivers/mfd/as3722.o (Before)
>    text	   data	    bss	    dec	    hex	filename
>    9441	    680	     16	  10137	   2799	drivers/mfd/as3722.o
> 
> $ size drivers/mfd/as3722.o (After)
>    text	   data	    bss	    dec	    hex	filename
>    9345	    680	     16	  10041	   2739	drivers/mfd/as3722.o
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> ---
> Using pahole
> 
> Before:
> ======
> struct mfd_cell {
> 	const char  *              name;                 /*     0     8 */
> 	int                        id;                   /*     8     4 */
> 	int                        level;                /*    12     4 */
> 	int                        (*enable)(struct platform_device *); /*    16     8 */
> 	int                        (*disable)(struct platform_device *); /*    24     8 */
> 	int                        (*suspend)(struct platform_device *); /*    32     8 */
> 	int                        (*resume)(struct platform_device *); /*    40     8 */
> 	void *                     platform_data;        /*    48     8 */
> 	size_t                     pdata_size;           /*    56     8 */
> 	/* --- cacheline 1 boundary (64 bytes) --- */
> 	const struct software_node  * swnode;            /*    64     8 */
> 	const char  *              of_compatible;        /*    72     8 */
> 	const u64                  of_reg;               /*    80     8 */
> 	bool                       use_of_reg;           /*    88     1 */
> 
> 	/* XXX 7 bytes hole, try to pack */
> 
> 	const struct mfd_cell_acpi_match  * acpi_match;  /*    96     8 */
> 	int                        num_resources;        /*   104     4 */
> 
> 	/* XXX 4 bytes hole, try to pack */
> 
> 	const struct resource  *   resources;            /*   112     8 */
> 	bool                       ignore_resource_conflicts; /*   120     1 */
> 	bool                       pm_runtime_no_callbacks; /*   121     1 */
> 
> 	/* XXX 6 bytes hole, try to pack */
> 
> 	/* --- cacheline 2 boundary (128 bytes) --- */
> 	const char  * const *      parent_supplies;      /*   128     8 */
> 	int                        num_parent_supplies;  /*   136     4 */
> 
> 	/* size: 144, cachelines: 3, members: 20 */
> 	/* sum members: 123, holes: 3, sum holes: 17 */
> 	/* padding: 4 */
> 	/* last cacheline: 16 bytes */
> };
> 
> 
> After:
> =====
> struct mfd_cell {
> 	const char  *              name;                 /*     0     8 */
> 	int                        id;                   /*     8     4 */
> 	int                        level;                /*    12     4 */
> 	int                        (*enable)(struct platform_device *); /*    16     8 */
> 	int                        (*disable)(struct platform_device *); /*    24     8 */
> 	int                        (*suspend)(struct platform_device *); /*    32     8 */
> 	int                        (*resume)(struct platform_device *); /*    40     8 */
> 	void *                     platform_data;        /*    48     8 */
> 	size_t                     pdata_size;           /*    56     8 */
> 	/* --- cacheline 1 boundary (64 bytes) --- */
> 	const struct mfd_cell_acpi_match  * acpi_match;  /*    64     8 */
> 	const struct software_node  * swnode;            /*    72     8 */
> 	const char  *              of_compatible;        /*    80     8 */
> 	const u64                  of_reg;               /*    88     8 */
> 	bool                       use_of_reg;           /*    96     1 */
> 
> 	/* XXX 3 bytes hole, try to pack */
> 
> 	int                        num_resources;        /*   100     4 */
> 	const struct resource  *   resources;            /*   104     8 */
> 	bool                       ignore_resource_conflicts; /*   112     1 */
> 	bool                       pm_runtime_no_callbacks; /*   113     1 */
> 
> 	/* XXX 2 bytes hole, try to pack */
> 
> 	int                        num_parent_supplies;  /*   116     4 */
> 	const char  * const *      parent_supplies;      /*   120     8 */
> 
> 	/* size: 128, cachelines: 2, members: 20 */
> 	/* sum members: 123, holes: 2, sum holes: 5 */
> };
> ---
>  include/linux/mfd/core.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)

Applied, thanks

-- 
Lee Jones [李琼斯]