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tty: shrink the size of struct tty_struct by 40 bytes 

It's been a long time since anyone has looked at what struct tty_struct
looks like in memory, turns out there was a ton of holes.

So move things around a bit, change one variable (closing) from being an
int to a bool (it is only being tested for 0/1), and we end up saving 40
bytes per structure overall on x86-64 systems.

Before this patch:
	/* size: 696, cachelines: 11, members: 37 */
	/* sum members: 665, holes: 8, sum holes: 31 */
	/* forced alignments: 2, forced holes: 1, sum forced holes: 4 */
	/* last cacheline: 56 bytes */

After this change:
	/* size: 656, cachelines: 11, members: 37 */
	/* sum members: 654, holes: 1, sum holes: 2 */
	/* forced alignments: 2 */
	/* last cacheline: 16 bytes */

Cc: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/2023082519-cobbler-unholy-8d1f@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Greg Kroah-Hartman 2023-08-25 17:28:20 +02:00
parent a84853c595
commit ebf05c7dc9
1 changed files with 9 additions and 9 deletions
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18
include/linux/tty.h
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@ -192,13 +192,14 @@ struct tty_operations;
*/
struct tty_struct {
struct kref kref;
int index;
struct device *dev;
struct tty_driver *driver;
struct tty_port *port;
const struct tty_operations *ops;
int index;
struct ld_semaphore ldisc_sem;
struct tty_ldisc *ldisc;
struct ld_semaphore ldisc_sem;
struct mutex atomic_write_lock;
struct mutex legacy_mutex;
@ -209,6 +210,7 @@ struct tty_struct {
char name[64];
unsigned long flags;
int count;
unsigned int receive_room;
struct winsize winsize;
struct {
@ -219,16 +221,16 @@ struct tty_struct {
} __aligned(sizeof(unsigned long)) flow;
struct {
spinlock_t lock;
struct pid *pgrp;
struct pid *session;
spinlock_t lock;
unsigned char pktstatus;
bool packet;
unsigned long unused[0];
} __aligned(sizeof(unsigned long)) ctrl;
bool hw_stopped;
unsigned int receive_room;
bool closing;
int flow_change;
struct tty_struct *link;
@ -239,15 +241,13 @@ struct tty_struct {
void *disc_data;
void *driver_data;
spinlock_t files_lock;
int write_cnt;
unsigned char *write_buf;
struct list_head tty_files;
#define N_TTY_BUF_SIZE 4096
int closing;
unsigned char *write_buf;
int write_cnt;
struct work_struct SAK_work;
struct tty_port *port;
} __randomize_layout;
/* Each of a tty's open files has private_data pointing to tty_file_private */