proc: rearrange struct proc_dir_entry

struct proc_dir_entry became bit messy over years:

* move 16-bit ->mode_t before namelen to get rid of padding
* make ->in_use first field: it seems to be most used resulting in smaller code on x86_64 (defconfig):

add/remove: 0/0 grow/shrink: 7/13 up/down: 24/-67 (-43)
Function old new delta
proc_readdir_de 451 455 +4
proc_get_inode 282 286 +4
pde_put 65 69 +4
remove_proc_subtree 294 297 +3
remove_proc_entry 297 300 +3
proc_register 295 298 +3
proc_notify_change 94 97 +3
unuse_pde 27 26 -1
proc_reg_write 89 85 -4
proc_reg_unlocked_ioctl 85 81 -4
proc_reg_read 89 85 -4
proc_reg_llseek 87 83 -4
proc_reg_get_unmapped_area 123 119 -4
proc_entry_rundown 139 135 -4
proc_reg_poll 91 85 -6
proc_reg_mmap 79 73 -6
proc_get_link 55 49 -6
proc_reg_release 108 101 -7
proc_reg_open 298 291 -7
close_pdeo 228 218 -10

* move writeable fields together to a first cacheline (on x86_64), those include
* ->in_use: reference count, taken every open/read/write/close etc
* ->count: reference count, taken at readdir on every entry
* ->pde_openers: tracks (nearly) every open, dirtied
* ->pde_unload_lock: spinlock protecting ->pde_openers
* ->proc_iops, ->proc_fops, ->data: writeonce fields, used right together with previous group.

* other rarely written fields go into 1st/2nd and 2nd/3rd cacheline on 32-bit and 64-bit respectively.

Additionally on 32-bit, ->subdir, ->subdir_node, ->namelen, ->name go fully into 2nd cacheline, separated from writeable fields. They are all used during lookup.

} __randomize_layout;

Signed-off-by Alexey Dobriyan <[email protected]>

---

 fs/proc/internal.h |   23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

fs/proc/internal.h +13 -10

@@ -31,24 +31,27 @@ struct mempolicy;
  * subdir_node is used to build the rb tree "subdir" of the parent.
  */
 struct proc_dir_entry {
+	/*
+	 * number of callers into module in progress;
+	 * negative -> it's going away RSN
+	 */
+	atomic_t in_use;
+	atomic_t count;		/* use count */
+	struct list_head pde_openers;	/* who did ->open, but not ->release */
+	spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
+	struct completion *pde_unload_completion;
+	const struct inode_operations *proc_iops;
+	const struct file_operations *proc_fops;
+	void *data;
 	unsigned int low_ino;
-	umode_t mode;
 	nlink_t nlink;
 	kuid_t uid;
 	kgid_t gid;
 	loff_t size;
-	const struct inode_operations *proc_iops;
-	const struct file_operations *proc_fops;
 	struct proc_dir_entry *parent;
 	struct rb_root_cached subdir;
 	struct rb_node subdir_node;
-	void *data;
-	atomic_t count;		/* use count */
-	atomic_t in_use;	/* number of callers into module in progress; */
-			/* negative -> it's going away RSN */
-	struct completion *pde_unload_completion;
-	struct list_head pde_openers;	/* who did ->open, but not ->release */
-	spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
+	umode_t mode;
 	u8 namelen;
 	char name[];
 } __randomize_layout;

Quoted 41 lines · Alexey Dobriyan

struct proc_dir_entry became bit messy over years:

* move 16-bit ->mode_t before namelen to get rid of padding
* make ->in_use first field: it seems to be most used resulting in smaller code on x86_64 (defconfig):

add/remove: 0/0 grow/shrink: 7/13 up/down: 24/-67 (-43)
Function old new delta
proc_readdir_de 451 455 +4
proc_get_inode 282 286 +4
pde_put 65 69 +4
remove_proc_subtree 294 297 +3
remove_proc_entry 297 300 +3
proc_register 295 298 +3
proc_notify_change 94 97 +3
unuse_pde 27 26 -1
proc_reg_write 89 85 -4
proc_reg_unlocked_ioctl 85 81 -4
proc_reg_read 89 85 -4
proc_reg_llseek 87 83 -4
proc_reg_get_unmapped_area 123 119 -4
proc_entry_rundown 139 135 -4
proc_reg_poll 91 85 -6
proc_reg_mmap 79 73 -6
proc_get_link 55 49 -6
proc_reg_release 108 101 -7
proc_reg_open 298 291 -7
close_pdeo 228 218 -10

* move writeable fields together to a first cacheline (on x86_64), those include
* ->in_use: reference count, taken every open/read/write/close etc
* ->count: reference count, taken at readdir on every entry
* ->pde_openers: tracks (nearly) every open, dirtied
* ->pde_unload_lock: spinlock protecting ->pde_openers
* ->proc_iops, ->proc_fops, ->data: writeonce fields, used right together with previous group.

* other rarely written fields go into 1st/2nd and 2nd/3rd cacheline on 32-bit and 64-bit respectively.

Quoted 3 lines

Additionally on 32-bit, ->subdir, ->subdir_node, ->namelen, ->name go fully into 2nd cacheline, separated from writeable fields. They are all used during lookup.

Does

Quoted 1 line

} __randomize_layout;

pay attention to any of that?