[PATCH] scheduler: reorder task_struct to reduce padding on 64bit builds

[PATCH] scheduler: reorder task_struct to reduce padding on 64bit builds

[Richard Kennedy]

reorder task_struct to reduce padding on 64bit builds
    
    removes 24 bytes on my config and /proc/slabinfo reports +1 objects per slab
    
    Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>

---
This patch removes 24 bytes of padding and allows 1 extra object per
slab on my fedora based config. 
Patch against 2.6.26-rc2 & running successfully on my AMD 64 desktop
machine.

Richard



diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5395a61..386e154 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1040,6 +1040,7 @@ struct task_struct {
 #endif
 
 	int prio, static_prio, normal_prio;
+	unsigned int rt_priority;
 	const struct sched_class *sched_class;
 	struct sched_entity se;
 	struct sched_rt_entity rt;
@@ -1123,7 +1124,6 @@ struct task_struct {
 	int __user *set_child_tid;		/* CLONE_CHILD_SETTID */
 	int __user *clear_child_tid;		/* CLONE_CHILD_CLEARTID */
 
-	unsigned int rt_priority;
 	cputime_t utime, stime, utimescaled, stimescaled;
 	cputime_t gtime;
 	cputime_t prev_utime, prev_stime;
@@ -1142,12 +1142,12 @@ struct task_struct {
 	gid_t gid,egid,sgid,fsgid;
 	struct group_info *group_info;
 	kernel_cap_t   cap_effective, cap_inheritable, cap_permitted, cap_bset;
-	unsigned securebits;
 	struct user_struct *user;
+	unsigned securebits;
 #ifdef CONFIG_KEYS
+	unsigned char jit_keyring;	/* default keyring to attach requested keys to */
 	struct key *request_key_auth;	/* assumed request_key authority */
 	struct key *thread_keyring;	/* keyring private to this thread */
-	unsigned char jit_keyring;	/* default keyring to attach requested keys to */
 #endif
 	char comm[TASK_COMM_LEN]; /* executable name excluding path
 				     - access with [gs]et_task_comm (which lock
@@ -1234,8 +1234,8 @@ struct task_struct {
 # define MAX_LOCK_DEPTH 48UL
 	u64 curr_chain_key;
 	int lockdep_depth;
-	struct held_lock held_locks[MAX_LOCK_DEPTH];
 	unsigned int lockdep_recursion;
+	struct held_lock held_locks[MAX_LOCK_DEPTH];
 #endif
 
 /* journalling filesystem info */
@@ -1263,10 +1263,6 @@ struct task_struct {
 	u64 acct_vm_mem1;	/* accumulated virtual memory usage */
 	cputime_t acct_stimexpd;/* stime since last update */
 #endif
-#ifdef CONFIG_NUMA
-  	struct mempolicy *mempolicy;
-	short il_next;
-#endif
 #ifdef CONFIG_CPUSETS
 	nodemask_t mems_allowed;
 	int cpuset_mems_generation;
@@ -1286,6 +1282,10 @@ struct task_struct {
 	struct list_head pi_state_list;
 	struct futex_pi_state *pi_state_cache;
 #endif
+#ifdef CONFIG_NUMA
+	struct mempolicy *mempolicy;
+	short il_next;
+#endif
 	atomic_t fs_excl;	/* holding fs exclusive resources */
 	struct rcu_head rcu;
 

Re: [PATCH] scheduler: reorder task_struct to reduce padding on 64bit builds

[Ingo Molnar]

* Richard Kennedy <richard@rsk.demon.co.uk> wrote:

> This patch removes 24 bytes of padding and allows 1 extra object per 
> slab on my fedora based config. Patch against 2.6.26-rc2 & running 
> successfully on my AMD 64 desktop machine.

applied, thanks. Nice patch - task_struct hasnt been field-ordering 
optimized for quite some time.

	Ingo