reduce size of task_struct on 64-bit machines

This past week I was playing around with that pahole tool
(http://oops.ghostprotocols.net:81/acme/dwarves/) and looking at the size
of various struct in the kernel.  I was surprised by the size of the
task_struct on x86_64, approaching 4K.  I looked through the fields in
task_struct and found that a number of them were declared as "unsigned
long" rather than "unsigned int" despite them appearing okay as 32-bit
sized fields.  On x86_64 "unsigned long" ends up being 8 bytes in size and
forces 8 byte alignment.  Is there a reason there a reason they are
"unsigned long"?

The patch below drops the size of the struct from 3808 bytes (60 64-byte
cachelines) to 3760 bytes (59 64-byte cachelines).  A couple other fields
in the task struct take a signficant amount of space:

struct thread_struct       thread;               688
struct held_lock           held_locks[30];       1680

CONFIG_LOCKDEP is turned on in the .config

[akpm@linux-foundation.org: fix printk warnings]
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 07c9cdb..74f30e0 100644 (file)
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -410,9 +410,9 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
        /* convert nsec -> ticks */
        start_time = nsec_to_clock_t(start_time);
 
-       res = sprintf(buffer,"%d (%s) %c %d %d %d %d %d %lu %lu \
+       res = sprintf(buffer,"%d (%s) %c %d %d %d %d %d %u %lu \
 %lu %lu %lu %lu %lu %ld %ld %ld %ld %d 0 %llu %lu %ld %lu %lu %lu %lu %lu \
-%lu %lu %lu %lu %lu %lu %lu %lu %d %d %lu %lu %llu\n",
+%lu %lu %lu %lu %lu %lu %lu %lu %d %d %u %u %llu\n",
                task->pid,
                tcomm,
                state,

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a170758..d9acbbb 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -801,8 +801,8 @@ struct task_struct {
        volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
        struct thread_info *thread_info;
        atomic_t usage;
-       unsigned long flags;    /* per process flags, defined below */
-       unsigned long ptrace;
+       unsigned int flags;     /* per process flags, defined below */
+       unsigned int ptrace;
 
        int lock_depth;         /* BKL lock depth */
 
@@ -825,7 +825,7 @@ struct task_struct {
        unsigned long long sched_time; /* sched_clock time spent running */
        enum sleep_type sleep_type;
 
-       unsigned long policy;
+       unsigned int policy;
        cpumask_t cpus_allowed;
        unsigned int time_slice, first_time_slice;
 
@@ -845,11 +845,11 @@ struct task_struct {
 
 /* task state */
        struct linux_binfmt *binfmt;
-       long exit_state;
+       int exit_state;
        int exit_code, exit_signal;
        int pdeath_signal;  /*  The signal sent when the parent dies  */
        /* ??? */
-       unsigned long personality;
+       unsigned int personality;
        unsigned did_exec:1;
        pid_t pid;
        pid_t tgid;
@@ -881,7 +881,7 @@ struct task_struct {
        int __user *set_child_tid;              /* CLONE_CHILD_SETTID */
        int __user *clear_child_tid;            /* CLONE_CHILD_CLEARTID */
 
-       unsigned long rt_priority;
+       unsigned int rt_priority;
        cputime_t utime, stime;
        unsigned long nvcsw, nivcsw; /* context switch counts */
        struct timespec start_time;