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>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 07c9cdbcdcac..74f30e0c0381 100644
--- 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,