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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>
This commit is contained in:
William Cohen 2007-05-08 00:23:41 -07:00 committed by Linus Torvalds
parent 4d7bf11d64
commit 97dc32cdb1
2 changed files with 8 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
fs/proc/array.c
View File

@ -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,

12
include/linux/sched.h
View File

@ -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;