[PATCH] ifdef ->rchar, ->wchar, ->syscr, ->syscw from task_struct

They are fat: 4x8 bytes in task_struct.
They are uncoditionally updated in every fork, read, write and sendfile.
They are used only if you have some "extended acct fields feature".

And please, please, please, read(2) knows about bytes, not characters,
why it is called "rchar"?

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Jay Lan <jlan@engr.sgi.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/base.c

@@ -1810,17 +1810,21 @@ static int proc_base_fill_cache(struct file *filp, void *dirent, filldir_t filld
 static int proc_pid_io_accounting(struct task_struct *task, char *buffer)
 {
 	return sprintf(buffer,
+#ifdef CONFIG_TASK_XACCT
 			"rchar: %llu\n"
 			"wchar: %llu\n"
 			"syscr: %llu\n"
 			"syscw: %llu\n"
+#endif
 			"read_bytes: %llu\n"
 			"write_bytes: %llu\n"
 			"cancelled_write_bytes: %llu\n",
+#ifdef CONFIG_TASK_XACCT
 			(unsigned long long)task->rchar,
 			(unsigned long long)task->wchar,
 			(unsigned long long)task->syscr,
 			(unsigned long long)task->syscw,
+#endif
 			(unsigned long long)task->ioac.read_bytes,
 			(unsigned long long)task->ioac.write_bytes,
 			(unsigned long long)task->ioac.cancelled_write_bytes);

fs/read_write.c

@@ -274,9 +274,9 @@ ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
 				ret = do_sync_read(file, buf, count, pos);
 			if (ret > 0) {
 				fsnotify_access(file->f_path.dentry);
-				current->rchar += ret;
+				add_rchar(current, ret);
 			}
-			current->syscr++;
+			inc_syscr(current);
 		}
 	}
 
@@ -332,9 +332,9 @@ ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_
 				ret = do_sync_write(file, buf, count, pos);
 			if (ret > 0) {
 				fsnotify_modify(file->f_path.dentry);
-				current->wchar += ret;
+				add_wchar(current, ret);
 			}
-			current->syscw++;
+			inc_syscw(current);
 		}
 	}
 
@@ -675,8 +675,8 @@ sys_readv(unsigned long fd, const struct iovec __user *vec, unsigned long vlen)
 	}
 
 	if (ret > 0)
-		current->rchar += ret;
-	current->syscr++;
+		add_rchar(current, ret);
+	inc_syscr(current);
 	return ret;
 }
 
@@ -696,8 +696,8 @@ sys_writev(unsigned long fd, const struct iovec __user *vec, unsigned long vlen)
 	}
 
 	if (ret > 0)
-		current->wchar += ret;
-	current->syscw++;
+		add_wchar(current, ret);
+	inc_syscw(current);
 	return ret;
 }
 
@@ -779,12 +779,12 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
 	retval = in_file->f_op->sendfile(in_file, ppos, count, file_send_actor, out_file);
 
 	if (retval > 0) {
-		current->rchar += retval;
-		current->wchar += retval;
+		add_rchar(current, retval);
+		add_wchar(current, retval);
 	}
-	current->syscr++;
-	current->syscw++;
 
+	inc_syscr(current);
+	inc_syscw(current);
 	if (*ppos > max)
 		retval = -EOVERFLOW;
 

include/linux/sched.h

@@ -1013,8 +1013,10 @@ struct task_struct {
  * to a stack based synchronous wait) if its doing sync IO.
  */
 	wait_queue_t *io_wait;
+#ifdef CONFIG_TASK_XACCT
 /* i/o counters(bytes read/written, #syscalls */
 	u64 rchar, wchar, syscr, syscw;
+#endif
 	struct task_io_accounting ioac;
 #if defined(CONFIG_TASK_XACCT)
 	u64 acct_rss_mem1;	/* accumulated rss usage */
@@ -1649,6 +1651,44 @@ extern int sched_create_sysfs_power_savings_entries(struct sysdev_class *cls);
 
 extern void normalize_rt_tasks(void);
 
+#ifdef CONFIG_TASK_XACCT
+static inline void add_rchar(struct task_struct *tsk, ssize_t amt)
+{
+	tsk->rchar += amt;
+}
+
+static inline void add_wchar(struct task_struct *tsk, ssize_t amt)
+{
+	tsk->wchar += amt;
+}
+
+static inline void inc_syscr(struct task_struct *tsk)
+{
+	tsk->syscr++;
+}
+
+static inline void inc_syscw(struct task_struct *tsk)
+{
+	tsk->syscw++;
+}
+#else
+static inline void add_rchar(struct task_struct *tsk, ssize_t amt)
+{
+}
+
+static inline void add_wchar(struct task_struct *tsk, ssize_t amt)
+{
+}
+
+static inline void inc_syscr(struct task_struct *tsk)
+{
+}
+
+static inline void inc_syscw(struct task_struct *tsk)
+{
+}
+#endif
+
 #endif /* __KERNEL__ */
 
 #endif

kernel/fork.c

@@ -1038,10 +1038,12 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	p->utime = cputime_zero;
 	p->stime = cputime_zero;
  	p->sched_time = 0;
+#ifdef CONFIG_TASK_XACCT
 	p->rchar = 0;		/* I/O counter: bytes read */
 	p->wchar = 0;		/* I/O counter: bytes written */
 	p->syscr = 0;		/* I/O counter: read syscalls */
 	p->syscw = 0;		/* I/O counter: write syscalls */
+#endif
 	task_io_accounting_init(p);
 	acct_clear_integrals(p);