From: William Cohen <[EMAIL PROTECTED]> 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 [EMAIL PROTECTED]: fix printk warnings] Cc: <[email protected]> Signed-off-by: Andrew Morton <[EMAIL PROTECTED]> --- fs/proc/array.c | 4 ++-- include/linux/sched.h | 12 ++++++------ 2 files changed, 8 insertions(+), 8 deletions(-) diff -puN fs/proc/array.c~reduce-size-of-task_struct-on-64-bit-machines fs/proc/array.c --- a/fs/proc/array.c~reduce-size-of-task_struct-on-64-bit-machines +++ a/fs/proc/array.c @@ -410,9 +410,9 @@ static int do_task_stat(struct task_stru /* 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 -puN include/linux/sched.h~reduce-size-of-task_struct-on-64-bit-machines include/linux/sched.h --- a/include/linux/sched.h~reduce-size-of-task_struct-on-64-bit-machines +++ a/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; _ - To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
