Messages in this thread Patch in this message |  | | Date | Thu, 08 Feb 2007 11:14:13 -0500 | From | William Cohen <> | Subject | Size of 2.6.20 task_struct on x86_64 machines |
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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
-Will --- include/linux/sched.h.compress 2007-02-06 16:16:14.000000000 -0500 +++ include/linux/sched.h 2007-02-07 18:09:34.000000000 -0500 @@ -802,8 +802,8 @@ 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 */ @@ -826,7 +826,7 @@ 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; @@ -846,11 +846,11 @@ /* 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; @@ -882,7 +882,7 @@ 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; |  |