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reduce size of task_struct on 64-bit 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

[[email protected]: fix printk warnings]
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
William Cohen 2007-05-08 00:23:41 -07:00 • committed by Linus Torvalds
commit 97dc32cdb1
2 changed files with 8 additions and 8 deletions
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4
fs/proc/array.c
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@ -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,