From: Richard Kennedy When struct pid is built on a 64 bit platform gcc has to insert padding to maintain the correct alignment, by simply reordering its members the memory usage shrinks from 88 bytes to 80. I've successfully run with this patch on my desktop AMD64 machine. There are no significant kernel size changes to a default config.X86_64 on the latest git v2.6.26-rc1 text data bss dec hex filename 5404828 976760 734280 7115868 6c945c vmlinux 5404811 976760 734280 7115851 6c944b vmlinux.pid-patch Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton --- include/linux/pid.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN include/linux/pid.h~shrink-struct-pid-by-removing-padding-on-64-bit-builds include/linux/pid.h --- a/include/linux/pid.h~shrink-struct-pid-by-removing-padding-on-64-bit-builds +++ a/include/linux/pid.h @@ -57,10 +57,10 @@ struct upid { struct pid { atomic_t count; + unsigned int level; /* lists of tasks that use this pid */ struct hlist_head tasks[PIDTYPE_MAX]; struct rcu_head rcu; - unsigned int level; struct upid numbers[1]; }; _