x86, fpu: lazy allocation of FPU area - v5

Only allocate the FPU area when the application actually uses FPU, i.e., in the
first lazy FPU trap. This could save memory for non-fpu using apps.

for example: on my system after boot, there are around 300 processes, with
only 17 using FPU.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index b795e831afd6..891af1a1b48a 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -533,6 +533,10 @@ start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
         regs->ss                = __USER_DS;
         regs->flags             = 0x200;
         set_fs(USER_DS);
+        /*
+         * Free the old FP and other extended state
+         */
+        free_thread_xstate(current);
 }
 EXPORT_SYMBOL_GPL(start_thread);