[patch 2/2] x86, fpu: lazy allocation of FPU area - v3

Suresh Siddha
2008-03-03T23:15:26Z

[-- Attachment #1: x86-lazy-fp-allocation.patch --]
[-- Type: text/plain, Size: 5394 bytes --]

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.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
---
v3: Fixed the non-atomic calling sequence in atomic context.
v2: Ported to x86.git#testing with some name changes.
---

Index: linux-2.6-x86/arch/x86/kernel/i387.c
===================================================================
--- linux-2.6-x86.orig/arch/x86/kernel/i387.c 2008-03-03 14:15:17.000000000 -0800
+++ linux-2.6-x86/arch/x86/kernel/i387.c 2008-03-03 14:15:17.000000000 -0800
@@ -9,7 +9,6 @@
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/regset.h>
-#include <linux/bootmem.h>
#include <asm/processor.h>
#include <asm/i387.h>
#include <asm/math_emu.h>
@@ -67,7 +66,6 @@
else
xstate_size = sizeof(struct i387_fsave_struct);
#endif
- init_task.thread.xstate = alloc_bootmem(xstate_size);
}

#ifdef CONFIG_X86_64
@@ -105,6 +103,12 @@
return;
}

+ /*
+ * Memory allocation at the first usage of the FPU and other state.
+ */
+ if (!tsk->thread.xstate)
+ tsk->thread.xstate = kmem_cache_alloc(task_xstate_cachep, GFP_KERNEL);
+
if (cpu_has_fxsr) {
struct i387_fxsave_struct *fx = &tsk->thread.xstate->fxsave;

Index: linux-2.6-x86/arch/x86/kernel/process.c
===================================================================
--- linux-2.6-x86.orig/arch/x86/kernel/process.c 2008-03-03 14:15:17.000000000 -0800
+++ linux-2.6-x86/arch/x86/kernel/process.c 2008-03-03 14:15:17.000000000 -0800
@@ -5,24 +5,33 @@
#include <linux/slab.h>
#include <linux/sched.h>

-static struct kmem_cache *task_xstate_cachep;
+struct kmem_cache *task_xstate_cachep;

int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
{
*dst = *src;
- dst->thread.xstate = kmem_cache_alloc(task_xstate_cachep, GFP_KERNEL);
- if (!dst->thread.xstate)
- return -ENOMEM;
- WARN_ON((unsigned long)dst->thread.xstate & 15);
- memcpy(dst->thread.xstate, src->thread.xstate, xstate_size);
+ if (src->thread.xstate) {
+ dst->thread.xstate = kmem_cache_alloc(task_xstate_cachep, GFP_KERNEL);
+ if (!dst->thread.xstate)
+ return -ENOMEM;
+ WARN_ON((unsigned long)dst->thread.xstate & 15);
+ memcpy(dst->thread.xstate, src->thread.xstate, xstate_size);
+ }
return 0;
}

-void free_thread_info(struct thread_info *ti)
+void free_thread_xstate(struct task_struct *tsk)
{
- kmem_cache_free(task_xstate_cachep, ti->task->thread.xstate);
- ti->task->thread.xstate = NULL;
+ if (tsk->thread.xstate) {
+ kmem_cache_free(task_xstate_cachep, tsk->thread.xstate);
+ tsk->thread.xstate = NULL;
+ }
+}
+

+void free_thread_info(struct thread_info *ti)
+{
+ free_thread_xstate(ti->task);
free_pages((unsigned long)(ti), get_order(THREAD_SIZE));
}

Index: linux-2.6-x86/include/asm-x86/processor.h
===================================================================
--- linux-2.6-x86.orig/include/asm-x86/processor.h 2008-03-03 14:15:17.000000000 -0800
+++ linux-2.6-x86/include/asm-x86/processor.h 2008-03-03 14:15:17.000000000 -0800
@@ -354,6 +354,8 @@

extern void print_cpu_info(struct cpuinfo_x86 *);
extern unsigned int xstate_size;
+extern void free_thread_xstate(struct task_struct *);
+extern struct kmem_cache *task_xstate_cachep;
extern void init_scattered_cpuid_features(struct cpuinfo_x86 *c);
extern unsigned int init_intel_cacheinfo(struct cpuinfo_x86 *c);
extern unsigned short num_cache_leaves;
Index: linux-2.6-x86/arch/x86/kernel/process_32.c
===================================================================
--- linux-2.6-x86.orig/arch/x86/kernel/process_32.c 2008-03-03 14:15:17.000000000 -0800
+++ linux-2.6-x86/arch/x86/kernel/process_32.c 2008-03-03 14:15:17.000000000 -0800
@@ -524,6 +524,10 @@
regs->cs = __USER_CS;
regs->ip = new_ip;
regs->sp = new_sp;
+ /*
+ * Free the old FP and other extended state
+ */
+ free_thread_xstate(current);
}
EXPORT_SYMBOL_GPL(start_thread);

Index: linux-2.6-x86/arch/x86/kernel/process_64.c
===================================================================
--- linux-2.6-x86.orig/arch/x86/kernel/process_64.c 2008-03-03 14:15:17.000000000 -0800
+++ linux-2.6-x86/arch/x86/kernel/process_64.c 2008-03-03 14:15:17.000000000 -0800
@@ -552,6 +552,10 @@
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);

Index: linux-2.6-x86/arch/x86/kernel/traps_32.c
===================================================================
--- linux-2.6-x86.orig/arch/x86/kernel/traps_32.c 2008-03-03 14:15:17.000000000 -0800
+++ linux-2.6-x86/arch/x86/kernel/traps_32.c 2008-03-03 14:17:28.000000000 -0800
@@ -1169,9 +1169,20 @@
struct thread_info *thread = current_thread_info();
struct task_struct *tsk = thread->task;

- clts(); /* Allow maths ops (or we recurse) */
- if (!tsk_used_math(tsk))
+ if (!tsk_used_math(tsk)) {
+#ifdef CONFIG_PREEMPT
+ local_irq_enable();
+#endif
+ /*
+ * does a slab alloc which can sleep
+ */
init_fpu(tsk);
+#ifdef CONFIG_PREEMPT
+ local_irq_disable();
+#endif
+ }
+
+ clts(); /* Allow maths ops (or we recurse) */
restore_fpu(tsk);
thread->status |= TS_USEDFPU; /* So we fnsave on switch_to() */
tsk->fpu_counter++;

--