[RFC 2/4] add mm event counter

KAMEZAWA Hiroyuki
2009-12-18T00:46:47Z

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Add version counter to mm_struct. It's updated when
write_lock is held and released. And this patch also adds
task->mm_version. By this, mm_semaphore can provides some
operation like seqlock.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
include/linux/mm_types.h | 1 +
include/linux/sched.h | 2 +-
mm/mm_accessor.c | 29 ++++++++++++++++++++++++++---
3 files changed, 28 insertions(+), 4 deletions(-)

Index: mmotm-mm-accessor/include/linux/mm_types.h
===================================================================
--- mmotm-mm-accessor.orig/include/linux/mm_types.h
+++ mmotm-mm-accessor/include/linux/mm_types.h
@@ -216,6 +216,7 @@ struct mm_struct {
atomic_t mm_count; /* How many references to "struct mm_struct" (users count as 1) */
int map_count; /* number of VMAs */
struct rw_semaphore mmap_sem;
+ int version;
spinlock_t page_table_lock; /* Protects page tables and some counters */

struct list_head mmlist; /* List of maybe swapped mm's. These are globally strung
Index: mmotm-mm-accessor/include/linux/sched.h
===================================================================
--- mmotm-mm-accessor.orig/include/linux/sched.h
+++ mmotm-mm-accessor/include/linux/sched.h
@@ -1276,7 +1276,7 @@ struct task_struct {
struct plist_node pushable_tasks;

struct mm_struct *mm, *active_mm;
-
+ int mm_version;
/* task state */
int exit_state;
int exit_code, exit_signal;
Index: mmotm-mm-accessor/mm/mm_accessor.c
===================================================================
--- mmotm-mm-accessor.orig/mm/mm_accessor.c
+++ mmotm-mm-accessor/mm/mm_accessor.c
@@ -1,15 +1,20 @@
-#include <linux/mm_types.h>
+#include <linux/sched.h>
#include <linux/module.h>

void mm_read_lock(struct mm_struct *mm)
{
down_read(&mm->mmap_sem);
+ if (current->mm == mm && current->mm_version != mm->version)
+ current->mm_version = mm->version;
}
EXPORT_SYMBOL(mm_read_lock);

int mm_read_trylock(struct mm_struct *mm)
{
- return down_read_trylock(&mm->mmap_sem);
+ int ret = down_read_trylock(&mm->mmap_sem);
+ if (ret && current->mm == mm && current->mm_version != mm->version)
+ current->mm_version = mm->version;
+ return ret;
}
EXPORT_SYMBOL(mm_read_trylock);

@@ -22,18 +27,24 @@ EXPORT_SYMBOL(mm_read_unlock);
void mm_write_lock(struct mm_struct *mm)
{
down_write(&mm->mmap_sem);
+ mm->version++;
}
EXPORT_SYMBOL(mm_write_lock);

void mm_write_unlock(struct mm_struct *mm)
{
+ mm->version++;
up_write(&mm->mmap_sem);
}
EXPORT_SYMBOL(mm_write_unlock);

int mm_write_trylock(struct mm_struct *mm)
{
- return down_write_trylock(&mm->mmap_sem);
+ int ret = down_write_trylock(&mm->mmap_sem);
+
+ if (ret)
+ mm->version++;
+ return ret;
}
EXPORT_SYMBOL(mm_write_trylock);

@@ -45,6 +56,7 @@ EXPORT_SYMBOL(mm_is_locked);

void mm_write_to_read_lock(struct mm_struct *mm)
{
+ mm->version++;
downgrade_write(&mm->mmap_sem);
}
EXPORT_SYMBOL(mm_write_to_read_lock);
@@ -78,3 +90,14 @@ void mm_read_might_lock(struct mm_struct
might_lock_read(&mm->mmap_sem);
}
EXPORT_SYMBOL(mm_read_might_lock);
+
+/*
+ * Called when mm is accessed without read-lock or for chekcing
+ * per-thread cached value is stale or not.
+ */
+int mm_version_check(struct mm_struct *mm)
+{
+ if ((current->mm == mm) && (current->mm_version != mm->version))
+ return 0;
+ return 1;
+}