sysfs: slim down sysfs_dirent->s_active
Make sysfs_dirent->s_active an atomic_t instead of rwsem. This
reduces the size of sysfs_dirent from 136 to 104 on 64bit and from 76
to 60 on 32bit with lock debugging turned off. With lock debugging
turned on the reduction is much larger.
s_active starts at zero and each active reference increments s_active.
Putting a reference decrements s_active. Deactivation subtracts
SD_DEACTIVATED_BIAS which is currently INT_MIN and assumed to be small
enough to make s_active negative. If s_active is negative,
sysfs_get() no longer grants new references. Deactivation succeeds
immediately if there is no active user; otherwise, it waits using a
completion for the last put.
Due to the removal of lockdep tricks, this change makes things less
trickier in release_sysfs_dirent(). As all the complexity is
contained in three s_active functions, I think it's more readable this
way.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index f8779ea..ae006b0 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -21,7 +21,7 @@
*/
struct sysfs_dirent {
atomic_t s_count;
- struct rw_semaphore s_active;
+ atomic_t s_active;
struct sysfs_dirent * s_parent;
struct list_head s_sibling;
struct list_head s_children;
@@ -42,16 +42,7 @@
atomic_t s_event;
};
-/*
- * A sysfs file which deletes another file when written to need to
- * write lock the s_active of the victim while its s_active is read
- * locked for the write operation. Tell lockdep that this is okay.
- */
-enum sysfs_s_active_class
-{
- SYSFS_S_ACTIVE_NORMAL, /* file r/w access, etc - default */
- SYSFS_S_ACTIVE_DEACTIVATE, /* file deactivation */
-};
+#define SD_DEACTIVATED_BIAS INT_MIN
extern struct vfsmount * sysfs_mount;
extern struct kmem_cache *sysfs_dir_cachep;