lockdep: shrink held_lock structure

struct held_lock {
        u64                        prev_chain_key;       /*     0     8 */
        struct lock_class *        class;                /*     8     8 */
        long unsigned int          acquire_ip;           /*    16     8 */
        struct lockdep_map *       instance;             /*    24     8 */
        int                        irq_context;          /*    32     4 */
        int                        trylock;              /*    36     4 */
        int                        read;                 /*    40     4 */
        int                        check;                /*    44     4 */
        int                        hardirqs_off;         /*    48     4 */

        /* size: 56, cachelines: 1 */
        /* padding: 4 */
        /* last cacheline: 56 bytes */
};

struct held_lock {
        u64                        prev_chain_key;       /*     0     8 */
        long unsigned int          acquire_ip;           /*     8     8 */
        struct lockdep_map *       instance;             /*    16     8 */
        unsigned int               class_idx:11;         /*    24:21  4 */
        unsigned int               irq_context:2;        /*    24:19  4 */
        unsigned int               trylock:1;            /*    24:18  4 */
        unsigned int               read:2;               /*    24:16  4 */
        unsigned int               check:2;              /*    24:14  4 */
        unsigned int               hardirqs_off:1;       /*    24:13  4 */

        /* size: 32, cachelines: 1 */
        /* padding: 4 */
        /* bit_padding: 13 bits */
        /* last cacheline: 32 bytes */
};

[mingo@elte.hu: shrunk hlock->class too]
[peterz@infradead.org: fixup bit sizes]
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

include/linux/lockdep.h

@@ -190,6 +190,9 @@ struct lock_chain {
 	u64				chain_key;
 };
 
+#define MAX_LOCKDEP_KEYS_BITS		11
+#define MAX_LOCKDEP_KEYS		(1UL << MAX_LOCKDEP_KEYS_BITS)
+
 struct held_lock {
 	/*
 	 * One-way hash of the dependency chain up to this point. We
@@ -206,14 +209,13 @@ struct held_lock {
 	 * with zero), here we store the previous hash value:
 	 */
 	u64				prev_chain_key;
-	struct lock_class		*class;
 	unsigned long			acquire_ip;
 	struct lockdep_map		*instance;
-
 #ifdef CONFIG_LOCK_STAT
 	u64 				waittime_stamp;
 	u64				holdtime_stamp;
 #endif
+	unsigned int			class_idx:MAX_LOCKDEP_KEYS_BITS;
 	/*
 	 * The lock-stack is unified in that the lock chains of interrupt
 	 * contexts nest ontop of process context chains, but we 'separate'
@@ -227,11 +229,11 @@ struct held_lock {
 	 * The following field is used to detect when we cross into an
 	 * interrupt context:
 	 */
-	int				irq_context;
-	int				trylock;
-	int				read;
-	int				check;
-	int				hardirqs_off;
+	unsigned int irq_context:2; /* bit 0 - soft, bit 1 - hard */
+	unsigned int trylock:1;
+	unsigned int read:2;        /* see lock_acquire() comment */
+	unsigned int check:2;       /* see lock_acquire() comment */
+	unsigned int hardirqs_off:1;
 };
 
 /*

kernel/lockdep_internals.h

@@ -17,9 +17,6 @@
  */
 #define MAX_LOCKDEP_ENTRIES	8192UL
 
-#define MAX_LOCKDEP_KEYS_BITS	11
-#define MAX_LOCKDEP_KEYS	(1UL << MAX_LOCKDEP_KEYS_BITS)
-
 #define MAX_LOCKDEP_CHAINS_BITS	14
 #define MAX_LOCKDEP_CHAINS	(1UL << MAX_LOCKDEP_CHAINS_BITS)