Re: [PATCH v3 08/11] slub: Replace cmpxchg_double()

Peter Zijlstra
2023-05-30T19:34:10Z

On Tue, May 30, 2023 at 04:22:32PM +0200, Peter Zijlstra wrote:

> Yet another alternative is using a struct type and an equality function,
> just for this.

The best I could come up with in the regard is the below. It builds on
HPPA64 and x86_64, but I've not ran it yet.

(also, the introduction of this_cpu_try_cmpxchg() should probably be
split out into its own patch)

--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -99,6 +99,15 @@ do { \
__ret; \
})

+#define raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval) \
+({ \
+ typeof(pcp) __ret, __old = *(ovalp); \
+ __ret = raw_cpu_cmpxchg(pcp, __old, nval); \
+ if (!likely(__ret == __old)) \
+ *(ovalp) = __ret; \
+ likely(__ret == __old); \
+})
+
#define __this_cpu_generic_read_nopreempt(pcp) \
({ \
typeof(pcp) ___ret; \
@@ -167,6 +176,15 @@ do { \
__ret; \
})

+#define this_cpu_generic_try_cmpxchg(pcp, ovalp, nval) \
+({ \
+ typeof(pcp) __ret, __old = *(ovalp); \
+ __ret = this_cpu_cmpxchg(pcp, __old, nval); \
+ if (!likely(__ret == __old)) \
+ *(ovalp) = __ret; \
+ likely(__ret == __old); \
+})
+
#ifndef raw_cpu_read_1
#define raw_cpu_read_1(pcp) raw_cpu_generic_read(pcp)
#endif
@@ -258,6 +276,36 @@ do { \
#define raw_cpu_xchg_8(pcp, nval) raw_cpu_generic_xchg(pcp, nval)
#endif

+#ifndef __SIZEOF_INT128__
+#define raw_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval) \
+({ \
+ typeof(pcp) *__p = raw_cpu_ptr(&(pcp)); \
+ typeof(pcp) __ret, __old = *(ovalp); \
+ bool __s; \
+ __ret = *__p; \
+ if (!__builtin_memcmp(&__ret, &__old, sizeof(pcp))) { \
+ *__p = nval; \
+ __s = true; \
+ } else { \
+ *(ovalp) = __ret; \
+ __s = false; \
+ } \
+ __s; \
+})
+
+#define raw_cpu_generic_cmpxchg_memcmp(pcp, oval, nval) \
+({ \
+ typeof(pcp) __old = (oval); \
+ raw_cpu_generic_try_cmpxchg_memcpy(pcp, &__old, nval); \
+ __old; \
+})
+
+#define raw_cpu_cmpxchg128(pcp, oval, nval) \
+ raw_cpu_generic_cmpxchg_memcmp(pcp, oval, nval)
+#define raw_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+ raw_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval)
+#endif
+
#ifndef raw_cpu_cmpxchg_1
#define raw_cpu_cmpxchg_1(pcp, oval, nval) \
raw_cpu_generic_cmpxchg(pcp, oval, nval)
@@ -283,6 +331,31 @@ do { \
raw_cpu_generic_cmpxchg(pcp, oval, nval)
#endif

+#ifndef raw_cpu_try_cmpxchg_1
+#define raw_cpu_try_cmpxchg_1(pcp, ovalp, nval) \
+ raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef raw_cpu_try_cmpxchg_2
+#define raw_cpu_try_cmpxchg_2(pcp, ovalp, nval) \
+ raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef raw_cpu_try_cmpxchg_4
+#define raw_cpu_try_cmpxchg_4(pcp, ovalp, nval) \
+ raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef raw_cpu_try_cmpxchg_8
+#define raw_cpu_try_cmpxchg_8(pcp, ovalp, nval) \
+ raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef raw_cpu_try_cmpxchg64
+#define raw_cpu_try_cmpxchg64(pcp, ovalp, nval) \
+ raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef raw_cpu_try_cmpxchg128
+#define raw_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+ raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+
#ifndef this_cpu_read_1
#define this_cpu_read_1(pcp) this_cpu_generic_read(pcp)
#endif
@@ -374,6 +447,33 @@ do { \
#define this_cpu_xchg_8(pcp, nval) this_cpu_generic_xchg(pcp, nval)
#endif

+#ifndef __SIZEOF_INT128__
+#define this_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval) \
+({ \
+ bool __ret; \
+ unsigned long __flags; \
+ raw_local_irq_save(__flags); \
+ __ret = raw_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval); \
+ raw_local_irq_restore(__flags); \
+ __ret; \
+})
+
+#define this_cpu_generic_cmpxchg_memcmp(pcp, oval, nval) \
+({ \
+ typeof(pcp) __ret; \
+ unsigned long __flags; \
+ raw_local_irq_save(__flags); \
+ __ret = raw_cpu_generic_cmpxchg_memcmp(pcp, oval, nval); \
+ raw_local_irq_restore(__flags); \
+ __ret; \
+})
+
+#define this_cpu_cmpxchg128(pcp, oval, nval) \
+ this_cpu_generic_cmpxchg_memcmp(pcp, oval, nval)
+#define this_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+ this_cpu_generic_try_cmpxchg_memcmp(pcp, ovalp, nval)
+#endif
+
#ifndef this_cpu_cmpxchg_1
#define this_cpu_cmpxchg_1(pcp, oval, nval) \
this_cpu_generic_cmpxchg(pcp, oval, nval)
@@ -399,4 +499,29 @@ do { \
this_cpu_generic_cmpxchg(pcp, oval, nval)
#endif

+#ifndef this_cpu_try_cmpxchg_1
+#define this_cpu_try_cmpxchg_1(pcp, ovalp, nval) \
+ this_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef this_cpu_try_cmpxchg_2
+#define this_cpu_try_cmpxchg_2(pcp, ovalp, nval) \
+ this_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef this_cpu_try_cmpxchg_4
+#define this_cpu_try_cmpxchg_4(pcp, ovalp, nval) \
+ this_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef this_cpu_try_cmpxchg_8
+#define this_cpu_try_cmpxchg_8(pcp, ovalp, nval) \
+ this_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef this_cpu_try_cmpxchg64
+#define this_cpu_try_cmpxchg64(pcp, ovalp, nval) \
+ this_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#ifndef this_cpu_try_cmpxchg128
+#define this_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+ this_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+
#endif /* _ASM_GENERIC_PERCPU_H_ */
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -13,6 +13,13 @@
#ifdef __SIZEOF_INT128__
typedef __s128 s128;
typedef __u128 u128;
+#else
+#ifdef CONFIG_64BIT
+/* hack for this_cpu_cmpxchg128 */
+typedef struct {
+ u64 a, b;
+} u128 __attribute__((aligned(16)));
+#endif
#endif

typedef u32 __kernel_dev_t;
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -11,14 +11,14 @@ void __init kmem_cache_init(void);
# define system_has_freelist_aba() system_has_cmpxchg128()
# define try_cmpxchg_freelist try_cmpxchg128
# endif
-#define this_cpu_cmpxchg_freelist this_cpu_cmpxchg128
+#define this_cpu_try_cmpxchg_freelist this_cpu_try_cmpxchg128
typedef u128 freelist_full_t;
#else /* CONFIG_64BIT */
# ifdef system_has_cmpxchg64
# define system_has_freelist_aba() system_has_cmpxchg64()
# define try_cmpxchg_freelist try_cmpxchg64
# endif
-#define this_cpu_cmpxchg_freelist this_cpu_cmpxchg64
+#define this_cpu_try_cmpxchg_freelist this_cpu_try_cmpxchg64
typedef u64 freelist_full_t;
#endif /* CONFIG_64BIT */

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3037,8 +3037,8 @@ __update_cpu_freelist_fast(struct kmem_c
freelist_aba_t old = { .freelist = freelist_old, .counter = tid };
freelist_aba_t new = { .freelist = freelist_new, .counter = next_tid(tid) };

- return this_cpu_cmpxchg_freelist(s->cpu_slab->freelist_tid.full,
- old.full, new.full) == old.full;
+ return this_cpu_try_cmpxchg_freelist(s->cpu_slab->freelist_tid.full,
+ &old.full, new.full);
}

/*