* Re: [PATCH v3 08/11] slub: Replace cmpxchg_double()
[not found] ` <20230524093246.GP83892@hirez.programming.kicks-ass.net>
@ 2023-05-30 14:22 ` Peter Zijlstra
2023-05-30 19:32 ` Peter Zijlstra
0 siblings, 1 reply; 2+ messages in thread
From: Peter Zijlstra @ 2023-05-30 14:22 UTC (permalink / raw)
To: torvalds
Cc: corbet, will, boqun.feng, mark.rutland, catalin.marinas, dennis,
tj, cl, hca, gor, agordeev, borntraeger, svens, tglx, mingo, bp,
dave.hansen, x86, hpa, joro, suravee.suthikulpanit, robin.murphy,
dwmw2, baolu.lu, Arnd Bergmann, Herbert Xu, davem, penberg,
rientjes, iamjoonsoo.kim, Andrew Morton, vbabka, roman.gushchin,
42.hyeyoo, linux-doc, linux-kernel, linux-mm, linux-s390, iommu,
linux-arch, linux-crypto, sfr, mpe, James.Bottomley, deller,
linux-parisc
On Wed, May 24, 2023 at 11:32:47AM +0200, Peter Zijlstra wrote:
> On Mon, May 15, 2023 at 09:57:07AM +0200, Peter Zijlstra wrote:
>
> > @@ -3008,6 +3029,22 @@ static inline bool pfmemalloc_match(stru
> > }
> >
> > #ifndef CONFIG_SLUB_TINY
> > +static inline bool
> > +__update_cpu_freelist_fast(struct kmem_cache *s,
> > + void *freelist_old, void *freelist_new,
> > + unsigned long tid)
> > +{
> > +#ifdef system_has_freelist_aba
> > + 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;
> > +#else
> > + return false;
> > +#endif
> > +}
> > +
> > /*
> > * Check the slab->freelist and either transfer the freelist to the
> > * per cpu freelist or deactivate the slab.
> > @@ -3359,11 +3396,7 @@ static __always_inline void *__slab_allo
> > * against code executing on this cpu *not* from access by
> > * other cpus.
> > */
> > - if (unlikely(!this_cpu_cmpxchg_double(
> > - s->cpu_slab->freelist, s->cpu_slab->tid,
> > - object, tid,
> > - next_object, next_tid(tid)))) {
> > -
> > + if (unlikely(!__update_cpu_freelist_fast(s, object, next_object, tid))) {
> > note_cmpxchg_failure("slab_alloc", s, tid);
> > goto redo;
> > }
> > @@ -3736,11 +3769,7 @@ static __always_inline void do_slab_free
> >
> > set_freepointer(s, tail_obj, freelist);
> >
> > - if (unlikely(!this_cpu_cmpxchg_double(
> > - s->cpu_slab->freelist, s->cpu_slab->tid,
> > - freelist, tid,
> > - head, next_tid(tid)))) {
> > -
> > + if (unlikely(!__update_cpu_freelist_fast(s, freelist, head, tid))) {
> > note_cmpxchg_failure("slab_free", s, tid);
> > goto redo;
> > }
>
> This isn't right; the this_cpu_cmpxchg_double() was unconditional and
> relied on the local_irq_save() fallback when no native cmpxchg128 is
> present.
This means this_cpu_cmpxchg128 is expected to be present on all 64bit
archs, except Mark just found out that HPPA doens't support __int128
until gcc-11.
(I've been building using gcc-12.2)
And because the cmpxchg128 fallback relies on '==' we can't trivally
fudge that with a struct type either :/ Now, afaict it all magically
works if I use:
#ifdef __SIZEOF_INT128__
typedef __s128 s128
typedef __u128 u128
#else
#if defined(CONFIG_PARISC) && defined(CONFIG_64BIT)
typedef long double u128;
#endif
#endif
but that is *super* gross.
The alternative is raising the minimum GCC for PARISC to gcc-11..
Yet another alternative is using a struct type and an equality function,
just for this.
Anybody?
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH v3 08/11] slub: Replace cmpxchg_double()
2023-05-30 14:22 ` [PATCH v3 08/11] slub: Replace cmpxchg_double() Peter Zijlstra
@ 2023-05-30 19:32 ` Peter Zijlstra
0 siblings, 0 replies; 2+ messages in thread
From: Peter Zijlstra @ 2023-05-30 19:32 UTC (permalink / raw)
To: torvalds
Cc: corbet, will, boqun.feng, mark.rutland, catalin.marinas, dennis,
tj, cl, hca, gor, agordeev, borntraeger, svens, tglx, mingo, bp,
dave.hansen, x86, hpa, joro, suravee.suthikulpanit, robin.murphy,
dwmw2, baolu.lu, Arnd Bergmann, Herbert Xu, davem, penberg,
rientjes, iamjoonsoo.kim, Andrew Morton, vbabka, roman.gushchin,
42.hyeyoo, linux-doc, linux-kernel, linux-mm, linux-s390, iommu,
linux-arch, linux-crypto, sfr, mpe, James.Bottomley, deller,
linux-parisc
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);
}
/*
^ permalink raw reply [flat|nested] 2+ messages in thread
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[not found] ` <20230515080554.453785148@infradead.org>
[not found] ` <20230524093246.GP83892@hirez.programming.kicks-ass.net>
2023-05-30 14:22 ` [PATCH v3 08/11] slub: Replace cmpxchg_double() Peter Zijlstra
2023-05-30 19:32 ` Peter Zijlstra
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