Re: [PATCH v3 08/11] slub: Replace cmpxchg

linux-parisc.vger.kernel.org archive mirror
 help / color / mirror / Atom feed

* 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

end of thread, other threads:[~2023-05-30 19:34 UTC | newest]

Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
     [not found] <20230515075659.118447996@infradead.org>
     [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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).