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SubjectRe: [block IO crash] Re: 2.6.39-rc5-git2 boot crashs
> So you have local irq disable/enable in both cases. So for the case
> where you don't have a local cmpxchg8b/16b available it's not worse
> versus irq disable/enable than now. It just has the possible repeat
> case when stuff changed between the prep and the actual cmpxchg, which
> is the same problem when cmpxchg8b/16 is available.

Right there is only the tid management that is added. Hope I am fast
enough to at least get one patch in (not very well tested):



Subject: slub: Remove CONFIG_CMPXCHG_LOCAL ifdeffery

Remove the #ifdefs. This means that the irqsafe_cpu_cmpxchg_double() is used
everywhere.

There may be performance implications since:

A. We now have to manage a transaction ID for all arches

B. The interrupt holdoff for arches not supporting CONFIG_CMPXCHG_LOCAL is reduced
to a very short irqoff section.

There are no multiple irqoff/irqon sequences as a result of this change. Even in the fallback
case we only have to do one disable and enable like before.

Signed-off-by: Christoph Lameter <cl@linux.com>

---
include/linux/slub_def.h | 2 -
mm/slub.c | 56 -----------------------------------------------
2 files changed, 58 deletions(-)
Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h 2011-05-04 09:33:08.000000000 -0500
+++ linux-2.6/include/linux/slub_def.h 2011-05-04 09:42:05.000000000 -0500
@@ -37,9 +37,7 @@ enum stat_item {

struct kmem_cache_cpu {
void **freelist; /* Pointer to next available object */
-#ifdef CONFIG_CMPXCHG_LOCAL
unsigned long tid; /* Globally unique transaction id */
-#endif
struct page *page; /* The slab from which we are allocating */
int node; /* The node of the page (or -1 for debug) */
#ifdef CONFIG_SLUB_STATS
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2011-05-04 09:41:59.000000000 -0500
+++ linux-2.6/mm/slub.c 2011-05-04 09:48:11.000000000 -0500
@@ -1540,7 +1540,6 @@ static void unfreeze_slab(struct kmem_ca
}
}

-#ifdef CONFIG_CMPXCHG_LOCAL
#ifdef CONFIG_PREEMPT
/*
* Calculate the next globally unique transaction for disambiguiation
@@ -1600,17 +1599,12 @@ static inline void note_cmpxchg_failure(
stat(s, CMPXCHG_DOUBLE_CPU_FAIL);
}

-#endif
-
void init_kmem_cache_cpus(struct kmem_cache *s)
{
-#ifdef CONFIG_CMPXCHG_LOCAL
int cpu;

for_each_possible_cpu(cpu)
per_cpu_ptr(s->cpu_slab, cpu)->tid = init_tid(cpu);
-#endif
-
}
/*
* Remove the cpu slab
@@ -1643,9 +1637,7 @@ static void deactivate_slab(struct kmem_
page->inuse--;
}
c->page = NULL;
-#ifdef CONFIG_CMPXCHG_LOCAL
c->tid = next_tid(c->tid);
-#endif
unfreeze_slab(s, page, tail);
}

@@ -1780,7 +1772,6 @@ static void *__slab_alloc(struct kmem_ca
{
void **object;
struct page *new;
-#ifdef CONFIG_CMPXCHG_LOCAL
unsigned long flags;

local_irq_save(flags);
@@ -1792,7 +1783,6 @@ static void *__slab_alloc(struct kmem_ca
*/
c = this_cpu_ptr(s->cpu_slab);
#endif
-#endif

/* We handle __GFP_ZERO in the caller */
gfpflags &= ~__GFP_ZERO;
@@ -1819,10 +1809,8 @@ load_freelist:
c->node = page_to_nid(c->page);
unlock_out:
slab_unlock(c->page);
-#ifdef CONFIG_CMPXCHG_LOCAL
c->tid = next_tid(c->tid);
local_irq_restore(flags);
-#endif
stat(s, ALLOC_SLOWPATH);
return object;

@@ -1858,9 +1846,7 @@ new_slab:
}
if (!(gfpflags & __GFP_NOWARN) && printk_ratelimit())
slab_out_of_memory(s, gfpflags, node);
-#ifdef CONFIG_CMPXCHG_LOCAL
local_irq_restore(flags);
-#endif
return NULL;
debug:
if (!alloc_debug_processing(s, c->page, object, addr))
@@ -1887,20 +1873,12 @@ static __always_inline void *slab_alloc(
{
void **object;
struct kmem_cache_cpu *c;
-#ifdef CONFIG_CMPXCHG_LOCAL
unsigned long tid;
-#else
- unsigned long flags;
-#endif

if (slab_pre_alloc_hook(s, gfpflags))
return NULL;

-#ifndef CONFIG_CMPXCHG_LOCAL
- local_irq_save(flags);
-#else
redo:
-#endif

/*
* Must read kmem_cache cpu data via this cpu ptr. Preemption is
@@ -1910,7 +1888,6 @@ redo:
*/
c = __this_cpu_ptr(s->cpu_slab);

-#ifdef CONFIG_CMPXCHG_LOCAL
/*
* The transaction ids are globally unique per cpu and per operation on
* a per cpu queue. Thus they can be guarantee that the cmpxchg_double
@@ -1919,7 +1896,6 @@ redo:
*/
tid = c->tid;
barrier();
-#endif

object = c->freelist;
if (unlikely(!object || !node_match(c, node)))
@@ -1927,7 +1903,6 @@ redo:
object = __slab_alloc(s, gfpflags, node, addr, c);

else {
-#ifdef CONFIG_CMPXCHG_LOCAL
/*
* The cmpxchg will only match if there was no additional
* operation and if we are on the right processor.
@@ -1948,16 +1923,9 @@ redo:
note_cmpxchg_failure("slab_alloc", s, tid);
goto redo;
}
-#else
- c->freelist = get_freepointer(s, object);
-#endif
stat(s, ALLOC_FASTPATH);
}

-#ifndef CONFIG_CMPXCHG_LOCAL
- local_irq_restore(flags);
-#endif
-
if (unlikely(gfpflags & __GFP_ZERO) && object)
memset(object, 0, s->objsize);

@@ -2034,11 +2002,9 @@ static void __slab_free(struct kmem_cach
{
void *prior;
void **object = (void *)x;
-#ifdef CONFIG_CMPXCHG_LOCAL
unsigned long flags;

local_irq_save(flags);
-#endif
slab_lock(page);
stat(s, FREE_SLOWPATH);

@@ -2070,9 +2036,7 @@ checks_ok:

out_unlock:
slab_unlock(page);
-#ifdef CONFIG_CMPXCHG_LOCAL
local_irq_restore(flags);
-#endif
return;

slab_empty:
@@ -2084,9 +2048,7 @@ slab_empty:
stat(s, FREE_REMOVE_PARTIAL);
}
slab_unlock(page);
-#ifdef CONFIG_CMPXCHG_LOCAL
local_irq_restore(flags);
-#endif
stat(s, FREE_SLAB);
discard_slab(s, page);
return;
@@ -2113,20 +2075,11 @@ static __always_inline void slab_free(st
{
void **object = (void *)x;
struct kmem_cache_cpu *c;
-#ifdef CONFIG_CMPXCHG_LOCAL
unsigned long tid;
-#else
- unsigned long flags;
-#endif

slab_free_hook(s, x);

-#ifndef CONFIG_CMPXCHG_LOCAL
- local_irq_save(flags);
-
-#else
redo:
-#endif

/*
* Determine the currently cpus per cpu slab.
@@ -2136,15 +2089,12 @@ redo:
*/
c = __this_cpu_ptr(s->cpu_slab);

-#ifdef CONFIG_CMPXCHG_LOCAL
tid = c->tid;
barrier();
-#endif

if (likely(page == c->page && c->node != NUMA_NO_NODE)) {
set_freepointer(s, object, c->freelist);

-#ifdef CONFIG_CMPXCHG_LOCAL
if (unlikely(!irqsafe_cpu_cmpxchg_double(
s->cpu_slab->freelist, s->cpu_slab->tid,
c->freelist, tid,
@@ -2153,16 +2103,10 @@ redo:
note_cmpxchg_failure("slab_free", s, tid);
goto redo;
}
-#else
- c->freelist = object;
-#endif
stat(s, FREE_FASTPATH);
} else
__slab_free(s, page, x, addr);

-#ifndef CONFIG_CMPXCHG_LOCAL
- local_irq_restore(flags);
-#endif
}

void kmem_cache_free(struct kmem_cache *s, void *x)

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