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Date: Fri, 12 Jun 2009 13:30:12 +0300 (EEST)
From: Pekka J Enberg <penberg@...helsinki.fi>
To: Nick Piggin <npiggin@...e.de>
cc: Ingo Molnar <mingo@...e.hu>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, benh@...nel.crashing.org,
akpm@...ux-foundation.org, cl@...ux-foundation.org,
torvalds@...ux-foundation.org
Subject: Re: [PATCH v2] slab,slub: ignore __GFP_WAIT if we're booting or
suspending
On Fri, 12 Jun 2009, Nick Piggin wrote:
> > Hi Ingo,
> >
> > On Fri, Jun 12, 2009 at 1:07 PM, Ingo Molnar<mingo@...e.hu> wrote:
> > > IMHO such invisible side-channels modifying the semantics of GFP
> > > flags is a bit dubious.
> > >
> > > We could do GFP_INIT or GFP_BOOT. These can imply other useful
> > > modifiers as well: panic-on-failure for example. (this would clean
> > > up a fair amount of init code that currently checks for an panics on
> > > allocation failure.)
> >
> > OK, but that means we need to fix up every single caller. I'm fine
> > with that but Ben is not. As I am unable to test powerpc here, I am
> > inclined to just merge Ben's patch as "obviously correct".
>
> I agree with Ingo though that exposing it as a gfp modifier is
> not so good. I just like the implementation to mask off GFP_WAIT
> better, and also prefer not to test system state, but have someone
> just call into slab to tell it not to unconditionally enable
> interrupts.
>
> > That does not mean we can't introduce GFP_BOOT later on if we want to. Hmm?
>
> Yes, with sufficient warnings in place, I don't think it should be
> too error prone to clean up remaining code over the course of
> a few releases.
Hmm. This is turning into one epic patch discussion for sure! But here's a
patch to do what you suggested. With the amount of patches I am
generating, I'm bound to hit the right one sooner or later, no?-)
Pekka
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 4880306..219b8fb 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -319,4 +319,6 @@ static inline void *kzalloc_node(size_t size, gfp_t flags, int node)
return kmalloc_node(size, flags | __GFP_ZERO, node);
}
+void __init kmem_cache_init_late(void);
+
#endif /* _LINUX_SLAB_H */
diff --git a/include/linux/slob_def.h b/include/linux/slob_def.h
index 0ec00b3..bb5368d 100644
--- a/include/linux/slob_def.h
+++ b/include/linux/slob_def.h
@@ -34,4 +34,9 @@ static __always_inline void *__kmalloc(size_t size, gfp_t flags)
return kmalloc(size, flags);
}
+static inline void kmem_cache_init_late(void)
+{
+ /* Nothing to do */
+}
+
#endif /* __LINUX_SLOB_DEF_H */
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index be5d40c..4dcbc2c 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -302,4 +302,6 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
}
#endif
+void __init kmem_cache_init_late(void);
+
#endif /* _LINUX_SLUB_DEF_H */
diff --git a/init/main.c b/init/main.c
index b3e8f14..f6204f7 100644
--- a/init/main.c
+++ b/init/main.c
@@ -640,6 +640,7 @@ asmlinkage void __init start_kernel(void)
"enabled early\n");
early_boot_irqs_on();
local_irq_enable();
+ kmem_cache_init_late();
/*
* HACK ALERT! This is early. We're enabling the console before
diff --git a/mm/slab.c b/mm/slab.c
index f46b65d..1fac378 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -304,6 +304,12 @@ struct kmem_list3 {
};
/*
+ * The slab allocator is initialized with interrupts disabled. Therefore, make
+ * sure early boot allocations don't accidentally enable interrupts.
+ */
+static gfp_t slab_gfp_mask __read_mostly = __GFP_BITS_MASK & ~__GFP_WAIT;
+
+/*
* Need this for bootstrapping a per node allocator.
*/
#define NUM_INIT_LISTS (3 * MAX_NUMNODES)
@@ -1654,6 +1660,14 @@ void __init kmem_cache_init(void)
*/
}
+void __init kmem_cache_init_late(void)
+{
+ /*
+ * Interrupts are enabled now so all GFP allocations are safe.
+ */
+ slab_gfp_mask = __GFP_BITS_MASK;
+}
+
static int __init cpucache_init(void)
{
int cpu;
@@ -3237,6 +3251,8 @@ retry:
}
if (!obj) {
+ local_flags &= slab_gfp_mask;
+
/*
* This allocation will be performed within the constraints
* of the current cpuset / memory policy requirements.
@@ -3354,12 +3370,14 @@ __cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
unsigned long save_flags;
void *ptr;
+ flags &= slab_gfp_mask;
+
lockdep_trace_alloc(flags);
if (slab_should_failslab(cachep, flags))
return NULL;
- cache_alloc_debugcheck_before(cachep, flags);
+ cache_alloc_debugcheck_before(cachep, flags & slab_gfp_flags);
local_irq_save(save_flags);
if (unlikely(nodeid == -1))
@@ -3434,6 +3452,8 @@ __cache_alloc(struct kmem_cache *cachep, gfp_t flags, void *caller)
unsigned long save_flags;
void *objp;
+ flags &= slab_gfp_flags;
+
lockdep_trace_alloc(flags);
if (slab_should_failslab(cachep, flags))
diff --git a/mm/slub.c b/mm/slub.c
index 3964d3c..c09cb98 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -178,6 +178,12 @@ static enum {
SYSFS /* Sysfs up */
} slab_state = DOWN;
+/*
+ * The slab allocator is initialized with interrupts disabled. Therefore, make
+ * sure early boot allocations don't accidentally enable interrupts.
+ */
+static gfp_t slab_gfp_mask __read_mostly = __GFP_BITS_MASK & ~__GFP_WAIT;
+
/* A list of all slab caches on the system */
static DECLARE_RWSEM(slub_lock);
static LIST_HEAD(slab_caches);
@@ -1595,6 +1601,8 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
unsigned long flags;
unsigned int objsize;
+ gfpflags &= slab_gfp_mask;
+
lockdep_trace_alloc(gfpflags);
might_sleep_if(gfpflags & __GFP_WAIT);
@@ -3104,6 +3112,14 @@ void __init kmem_cache_init(void)
nr_cpu_ids, nr_node_ids);
}
+void __init kmem_cache_init_late(void)
+{
+ /*
+ * Interrupts are enabled now so all GFP allocations are safe.
+ */
+ slab_gfp_mask = __GFP_BITS_MASK;
+}
+
/*
* Find a mergeable slab cache
*/
--
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