Re: [PATCH 05/10] mm, page_alloc: Remove unnecessary updating of GFP flags during normal operation
From: Vlastimil Babka
Date: Tue Jul 28 2015 - 09:36:15 EST
On 07/20/2015 10:00 AM, Mel Gorman wrote:
From: Mel Gorman <mgorman@xxxxxxx>
During boot and suspend there is a restriction on the allowed GFP
flags. During boot it prevents blocking operations before the scheduler
is active. During suspend it is to avoid IO operations when storage is
unavailable. The restriction on the mask is applied in some allocator
hot-paths during normal operation which is wasteful. Use jump labels
to only update the GFP mask when it is restricted.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
[+CC Peterz, not trimmed due to that]
---
include/linux/gfp.h | 33 ++++++++++++++++++++++++++++-----
init/main.c | 2 +-
mm/page_alloc.c | 21 +++++++--------------
mm/slab.c | 4 ++--
mm/slob.c | 4 ++--
mm/slub.c | 6 +++---
6 files changed, 43 insertions(+), 27 deletions(-)
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index ad35f300b9a4..6d3a2d430715 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -394,12 +394,35 @@ static inline void page_alloc_init_late(void)
/*
* gfp_allowed_mask is set to GFP_BOOT_MASK during early boot to restrict what
- * GFP flags are used before interrupts are enabled. Once interrupts are
- * enabled, it is set to __GFP_BITS_MASK while the system is running. During
- * hibernation, it is used by PM to avoid I/O during memory allocation while
- * devices are suspended.
+ * GFP flags are used before interrupts are enabled. During hibernation, it is
+ * used by PM to avoid I/O during memory allocation while devices are suspended.
*/
-extern gfp_t gfp_allowed_mask;
+extern gfp_t __gfp_allowed_mask;
+
+/* Only update the gfp_mask when it is restricted */
+extern struct static_key gfp_restricted_key;
+
+static inline gfp_t gfp_allowed_mask(gfp_t gfp_mask)
+{
+ if (static_key_false(&gfp_restricted_key))
This is where it uses static_key_false()...
+ return gfp_mask;
+
+ return gfp_mask & __gfp_allowed_mask;
+}
+
+static inline void unrestrict_gfp_allowed_mask(void)
+{
+ WARN_ON(!static_key_enabled(&gfp_restricted_key));
+ __gfp_allowed_mask = __GFP_BITS_MASK;
+ static_key_slow_dec(&gfp_restricted_key);
+}
+
+static inline void restrict_gfp_allowed_mask(gfp_t gfp_mask)
+{
+ WARN_ON(static_key_enabled(&gfp_restricted_key));
+ __gfp_allowed_mask = gfp_mask;
+ static_key_slow_inc(&gfp_restricted_key);
+}
/* Returns true if the gfp_mask allows use of ALLOC_NO_WATERMARK */
bool gfp_pfmemalloc_allowed(gfp_t gfp_mask);
diff --git a/init/main.c b/init/main.c
index c5d5626289ce..7e3a227559c6 100644
--- a/init/main.c
+++ b/init/main.c
@@ -983,7 +983,7 @@ static noinline void __init kernel_init_freeable(void)
wait_for_completion(&kthreadd_done);
/* Now the scheduler is fully set up and can do blocking allocations */
- gfp_allowed_mask = __GFP_BITS_MASK;
+ unrestrict_gfp_allowed_mask();
/*
* init can allocate pages on any node
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7c2dc022f4ba..56432b59b797 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -124,7 +124,9 @@ unsigned long totalcma_pages __read_mostly;
unsigned long dirty_balance_reserve __read_mostly;
int percpu_pagelist_fraction;
-gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
+
+gfp_t __gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
+struct static_key gfp_restricted_key __read_mostly = STATIC_KEY_INIT_TRUE;
... and here it's combined with STATIC_KEY_INIT_TRUE. I've suspected
that this is not allowed, which Peter confirmed on IRC.
It's however true that the big comment at the top of
include/linux/jump_label.h only explicitly talks about combining
static_key_false() and static_key_true().
I'm not sure what's the correct idiom for a default-false static key
which however has to start as true on boot (Peter said such cases do
exist)...
#ifdef CONFIG_PM_SLEEP
/*
@@ -136,30 +138,21 @@ gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
* guaranteed not to run in parallel with that modification).
*/
-static gfp_t saved_gfp_mask;
-
void pm_restore_gfp_mask(void)
{
WARN_ON(!mutex_is_locked(&pm_mutex));
- if (saved_gfp_mask) {
- gfp_allowed_mask = saved_gfp_mask;
- saved_gfp_mask = 0;
- }
+ unrestrict_gfp_allowed_mask();
}
void pm_restrict_gfp_mask(void)
{
WARN_ON(!mutex_is_locked(&pm_mutex));
- WARN_ON(saved_gfp_mask);
- saved_gfp_mask = gfp_allowed_mask;
- gfp_allowed_mask &= ~GFP_IOFS;
+ restrict_gfp_allowed_mask(__GFP_BITS_MASK & ~GFP_IOFS);
}
bool pm_suspended_storage(void)
{
- if ((gfp_allowed_mask & GFP_IOFS) == GFP_IOFS)
- return false;
- return true;
+ return static_key_enabled(&gfp_restricted_key);
}
#endif /* CONFIG_PM_SLEEP */
@@ -2968,7 +2961,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
.migratetype = gfpflags_to_migratetype(gfp_mask),
};
- gfp_mask &= gfp_allowed_mask;
+ gfp_mask = gfp_allowed_mask(gfp_mask);
lockdep_trace_alloc(gfp_mask);
diff --git a/mm/slab.c b/mm/slab.c
index 200e22412a16..2c715b8c88f7 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3151,7 +3151,7 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
void *ptr;
int slab_node = numa_mem_id();
- flags &= gfp_allowed_mask;
+ flags = gfp_allowed_mask(flags);
lockdep_trace_alloc(flags);
@@ -3239,7 +3239,7 @@ slab_alloc(struct kmem_cache *cachep, gfp_t flags, unsigned long caller)
unsigned long save_flags;
void *objp;
- flags &= gfp_allowed_mask;
+ flags = gfp_allowed_mask(flags);
lockdep_trace_alloc(flags);
diff --git a/mm/slob.c b/mm/slob.c
index 4765f65019c7..23dbdac87fcb 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -430,7 +430,7 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
void *ret;
- gfp &= gfp_allowed_mask;
+ gfp = gfp_allowed_mask(gfp);
lockdep_trace_alloc(gfp);
@@ -536,7 +536,7 @@ static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
{
void *b;
- flags &= gfp_allowed_mask;
+ flags = gfp_allowed_mask(flags);
lockdep_trace_alloc(flags);
diff --git a/mm/slub.c b/mm/slub.c
index 816df0016555..9eb79f7a48ba 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1261,7 +1261,7 @@ static inline void kfree_hook(const void *x)
static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
gfp_t flags)
{
- flags &= gfp_allowed_mask;
+ flags = gfp_allowed_mask(flags);
lockdep_trace_alloc(flags);
might_sleep_if(flags & __GFP_WAIT);
@@ -1274,7 +1274,7 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
static inline void slab_post_alloc_hook(struct kmem_cache *s,
gfp_t flags, void *object)
{
- flags &= gfp_allowed_mask;
+ flags = gfp_allowed_mask(flags);
kmemcheck_slab_alloc(s, flags, object, slab_ksize(s));
kmemleak_alloc_recursive(object, s->object_size, 1, s->flags, flags);
memcg_kmem_put_cache(s);
@@ -1337,7 +1337,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
struct kmem_cache_order_objects oo = s->oo;
gfp_t alloc_gfp;
- flags &= gfp_allowed_mask;
+ flags = gfp_allowed_mask(flags);
if (flags & __GFP_WAIT)
local_irq_enable();
--
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