The flag is rarely enabled or even changed, so it's an ideal static key
candidate. Since it's being checked in the page allocator fastpath via
gfpflags_to_migratetype(), it may actually save some valuable cycles.
Here's a diff excerpt from __alloc_pages_nodemask() assembly:
-movl page_group_by_mobility_disabled(%rip), %ecx
+.byte 0x0f,0x1f,0x44,0x00,0
movl %r9d, %eax
shrl $3, %eax
andl $3, %eax
-testl %ecx, %ecx
-movl $0, %ecx
-cmovne %ecx, %eax
I.e. a NOP instead of test, conditional move and some assisting moves.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
include/linux/gfp.h | 2 +-
include/linux/mmzone.h | 3 ++-
mm/page_alloc.c | 23 +++++++++++++----------
3 files changed, 16 insertions(+), 12 deletions(-)
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index f8041f9de31e..097609342608 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -270,7 +270,7 @@ static inline int gfpflags_to_migratetype(const gfp_t gfp_flags)
BUILD_BUG_ON((1UL << GFP_MOVABLE_SHIFT) != ___GFP_MOVABLE);
BUILD_BUG_ON((___GFP_MOVABLE >> GFP_MOVABLE_SHIFT) != MIGRATE_MOVABLE);
- if (unlikely(page_group_by_mobility_disabled))
+ if (static_branch_unlikely(&page_group_by_mobility_disabled))
return MIGRATE_UNMOVABLE;
/* Group based on mobility */
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0f088f3a2fed..d1d440cff60e 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -17,6 +17,7 @@
#include <linux/pageblock-flags.h>
#include <linux/page-flags-layout.h>
#include <linux/atomic.h>
+#include <linux/jump_label.h>
#include <asm/page.h>
/* Free memory management - zoned buddy allocator. */
@@ -78,7 +79,7 @@ extern char * const migratetype_names[MIGRATE_TYPES];
for (order = 0; order < MAX_ORDER; order++) \
for (type = 0; type < MIGRATE_TYPES; type++)
-extern int page_group_by_mobility_disabled;
+extern struct static_key_false page_group_by_mobility_disabled;
#define NR_MIGRATETYPE_BITS (PB_migrate_end - PB_migrate + 1)
#define MIGRATETYPE_MASK ((1UL << NR_MIGRATETYPE_BITS) - 1)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6de9440e3ae2..655153ef8f2c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -281,7 +281,7 @@ EXPORT_SYMBOL(nr_node_ids);
EXPORT_SYMBOL(nr_online_nodes);
#endif
-int page_group_by_mobility_disabled __read_mostly;
+DEFINE_STATIC_KEY_FALSE(page_group_by_mobility_disabled);
#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
static inline void reset_deferred_meminit(pg_data_t *pgdat)
@@ -450,9 +450,10 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
void set_pageblock_migratetype(struct page *page, int migratetype)
{
- if (unlikely(page_group_by_mobility_disabled &&
- migratetype < MIGRATE_PCPTYPES))
- migratetype = MIGRATE_UNMOVABLE;
+ if (static_branch_unlikely(&page_group_by_mobility_disabled)) {
+ if (migratetype < MIGRATE_PCPTYPES)
+ migratetype = MIGRATE_UNMOVABLE;
+ }
set_pageblock_flags_group(page, (unsigned long)migratetype,
PB_migrate, PB_migrate_end);
@@ -1945,8 +1946,10 @@ static bool can_steal_fallback(unsigned int order, int start_mt)
if (order >= pageblock_order / 2 ||
start_mt == MIGRATE_RECLAIMABLE ||
- start_mt == MIGRATE_UNMOVABLE ||
- page_group_by_mobility_disabled)
+ start_mt == MIGRATE_UNMOVABLE)
+ return true;
+
+ if (static_branch_unlikely(&page_group_by_mobility_disabled))
return true;
return false;
@@ -1975,7 +1978,7 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
/* Claim the whole block if over half of it is free */
if (pages >= (1 << (pageblock_order-1)) ||
- page_group_by_mobility_disabled)
+ static_branch_unlikely(&page_group_by_mobility_disabled))
set_pageblock_migratetype(page, start_type);
}
@@ -4964,14 +4967,14 @@ void __ref build_all_zonelists(pg_data_t *pgdat, struct zone *zone)
* disabled and enable it later
*/
if (vm_total_pages < (pageblock_nr_pages * MIGRATE_TYPES))
- page_group_by_mobility_disabled = 1;
+ static_branch_enable(&page_group_by_mobility_disabled);
else
- page_group_by_mobility_disabled = 0;
+ static_branch_disable(&page_group_by_mobility_disabled);
pr_info("Built %i zonelists in %s order, mobility grouping %s. Total pages: %ld\n",
nr_online_nodes,
zonelist_order_name[current_zonelist_order],
- page_group_by_mobility_disabled ? "off" : "on",
+ static_key_enabled(&page_group_by_mobility_disabled) ? "off" : "on",
vm_total_pages);
#ifdef CONFIG_NUMA
pr_info("Policy zone: %s\n", zone_names[policy_zone]);
--
2.11.0
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