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Subject[RFC] Event counters [1/3]: Basic counter functionality
Light weight counter functions

The remaining counters in page_state after the zoned VM counter patch has been
applied are all just for show in /proc/vmstat. They have no essential function
for the VM and therefore we can make these counters lightweight by ignoring
races and also allow an off switch for embedded systems that allows a building
of a linux kernels without these counters.

The implementation of these counters is through inline code that typically
results in a simple increment of a global memory locations.

Also
- Rename page_state to event_state
- Make event state an array indexed by the event item.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.15-rc5-mm3/init/Kconfig
===================================================================
--- linux-2.6.15-rc5-mm3.orig/init/Kconfig 2005-12-16 11:44:09.000000000 -0800
+++ linux-2.6.15-rc5-mm3/init/Kconfig 2005-12-20 14:15:23.000000000 -0800
@@ -411,6 +411,15 @@ config SLAB
SLOB is more space efficient but does not scale well and is
more susceptible to fragmentation.

+config EVENT_COUNTERS
+ default y
+ bool "Enable event counters for /proc/vmstat" if EMBEDDED
+ help
+ Event counters are only needed to display statistics. They
+ have no function for the kernel itself. This option allows
+ the disabling of the event counters. /proc/vmstat will only
+ contain essential counters.
+
config SERIAL_PCI
depends PCI && SERIAL_8250
default y
Index: linux-2.6.15-rc5-mm3/include/linux/page-flags.h
===================================================================
--- linux-2.6.15-rc5-mm3.orig/include/linux/page-flags.h 2005-12-20 13:15:45.000000000 -0800
+++ linux-2.6.15-rc5-mm3/include/linux/page-flags.h 2005-12-20 14:55:00.000000000 -0800
@@ -77,120 +77,70 @@
#define PG_nosave_free 18 /* Free, should not be written */
#define PG_uncached 19 /* Page has been mapped as uncached */

+#ifdef CONFIG_EVENT_COUNTERS
/*
- * Global page accounting. One instance per CPU. Only unsigned longs are
- * allowed.
+ * Light weight per cpu counter implementation.
*
- * - Fields can be modified with xxx_page_state and xxx_page_state_zone at
- * any time safely (which protects the instance from modification by
- * interrupt.
- * - The __xxx_page_state variants can be used safely when interrupts are
- * disabled.
- * - The __xxx_page_state variants can be used if the field is only
- * modified from process context, or only modified from interrupt context.
- * In this case, the field should be commented here.
+ * Note that these can race. We do not bother to enable preemption
+ * or care about interrupt races. All we care about is to have some
+ * approximate count of events.
+ *
+ * Counters should only be incremented and no critical kernel component
+ * should rely on the counter values.
+ *
+ * Counters are handled completely inline. On many platforms the code
+ * generated will simply be the increment of a global address.
*/
-struct page_state {
- /*
- * The below are zeroed by get_page_state(). Use get_full_page_state()
- * to add up all these.
- */
- unsigned long pgpgin; /* Disk reads */
- unsigned long pgpgout; /* Disk writes */
- unsigned long pswpin; /* swap reads */
- unsigned long pswpout; /* swap writes */
-
- unsigned long pgalloc_high; /* page allocations */
- unsigned long pgalloc_normal;
- unsigned long pgalloc_dma32;
- unsigned long pgalloc_dma;
-
- unsigned long pgfree; /* page freeings */
- unsigned long pgactivate; /* pages moved inactive->active */
- unsigned long pgdeactivate; /* pages moved active->inactive */
-
- unsigned long pgfault; /* faults (major+minor) */
- unsigned long pgmajfault; /* faults (major only) */
-
- unsigned long pgrefill_high; /* inspected in refill_inactive_zone */
- unsigned long pgrefill_normal;
- unsigned long pgrefill_dma32;
- unsigned long pgrefill_dma;
-
- unsigned long pgsteal_high; /* total highmem pages reclaimed */
- unsigned long pgsteal_normal;
- unsigned long pgsteal_dma32;
- unsigned long pgsteal_dma;
-
- unsigned long pgscan_kswapd_high;/* total highmem pages scanned */
- unsigned long pgscan_kswapd_normal;
- unsigned long pgscan_kswapd_dma32;
- unsigned long pgscan_kswapd_dma;
-
- unsigned long pgscan_direct_high;/* total highmem pages scanned */
- unsigned long pgscan_direct_normal;
- unsigned long pgscan_direct_dma32;
- unsigned long pgscan_direct_dma;
-
- unsigned long pginodesteal; /* pages reclaimed via inode freeing */
- unsigned long slabs_scanned; /* slab objects scanned */
- unsigned long kswapd_steal; /* pages reclaimed by kswapd */
- unsigned long kswapd_inodesteal;/* reclaimed via kswapd inode freeing */
- unsigned long pageoutrun; /* kswapd's calls to page reclaim */
- unsigned long allocstall; /* direct reclaim calls */
+#define FOR_ALL_ZONES(x) x##_DMA, x##_DMA32, x##_NORMAL, x##_HIGH

- unsigned long pgrotated; /* pages rotated to tail of the LRU */
+enum event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
+ FOR_ALL_ZONES(PGALLOC),
+ PGFREE, PGACTIVATE, PGDEACTIVATE,
+ PGFAULT, PGMAJFAULT,
+ FOR_ALL_ZONES(PGREFILL),
+ FOR_ALL_ZONES(PGSTEAL),
+ FOR_ALL_ZONES(PGSCAN_KSWAPD),
+ FOR_ALL_ZONES(PGSCAN_DIRECT),
+ PGINODESTEAL, SLABS_SCANNED, KSWAPD_STEAL, KSWAPD_INODESTEAL,
+ PAGEOUTRUN, ALLOCSTALL, PGROTATED,
+ NR_EVENT_ITEMS
};

-extern void get_full_page_state(struct page_state *ret);
-extern unsigned long read_page_state_offset(unsigned long offset);
-extern void mod_page_state_offset(unsigned long offset, unsigned long delta);
-extern void __mod_page_state_offset(unsigned long offset, unsigned long delta);
-
-#define read_page_state(member) \
- read_page_state_offset(offsetof(struct page_state, member))
-
-#define mod_page_state(member, delta) \
- mod_page_state_offset(offsetof(struct page_state, member), (delta))
-
-#define __mod_page_state(member, delta) \
- __mod_page_state_offset(offsetof(struct page_state, member), (delta))
-
-#define inc_page_state(member) mod_page_state(member, 1UL)
-#define dec_page_state(member) mod_page_state(member, 0UL - 1)
-#define add_page_state(member,delta) mod_page_state(member, (delta))
-#define sub_page_state(member,delta) mod_page_state(member, 0UL - (delta))
-
-#define __inc_page_state(member) __mod_page_state(member, 1UL)
-#define __dec_page_state(member) __mod_page_state(member, 0UL - 1)
-#define __add_page_state(member,delta) __mod_page_state(member, (delta))
-#define __sub_page_state(member,delta) __mod_page_state(member, 0UL - (delta))
-
-#define page_state(member) (*__page_state(offsetof(struct page_state, member)))
-
-#define state_zone_offset(zone, member) \
-({ \
- unsigned offset; \
- if (is_highmem(zone)) \
- offset = offsetof(struct page_state, member##_high); \
- else if (is_normal(zone)) \
- offset = offsetof(struct page_state, member##_normal); \
- else if (is_dma32(zone)) \
- offset = offsetof(struct page_state, member##_dma32); \
- else \
- offset = offsetof(struct page_state, member##_dma); \
- offset; \
-})
-
-#define __mod_page_state_zone(zone, member, delta) \
- do { \
- __mod_page_state_offset(state_zone_offset(zone, member), (delta)); \
- } while (0)
-
-#define mod_page_state_zone(zone, member, delta) \
- do { \
- mod_page_state_offset(state_zone_offset(zone, member), (delta)); \
- } while (0)
+struct event_state {
+ unsigned long event[NR_EVENT_ITEMS];
+};
+
+DECLARE_PER_CPU(struct event_state, event_states);
+
+extern unsigned long get_global_events(enum event_item e);
+extern void sum_events(unsigned long *r, cpumask_t *cpumask);
+extern void all_events(unsigned long *r);
+
+static inline unsigned long get_cpu_events(enum event_item item)
+{
+ return __get_cpu_var(event_states).event[item];
+}
+
+static inline void count_event(enum event_item item)
+{
+ __get_cpu_var(event_states).event[item]++;
+}
+
+static inline void count_events(enum event_item item, long delta)
+{
+ __get_cpu_var(event_states).event[item] += delta;
+}
+
+#else
+/* Disable counters */
+#define get_cpu_events(e) 0L
+#define get_global_events(e) 0L
+#define count_event(e) do { } while (0)
+#define count_events(e,d) do { } while (0)
+#endif
+
+#define count_zone_event(item, zone) count_event(item##_DMA + zone_idx(zone))
+#define count_zone_events(item, zone, delta) count_events(item##_DMA + zone_idx(zone), delta)

/*
* Zone based accounting with per cpu differentials.
Index: linux-2.6.15-rc5-mm3/mm/page_alloc.c
===================================================================
--- linux-2.6.15-rc5-mm3.orig/mm/page_alloc.c 2005-12-20 14:14:33.000000000 -0800
+++ linux-2.6.15-rc5-mm3/mm/page_alloc.c 2005-12-20 15:46:46.000000000 -0800
@@ -1573,77 +1573,50 @@ static void show_node(struct zone *zone)
#define show_node(zone) do { } while (0)
#endif

-/*
- * Accumulate the page_state information across all CPUs.
- * The result is unavoidably approximate - it can change
- * during and after execution of this function.
- */
-static DEFINE_PER_CPU(struct page_state, page_states) = {0};
+#ifdef CONFIG_EVENT_COUNTERS
+DEFINE_PER_CPU(struct event_state, event_states) = {{0}};

-static void __get_page_state(struct page_state *ret, int nr, cpumask_t *cpumask)
+void sum_events(unsigned long *ret, cpumask_t *cpumask)
{
int cpu = 0;
+ int i;

- memset(ret, 0, sizeof(*ret));
+ memset(ret, 0, NR_EVENT_ITEMS * sizeof(unsigned long));

cpu = first_cpu(*cpumask);
while (cpu < NR_CPUS) {
- unsigned long *in, *out, off;
-
- in = (unsigned long *)&per_cpu(page_states, cpu);
+ struct event_state *this = &per_cpu(event_states, cpu);

cpu = next_cpu(cpu, *cpumask);

if (cpu < NR_CPUS)
- prefetch(&per_cpu(page_states, cpu));
+ prefetch(&per_cpu(event_states, cpu));
+

- out = (unsigned long *)ret;
- for (off = 0; off < nr; off++)
- *out++ += *in++;
+ for (i=0; i< NR_EVENT_ITEMS; i++)
+ ret[i] += this->event[i];
}
}
+EXPORT_SYMBOL(sum_events);

-void get_full_page_state(struct page_state *ret)
+void all_events(unsigned long *ret)
{
- cpumask_t mask = CPU_MASK_ALL;
-
- __get_page_state(ret, sizeof(*ret) / sizeof(unsigned long), &mask);
+ sum_events(ret, &cpu_online_map);
}
+EXPORT_SYMBOL(all_events);

-unsigned long read_page_state_offset(unsigned long offset)
+unsigned long get_global_events(enum event_item e)
{
unsigned long ret = 0;
int cpu;

- for_each_cpu(cpu) {
- unsigned long in;
+ for_each_cpu(cpu)
+ ret += per_cpu(event_states, cpu).event[e];

- in = (unsigned long)&per_cpu(page_states, cpu) + offset;
- ret += *((unsigned long *)in);
- }
return ret;
}
-
-void __mod_page_state_offset(unsigned long offset, unsigned long delta)
-{
- void *ptr;
-
- ptr = &__get_cpu_var(page_states);
- *(unsigned long *)(ptr + offset) += delta;
-}
-EXPORT_SYMBOL(__mod_page_state_offset);
-
-void mod_page_state_offset(unsigned long offset, unsigned long delta)
-{
- unsigned long flags;
- void *ptr;
-
- ptr = &__get_cpu_var(page_states);
- local_irq_save(flags);
- *(unsigned long *)(ptr + offset) += delta;
- local_irq_restore(flags);
-}
-EXPORT_SYMBOL(mod_page_state_offset);
+EXPORT_SYMBOL(get_global_events);
+#endif

void __get_zone_counts(unsigned long *active, unsigned long *inactive,
unsigned long *free, struct pglist_data *pgdat)
@@ -2663,7 +2636,7 @@ static char *vmstat_text[] = {
"nr_unstable",
"nr_bounce",

- /* Page state */
+#ifdef CONFIG_EVENT_COUNTERS
"pgpgin",
"pgpgout",
"pswpin",
@@ -2709,28 +2682,36 @@ static char *vmstat_text[] = {
"allocstall",

"pgrotated"
+#endif
};

static void *vmstat_start(struct seq_file *m, loff_t *pos)
{
unsigned long *v;
- struct page_state *ps;
+#ifdef CONFIG_EVENT_COUNTERS
+ unsigned long *e;
+#endif
int i;

if (*pos >= ARRAY_SIZE(vmstat_text))
return NULL;
-
+#ifdef CONFIG_EVENT_COUNTERS
v = kmalloc(NR_STAT_ITEMS * sizeof(unsigned long)
- + sizeof(struct page_state), GFP_KERNEL);
+ + sizeof(struct event_state), GFP_KERNEL);
+#else
+ v = kmalloc(NR_STAT_ITEMS * sizeof(unsigned long), GFP_KERNEL);
+#endif
m->private = v;
if (!v)
return ERR_PTR(-ENOMEM);
for (i = 0; i < NR_STAT_ITEMS; i++)
v[i] = global_page_state(i);
- ps = (struct page_state *)(v + NR_STAT_ITEMS);
- get_full_page_state(ps);
- ps->pgpgin /= 2; /* sectors -> kbytes */
- ps->pgpgout /= 2;
+#ifdef CONFIG_EVENT_COUNTERS
+ e = v + NR_STAT_ITEMS;
+ all_events(e);
+ e[PGPGIN] /= 2; /* sectors -> kbytes */
+ e[PGPGOUT] /= 2;
+#endif
return v + *pos;
}

-
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