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Subject[PATCH 15/19] readahead: page aging accounting
The accuracy of stateful thrashing-threshold estimation depends largely on the
measurement of cold page aging speed.

A file named `page_aging' is created in debugfs to monitor the trace of two
measurement variables: per-zone `aging_total' and per-cpu `readahead_aging'.
Their values and the jiffies are recorded each time one of them has a delta
of 1, 1/2, 1/4, 1/16, 1/256, 1/4096 (nr_inactive + nr_free).

Sample series of collected data shows that smooth_aging is more stable in
small sampling granularity:

time dt page_aging8 smooth_aging8
872765 26 520056 33 653782 163
872791 12 520089 132 653945 51
872803 4 520221 132 653996 66
872807 17 520353 165 654062 107
872824 22 520518 99 654169 74
872846 372 520617 99 654243 78
873218 294 520716 99 654321 73
873512 196 520815 99 654394 130
873708 15 520914 231 654524 28
873723 15 521145 198 654552 9
873738 881 521343 99 654561 182
874619 700 521442 0 654743 198
875319 384 521442 66 654941 110
875703 2119 521508 99 655051 1632
877822 3960 521607 0 656683 980
881782 904 521607 0 657663 216

time dt page_aging1 smooth_aging1
-90822 12418 5775 12999 33302 10767
-78404 17510 18774 10303 44069 10345
-60894 24757 29077 9871 54414 14615
-36137 19194 38948 10404 69029 13726
-16943 19636 49352 10440 82755 12865
2693 16299 59792 12453 95620 10734
18992 19851 72245 10073 106354 15960
38843 16099 82318 10767 122314 14059
54942 16094 93085 10041 136373 12117
71036 19888 103126 12595 148490 16155
90924 18452 115721 9782 164645 11705
109376 22395 125503 10214 176350 13679
131771 19310 135717 10759 190029 11843
151081 20793 146476 10699 201872 12595
171874 22308 157175 10321 214467 13157
194182 17954 167496 10773 227624 14803
212136 19946 178269 10554 242427 13391
232082 21051 188823 11179 255818 11783

Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---

mm/readahead.c | 155 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 154 insertions(+), 1 deletion(-)

--- linux-2.6.15-rc1-mm2.orig/mm/readahead.c
+++ linux-2.6.15-rc1-mm2/mm/readahead.c
@@ -108,6 +108,9 @@ u32 debug_disable_stateful_method;
static struct dentry *readahead_events_dentry;
extern struct file_operations ra_debug_fops;

+static struct dentry *page_aging_dentry;
+extern struct file_operations aginginfo_fops;
+
static int __init readahead_init(void)
{
struct dentry *root;
@@ -120,6 +123,8 @@ static int __init readahead_init(void)

readahead_events_dentry = debugfs_create_file("events",
0644, root, NULL, &ra_debug_fops);
+ page_aging_dentry = debugfs_create_file("page_aging",
+ 0644, root, NULL, &aginginfo_fops);

return 0;
}
@@ -281,9 +286,14 @@ static int ra_account_show(struct seq_fi
return 0;
}

+extern struct seq_operations aginginfo_ops;
+
static int ra_debug_open(struct inode *inode, struct file *file)
{
- return single_open(file, ra_account_show, NULL);
+ if (file->f_dentry == readahead_events_dentry)
+ return single_open(file, ra_account_show, NULL);
+ else
+ return seq_open(file, &aginginfo_ops);
}

static ssize_t ra_debug_write(struct file *file, const char __user *buf,
@@ -312,6 +322,146 @@ static inline void ra_account(struct fil

#endif /* DEBUG_READAHEAD */

+/*
+ * Measure the aging progress of cold pages over time.
+ */
+#ifdef DEBUG_READAHEAD
+
+#define AGING_INFO_SIZE (1 << 8)
+#define AGING_INFO_MASK (AGING_INFO_SIZE - 1)
+static int aging_info_shift[] = {0, 1, 2, 4, 8, 12};
+#define AGING_INFO_SHIFTS (sizeof(aging_info_shift)/\
+ sizeof(aging_info_shift[0]))
+static int aging_info_index[AGING_INFO_SHIFTS];
+static unsigned long aging_info[AGING_INFO_SIZE][AGING_INFO_SHIFTS*3];
+static spinlock_t aging_info_lock = SPIN_LOCK_UNLOCKED;
+
+static unsigned long node_free_and_cold_pages(void);
+static unsigned long node_readahead_aging(void);
+
+/*
+ * The accumulated count of pages pushed into inactive_list(s).
+ */
+static unsigned long aging_total(void)
+{
+ unsigned int i;
+ unsigned long sum = 0;
+ struct zone *zones = NODE_DATA(numa_node_id())->node_zones;
+
+ for (i = 0; i < MAX_NR_ZONES; i++)
+ sum += zones[i].aging_total;
+
+ return sum;
+}
+
+static void collect_aging_info(void)
+{
+ int i;
+ unsigned long mem;
+ unsigned long page_aging;
+ unsigned long smooth_aging;
+
+ mem = node_free_and_cold_pages();
+ page_aging = aging_total();
+ smooth_aging = node_readahead_aging();
+
+ spin_lock_irq(&aging_info_lock);
+
+ for (i = AGING_INFO_SHIFTS - 1; i >= 0; i--) {
+ if (smooth_aging - aging_info[aging_info_index[i]][i*3+2] +
+ page_aging - aging_info[aging_info_index[i]][i*3+1] >
+ 2 * (mem >> aging_info_shift[i])) {
+ aging_info_index[i]++;
+ aging_info_index[i] &= AGING_INFO_MASK;
+ aging_info[aging_info_index[i]][i*3] = jiffies;
+ aging_info[aging_info_index[i]][i*3+1] = page_aging;
+ aging_info[aging_info_index[i]][i*3+2] = smooth_aging;
+ } else
+ break;
+ }
+
+ spin_unlock_irq(&aging_info_lock);
+}
+
+static void *aginginfo_start(struct seq_file *s, loff_t *pos)
+{
+ int n = *pos;
+ int i;
+
+ spin_lock_irq(&aging_info_lock);
+
+ if (!n) {
+ for (i = 0; i < AGING_INFO_SHIFTS; i++) {
+ seq_printf(s, "%12s %10s %18s%d %18s%d\t", "time","dt",
+ "page_aging", aging_info_shift[i],
+ "smooth_aging", aging_info_shift[i]);
+ }
+ seq_puts(s, "\n");
+ }
+
+ if (++n < AGING_INFO_SIZE)
+ return (void *)n;
+ else
+ return NULL;
+}
+
+static void *aginginfo_next(struct seq_file *s, void *p, loff_t *pos)
+{
+ int n = (int)p;
+
+ ++*pos;
+ return (void *)(++n < AGING_INFO_SIZE ? n : 0);
+}
+
+static void aginginfo_stop(struct seq_file *s, void *p)
+{
+ spin_unlock_irq(&aging_info_lock);
+}
+
+static int aginginfo_show(struct seq_file *s, void *p)
+{
+ int n = (int)p;
+ int i;
+ int index0;
+ int index1;
+ long time;
+ unsigned long nr1;
+ unsigned long nr2;
+
+ for (i = 0; i < AGING_INFO_SHIFTS; i++) {
+ index0 = aging_info_index[i] + n;
+ index1 = aging_info_index[i] + n + 1;
+ index0 &= AGING_INFO_MASK;
+ index1 &= AGING_INFO_MASK;
+ time = aging_info[index0][i*3];
+ nr1 = aging_info[index1][i*3+1] - aging_info[index0][i*3+1];
+ nr2 = aging_info[index1][i*3+2] - aging_info[index0][i*3+2];
+ seq_printf(s, "%12ld %10lu %10lu %8lu %10lu %8lu\t",
+ time, aging_info[index1][i*3] - time,
+ aging_info[index0][i*3+1], nr1,
+ aging_info[index0][i*3+2], nr2);
+ }
+ seq_puts(s, "\n");
+
+ return 0;
+}
+
+
+static struct seq_operations aginginfo_ops = {
+ .start = aginginfo_start,
+ .next = aginginfo_next,
+ .stop = aginginfo_stop,
+ .show = aginginfo_show,
+};
+
+static struct file_operations aginginfo_fops = {
+ .open = ra_debug_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
+#endif /* DEBUG_READAHEAD */

void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
@@ -1298,6 +1448,9 @@ static inline unsigned long compute_thra
else
*remain = 0;

+#ifdef DEBUG_READAHEAD
+ collect_aging_info();
+#endif
ddprintk("compute_thrashing_threshold: "
"ra=%lu=%lu*%lu/%lu, remain %lu for %lu\n",
ra_size, stream_shift, global_size, global_shift,
--
-
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