[PATCH 14/19] readahead: events accounting

[Wu Fengguang <wfg@mail.ustc.edu.cn>]

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A debugfs file named `readahead/events' is created according to advices from
J?rn Engel, Andrew Morton and Ingo Oeser. It yields to much better
readability than the preious /proc/vmstat interface :)

It reveals various read-ahead activities/events, and is vital to the testing.

-------------------------------------------------------------------------
If you are experiencing performance problems, or want to help improve the
read-ahead logic, please send me the debug data. Thanks.

- Preparations

## Compile with CONFIG_DEBUG_FS('Kernel hacking  --->  Debug Filesystem')
mkdir /debug
mount -t debug none /debug

- For each session with distinct access pattern

echo > /debug/readahead/events # reset the counters
# echo > /var/log/kern.log # you may want to backup it first
# echo 5 > /debug/readahead/debug_level # show verbose printk traces
## do one benchmark/task
# echo 0 > /debug/readahead/debug_level # revert to normal value
cp /debug/readahead/events readahead-events-`date +'%F_%R'`
# bzip2 -c /var/log/kern.log > kern.log-`date +'%F_%R'`.bz2

The commented out commands can uncover the very detailed file accesses,
which are useful sometimes. But the log file will be rather huge.

-------------------------------------------------------------------------
This is a trimmed down output on my PC:
# cat /debug/readahead/events
[table requests]      total    newfile      state    context      none
cache_miss              403         56         12         69       263
read_random             260         37          5         17       201
io_congestion             0          0          0          0         0
io_cache_hit             85          0         24         46         0
io_block               9796       5613        822        143      3203
readahead              5956       5418        383        139         0
lookahead               961        650        212         98         0
lookahead_hit           449        181        164         58        41
lookahead_ignore          0          0          0          0         0
readahead_eof          4981       4768        171         28         0
readahead_shrink          0          0          0          0         0
readahead_thrash          0          0          0          0         0
readahead_mutilt          0          0          0          0         0
readahead_rescue         45          0          0          0        45

[table pages]         total    newfile      state    context      none
cache_miss             5590         72       2506        181      2826
read_random             265         37          5         17       206
io_congestion             0          0          0          0         0
io_cache_hit           2440          0       1054       1366         0
io_block             165848      11117     147794       3668      3203
readahead             43080      11360      28949       2621         0
readahead_hit         38251      10716      25669       1818         9
lookahead             24013       1718      21641        647         0
lookahead_hit         20161        770      18679        712         0
lookahead_ignore          0          0          0          0         0
readahead_eof         15961       7924       7440        461         0
readahead_shrink          0          0          0          0         0
readahead_thrash          0          0          0          0         0
readahead_mutilt          0          0          0          0         0
readahead_rescue        240          0          0          0       240

[table summary]       total    newfile      state    context      none
random_rate              4%         0%         1%        10%       99%
ra_hit_rate             88%        94%        88%        69%      900%
la_hit_rate             46%        27%        76%        58%     4100%
avg_ra_size               7          2         75         19         0
avg_la_size              25          3        102          7         0

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

 mm/readahead.c |  194 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 192 insertions(+), 2 deletions(-)

--- linux-2.6.15-rc2-mm1.orig/mm/readahead.c
+++ linux-2.6.15-rc2-mm1/mm/readahead.c
@@ -105,6 +105,9 @@ enum ra_event {
 u32 readahead_debug_level = 0;
 u32 debug_disable_stateful_method = 0;
 
+static struct dentry *readahead_events_dentry;
+extern struct file_operations ra_debug_fops;
+
 static int __init readahead_init(void)
 {
 	struct dentry *root;
@@ -115,6 +118,9 @@ static int __init readahead_init(void)
 	debugfs_create_bool("disable_stateful_method", 0644, root,
 						&debug_disable_stateful_method);
 
+	readahead_events_dentry = debugfs_create_file("events",
+					0644, root, NULL, &ra_debug_fops);
+
 	return 0;
 }
 
@@ -132,6 +138,178 @@ static inline int disable_stateful_metho
 	return 0;
 }
 
+#endif
+
+/*
+ * Read-ahead events accounting.
+ */
+#ifdef DEBUG_READAHEAD
+
+static char *ra_class_name[] = {
+	"total",
+	"newfile",
+	"state",
+	"context",
+	"contexta",
+	"backward",
+	"onthrash",
+	"onraseek",
+	"none",
+};
+
+static char *ra_event_name[] = {
+	"cache_miss",
+	"read_random",
+	"io_congestion",
+	"io_cache_hit",
+	"io_block",
+	"readahead",
+	"readahead_hit",
+	"lookahead",
+	"lookahead_hit",
+	"lookahead_ignore",
+	"readahead_eof",
+	"readahead_shrink",
+	"readahead_thrash",
+	"readahead_mutilt",
+	"readahead_rescue",
+};
+
+static unsigned long ra_event_count[RA_CLASS_END+1][RA_EVENT_END][2];
+
+static inline void ra_account(struct file_ra_state *ra,
+				enum ra_event e, int pages)
+{
+	enum ra_class c;
+
+	c = (ra ? ra->flags & RA_CLASS_MASK : RA_CLASS_END);
+	if (e == RA_EVENT_READAHEAD_HIT && pages < 0) {
+		c = (ra->flags >> RA_CLASS_SHIFT) & RA_CLASS_MASK;
+		pages = -pages;
+	}
+	if (!c)
+		c = RA_CLASS_END;
+	BUG_ON(c > RA_CLASS_END);
+
+	ra_event_count[c][e][0] += 1;
+	ra_event_count[c][e][1] += pages;
+}
+
+static int ra_account_show(struct seq_file *s, void *_)
+{
+	int i;
+	int c;
+	int e;
+	static char event_fmt[] = "%-16s";
+	static char class_fmt[] = "%11s";
+	static char item_fmt[] = "%11lu";
+	static char percent_format[] = "%10lu%%";
+	static char *table_name[] = {
+		"[table requests]",
+		"[table pages]",
+		"[table summary]"};
+
+	for (i = 0; i <= 1; i++) {
+		for (e = 0; e < RA_EVENT_END; e++) {
+			ra_event_count[0][e][i] = 0;
+			for (c = 1; c <= RA_CLASS_END; c++)
+				ra_event_count[0][e][i] +=
+							ra_event_count[c][e][i];
+		}
+
+		seq_printf(s, event_fmt, table_name[i]);
+		for (c = 0; c <= RA_CLASS_END; c++)
+			seq_printf(s, class_fmt, ra_class_name[c]);
+		seq_puts(s, "\n");
+
+		for (e = 0; e < RA_EVENT_END; e++) {
+			if (e == RA_EVENT_READAHEAD_HIT && i == 0)
+				continue;
+
+			seq_printf(s, event_fmt, ra_event_name[e]);
+			for (c = 0; c <= RA_CLASS_END; c++)
+				seq_printf(s, item_fmt,
+						ra_event_count[c][e][i]);
+			seq_puts(s, "\n");
+		}
+		seq_puts(s, "\n");
+	}
+
+	seq_printf(s, event_fmt, table_name[2]);
+	for (c = 0; c <= RA_CLASS_END; c++)
+		seq_printf(s, class_fmt, ra_class_name[c]);
+	seq_puts(s, "\n");
+
+	seq_printf(s, event_fmt, "random_rate");
+	for (c = 0; c <= RA_CLASS_END; c++)
+		seq_printf(s, percent_format,
+			(ra_event_count[c][RA_EVENT_READRANDOM][0] * 100) /
+			(ra_event_count[c][RA_EVENT_READRANDOM][0] +
+			 ra_event_count[c][RA_EVENT_READAHEAD][0] + 1));
+	seq_puts(s, "\n");
+
+	seq_printf(s, event_fmt, "ra_hit_rate");
+	for (c = 0; c <= RA_CLASS_END; c++)
+		seq_printf(s, percent_format,
+			(ra_event_count[c][RA_EVENT_READAHEAD_HIT][1] * 100) /
+			(ra_event_count[c][RA_EVENT_READAHEAD][1] + 1));
+	seq_puts(s, "\n");
+
+	seq_printf(s, event_fmt, "la_hit_rate");
+	for (c = 0; c <= RA_CLASS_END; c++)
+		seq_printf(s, percent_format,
+			(ra_event_count[c][RA_EVENT_LOOKAHEAD_HIT][0] * 100) /
+			(ra_event_count[c][RA_EVENT_LOOKAHEAD][0] + 1));
+	seq_puts(s, "\n");
+
+	seq_printf(s, event_fmt, "avg_ra_size");
+	for (c = 0; c <= RA_CLASS_END; c++)
+		seq_printf(s, item_fmt,
+			(ra_event_count[c][RA_EVENT_READAHEAD][1] +
+			 ra_event_count[c][RA_EVENT_READAHEAD][0] / 2) /
+			(ra_event_count[c][RA_EVENT_READAHEAD][0] + 1));
+	seq_puts(s, "\n");
+
+	seq_printf(s, event_fmt, "avg_la_size");
+	for (c = 0; c <= RA_CLASS_END; c++)
+		seq_printf(s, item_fmt,
+			(ra_event_count[c][RA_EVENT_LOOKAHEAD][1] +
+			 ra_event_count[c][RA_EVENT_LOOKAHEAD][0] / 2) /
+			(ra_event_count[c][RA_EVENT_LOOKAHEAD][0] + 1));
+	seq_puts(s, "\n");
+
+	return 0;
+}
+
+static int ra_debug_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, ra_account_show, NULL);
+}
+
+static ssize_t ra_debug_write(struct file *file, const char __user *buf,
+				size_t size, loff_t *offset)
+{
+	if (file->f_dentry == readahead_events_dentry)
+		memset(ra_event_count, 0, sizeof(ra_event_count));
+	return 1;
+}
+
+static struct file_operations ra_debug_fops = {
+	.owner		= THIS_MODULE,
+	.open		= ra_debug_open,
+	.write		= ra_debug_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+#else /* !DEBUG_READAHEAD */
+
+static inline void ra_account(struct file_ra_state *ra,
+				enum ra_event e, int pages)
+{
+}
+
 #endif /* DEBUG_READAHEAD */
 
 
@@ -1024,6 +1202,8 @@ static int ra_dispatch(struct file_ra_st
 		ra_account(ra, RA_EVENT_READAHEAD_EOF, actual);
 	if (la_size)
 		ra_account(ra, RA_EVENT_LOOKAHEAD, la_size);
+	if (ra_size > actual)
+		ra_account(ra, RA_EVENT_IO_CACHE_HIT, ra_size - actual);
 	ra_account(ra, RA_EVENT_READAHEAD, actual);
 
 	dprintk("readahead-%s(ino=%lu, index=%lu, ra=%lu+%lu-%lu) = %d\n",
@@ -1668,8 +1848,11 @@ page_cache_readahead_adaptive(struct add
 	if (page) {
 		if(!TestClearPageReadahead(page))
 			return 0;
-		if (bdi_read_congested(mapping->backing_dev_info))
+		if (bdi_read_congested(mapping->backing_dev_info)) {
+			ra_account(ra, RA_EVENT_IO_CONGESTION,
+							end_index - index);
 			return 0;
+		}
 	}
 
 	if (page)
@@ -1759,8 +1942,15 @@ void fastcall ra_access(struct file_ra_s
 			   (1 << PG_referenced)))
 		return;
 
-	if (!ra_has_index(ra, page->index))
+	if (ra_has_index(ra, page->index)) {
+		if (!PageUptodate(page))
+			ra_account(ra, RA_EVENT_IO_BLOCK,
+					ra->readahead_index - page->index);
+	} else {
+		if (!PageUptodate(page))
+			ra_account(0, RA_EVENT_IO_BLOCK, 1);
 		return;
+	}
 
 	ra->cache_hit++;
 

--