A debugfs file named `readahead' 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.
This is a trimmed down output on my PC:
# cat /debugfs/readahead
[table requests] total newfile state context contexta
cache_miss 234 50 10 54 0
read_random 116 37 4 21 0
io_congestion 0 0 0 0 0
io_cache_hit 61 0 14 37 0
io_block 4994 1576 232 120 2
readahead 1812 1522 171 107 2
lookahead 596 442 76 78 0
lookahead_hit 214 89 70 32 1
readahead_eof 1208 1080 95 21 2
readahead_shrink 0 0 0 0 0
readahead_thrash 0 0 0 0 0
readahead_rescue 1275 0 0 0 0
[table pages] total newfile state context contexta
cache_miss 401 98 50 87 0
read_random 120 37 4 21 0
io_congestion 0 0 0 0 0
io_cache_hit 872 0 412 448 0
io_block 22833 3857 12177 3680 21
readahead 15081 3827 9683 1484 21
readahead_hit 12684 3441 8164 1001 22
lookahead 8191 936 6926 329 0
lookahead_hit 8140 230 6368 1542 0
readahead_eof 5192 1955 2777 373 21
readahead_shrink 0 0 0 0 0
readahead_thrash 0 0 0 0 0
readahead_rescue 13656 0 0 0 0
[table summary] total newfile state context contexta
random_rate 6% 2% 2% 16% 0%
ra_hit_rate 84% 89% 84% 67% 100%
la_hit_rate 35% 20% 90% 40% 100%
avg_ra_size 8 3 56 14 7
avg_la_size 14 2 90 4 0
Signed-off-by: Wu Fengguang <[email protected]>
---
mm/readahead.c | 194 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 192 insertions(+), 2 deletions(-)
--- linux-2.6.14-rc5-mm1.orig/mm/readahead.c
+++ linux-2.6.14-rc5-mm1/mm/readahead.c
@@ -47,6 +47,9 @@ enum ra_class {
enum ra_event {
RA_EVENT_CACHE_MISS, /* read cache misses */
RA_EVENT_READRANDOM, /* random reads */
+ RA_EVENT_IO_CONGESTION, /* io congestion */
+ RA_EVENT_IO_CACHE_HIT, /* canceled io due to cache hit */
+ RA_EVENT_IO_BLOCK, /* read on locked page */
RA_EVENT_READAHEAD, /* read-ahead issued */
RA_EVENT_READAHEAD_HIT, /* read-ahead page hit */
@@ -65,6 +68,177 @@ enum ra_event {
*/
#define DEBUG_READAHEAD
#ifdef DEBUG_READAHEAD
+#include <linux/jiffies.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/init.h>
+
+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",
+ "readahead_eof",
+ "readahead_shrink",
+ "readahead_thrash",
+ "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 struct dentry *readahead_dentry;
+
+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_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,
+};
+
+static int __init readahead_init(void)
+{
+ readahead_dentry = debugfs_create_file("readahead",
+ 0644, NULL, NULL, &ra_debug_fops);
+ return 0;
+}
+
+module_init(readahead_init)
#define dprintk(args...) \
if (readahead_ratio & 1) printk(KERN_DEBUG args)
@@ -73,6 +247,10 @@ enum ra_event {
#else /* DEBUG_READAHEAD */
+static inline void ra_account(struct file_ra_state *ra,
+ enum ra_event e, int pages)
+{
+}
#define dprintk(args...) do {} while(0)
#define ddprintk(args...) do {} while(0)
@@ -945,6 +1123,8 @@ 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",
@@ -1577,8 +1757,11 @@ 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)
@@ -1665,8 +1848,15 @@ 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 (PageLocked(page))
+ ra_account(ra, RA_EVENT_IO_BLOCK,
+ ra->readahead_index - page->index);
+ } else {
+ if (PageLocked(page))
+ ra_account(0, RA_EVENT_IO_BLOCK, 1);
return;
+ }
ra->cache_hit++;
--
-
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