Collect readahead stats when CONFIG_READAHEAD_STATS=y.
This is enabled by default because the added overheads are trivial:
two readahead_stats() calls per readahead.
Example output:
(taken from a fresh booted NFS-ROOT box with rsize=16k)
$ cat /debug/readahead/stats
pattern readahead eof_hit cache_hit io sync_io mmap_io size async_size io_size
initial 524 216 26 498 498 18 7 4 4
subsequent 181 80 1 130 13 60 25 25 24
context 94 28 3 85 64 8 7 2 5
thrash 0 0 0 0 0 0 0 0 0
around 162 121 33 162 162 162 60 0 21
fadvise 0 0 0 0 0 0 0 0 0
random 137 0 0 137 137 0 1 0 1
all 1098 445 63 1012 874 0 17 6 9
The two most important columns are
- io number of readahead IO
- io_size average readahead IO size
CC: Ingo Molnar <mingo@xxxxxxx>
CC: Jens Axboe <jens.axboe@xxxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
mm/Kconfig | 13 +++
mm/readahead.c | 177 ++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 188 insertions(+), 2 deletions(-)
--- linux.orig/mm/readahead.c 2010-02-01 21:55:46.000000000 +0800
+++ linux/mm/readahead.c 2010-02-01 21:57:07.000000000 +0800
@@ -38,6 +38,179 @@ const char * const ra_pattern_names[] =
[RA_PATTERN_ALL] = "all",
};
+#ifdef CONFIG_READAHEAD_STATS
+#include <linux/seq_file.h>
+#include <linux/debugfs.h>
+enum ra_account {
+ /* number of readaheads */
+ RA_ACCOUNT_COUNT, /* readahead request */
+ RA_ACCOUNT_EOF, /* readahead request contains/beyond EOF page */
+ RA_ACCOUNT_CHIT, /* readahead request covers some cached pages */
+ RA_ACCOUNT_IOCOUNT, /* readahead IO */
+ RA_ACCOUNT_SYNC, /* readahead IO that is synchronous */
+ RA_ACCOUNT_MMAP, /* readahead IO by mmap accesses */
+ /* number of readahead pages */
+ RA_ACCOUNT_SIZE, /* readahead size */
+ RA_ACCOUNT_ASIZE, /* readahead async size */
+ RA_ACCOUNT_ACTUAL, /* readahead actual IO size */
+ /* end mark */
+ RA_ACCOUNT_MAX,
+};
+
+static unsigned long ra_stats[RA_PATTERN_MAX][RA_ACCOUNT_MAX];
+
+static void readahead_stats(struct address_space *mapping,
+ pgoff_t offset,
+ unsigned long req_size,
+ unsigned int ra_flags,
+ pgoff_t start,
+ unsigned int size,
+ unsigned int async_size,
+ int actual)
+{
+ unsigned int pattern = ra_pattern(ra_flags);
+
+ ra_stats[pattern][RA_ACCOUNT_COUNT]++;
+ ra_stats[pattern][RA_ACCOUNT_SIZE] += size;
+ ra_stats[pattern][RA_ACCOUNT_ASIZE] += async_size;
+ ra_stats[pattern][RA_ACCOUNT_ACTUAL] += actual;
+
+ if (actual < size) {
+ if (start + size >
+ (i_size_read(mapping->host) - 1) >> PAGE_CACHE_SHIFT)
+ ra_stats[pattern][RA_ACCOUNT_EOF]++;
+ else
+ ra_stats[pattern][RA_ACCOUNT_CHIT]++;
+ }
+
+ if (!actual)
+ return;
+
+ ra_stats[pattern][RA_ACCOUNT_IOCOUNT]++;
+
+ if (start <= offset && start + size > offset)
+ ra_stats[pattern][RA_ACCOUNT_SYNC]++;
+
+ if (ra_flags & READAHEAD_MMAP)
+ ra_stats[pattern][RA_ACCOUNT_MMAP]++;
+}
+
+static int readahead_stats_show(struct seq_file *s, void *_)
+{
+ unsigned long i;
+ unsigned long count, iocount;
+
+ seq_printf(s, "%-10s %10s %10s %10s %10s %10s %10s %10s %10s %10s\n",
+ "pattern",
+ "readahead", "eof_hit", "cache_hit",
+ "io", "sync_io", "mmap_io",
+ "size", "async_size", "io_size");
+
+ for (i = 0; i < RA_PATTERN_MAX; i++) {
+ count = ra_stats[i][RA_ACCOUNT_COUNT];
+ iocount = ra_stats[i][RA_ACCOUNT_IOCOUNT];
+ /*
+ * avoid division-by-zero
+ */
+ if (count == 0)
+ count = 1;
+ if (iocount == 0)
+ iocount = 1;
+
+ seq_printf(s, "%-10s %10lu %10lu %10lu %10lu %10lu %10lu "
+ "%10lu %10lu %10lu\n",
+ ra_pattern_names[i],
+ ra_stats[i][RA_ACCOUNT_COUNT],
+ ra_stats[i][RA_ACCOUNT_EOF],
+ ra_stats[i][RA_ACCOUNT_CHIT],
+ ra_stats[i][RA_ACCOUNT_IOCOUNT],
+ ra_stats[i][RA_ACCOUNT_SYNC],
+ ra_stats[i][RA_ACCOUNT_MMAP],
+ ra_stats[i][RA_ACCOUNT_SIZE] / count,
+ ra_stats[i][RA_ACCOUNT_ASIZE] / count,
+ ra_stats[i][RA_ACCOUNT_ACTUAL] / iocount);
+ }
+
+ return 0;
+}
+
+static int readahead_stats_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, readahead_stats_show, NULL);
+}
+
+static ssize_t readahead_stats_write(struct file *file, const char __user *buf,
+ size_t size, loff_t *offset)
+{
+ memset(ra_stats, 0, sizeof(ra_stats));
+ return size;
+}
+
+static struct file_operations readahead_stats_fops = {
+ .owner = THIS_MODULE,
+ .open = readahead_stats_open,
+ .write = readahead_stats_write,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+static struct dentry *ra_debug_root;
+
+static int debugfs_create_readahead(void)
+{
+ struct dentry *debugfs_stats;
+
+ ra_debug_root = debugfs_create_dir("readahead", NULL);
+ if (!ra_debug_root)
+ goto out;
+
+ debugfs_stats = debugfs_create_file("stats", 0644, ra_debug_root,
+ NULL, &readahead_stats_fops);
+ if (!debugfs_stats)
+ goto out;
+
+ return 0;
+out:
+ printk(KERN_ERR "readahead: failed to create debugfs entries\n");
+ return -ENOMEM;
+}
+
+static int __init readahead_init(void)
+{
+ debugfs_create_readahead();
+ return 0;
+}
+
+static void __exit readahead_exit(void)
+{
+ debugfs_remove_recursive(ra_debug_root);
+}
+
+module_init(readahead_init);
+module_exit(readahead_exit);
+#endif
+
+static void readahead_event(struct address_space *mapping,
+ pgoff_t offset,
+ unsigned long req_size,
+ unsigned int ra_flags,
+ pgoff_t start,
+ unsigned int size,
+ unsigned int async_size,
+ unsigned int actual)
+{
+#ifdef CONFIG_READAHEAD_STATS
+ readahead_stats(mapping, offset, req_size, ra_flags,
+ start, size, async_size, actual);
+ readahead_stats(mapping, offset, req_size,
+ RA_PATTERN_ALL << READAHEAD_PATTERN_SHIFT,
+ start, size, async_size, actual);
+#endif
+ trace_readahead(mapping, offset, req_size, ra_flags,
+ start, size, async_size, actual);
+}
+
/*
* Initialise a struct file's readahead state. Assumes that the caller has
* memset *ra to zero.
@@ -289,7 +462,7 @@ int force_page_cache_readahead(struct ad
nr_to_read -= this_chunk;
}
- trace_readahead(mapping, offset, nr_to_read,
+ readahead_event(mapping, offset, nr_to_read,
RA_PATTERN_FADVISE << READAHEAD_PATTERN_SHIFT,
offset, nr_to_read, 0, ret);
@@ -320,7 +493,7 @@ unsigned long ra_submit(struct file_ra_s
actual = __do_page_cache_readahead(mapping, filp,
ra->start, ra->size, ra->async_size);
- trace_readahead(mapping, offset, req_size, ra->ra_flags,
+ readahead_event(mapping, offset, req_size, ra->ra_flags,
ra->start, ra->size, ra->async_size, actual);
return actual;
--- linux.orig/mm/Kconfig 2010-02-01 21:55:28.000000000 +0800
+++ linux/mm/Kconfig 2010-02-01 21:55:49.000000000 +0800
@@ -283,3 +283,16 @@ config NOMMU_INITIAL_TRIM_EXCESS
of 1 says that all excess pages should be trimmed.
See Documentation/nommu-mmap.txt for more information.
+
+config READAHEAD_STATS
+ bool "Collect page-cache readahead stats"
+ depends on DEBUG_FS
+ default y
+ help
+ Enable readahead events accounting. Usage:
+
+ # mount -t debugfs none /debug
+
+ # echo > /debug/readahead/stats # reset counters
+ # do benchmarks
+ # cat /debug/readahead/stats # check counters
--
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