This is very useful for verifying whether the readahead algorithms are
working to the expectation.
Example output:
# echo 1 > /debug/tracing/events/vfs/readahead/enable
# cp test-file /dev/null
# cat /debug/tracing/trace # trimmed output
pattern=initial bdi=0:16 ino=100177 req=0+2 ra=0+4-2 async=0 actual=4
pattern=subsequent bdi=0:16 ino=100177 req=2+2 ra=4+8-8 async=1 actual=8
pattern=subsequent bdi=0:16 ino=100177 req=4+2 ra=12+16-16 async=1 actual=16
pattern=subsequent bdi=0:16 ino=100177 req=12+2 ra=28+32-32 async=1 actual=32
pattern=subsequent bdi=0:16 ino=100177 req=28+2 ra=60+60-60 async=1 actual=24
pattern=subsequent bdi=0:16 ino=100177 req=60+2 ra=120+60-60 async=1 actual=0
CC: Ingo Molnar <mingo@xxxxxxx>
CC: Jens Axboe <axboe@xxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Acked-by: Jan Kara <jack@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
fs/Makefile | 1
fs/trace.c | 2
include/trace/events/vfs.h | 77 +++++++++++++++++++++++++++++++++++
mm/readahead.c | 24 ++++++++++
4 files changed, 104 insertions(+)
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-next/include/trace/events/vfs.h 2012-01-25 15:57:52.000000000 +0800
@@ -0,0 +1,77 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM vfs
+
+#if !defined(_TRACE_VFS_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_VFS_H
+
+#include <linux/fs.h>
+#include <linux/blkdev.h>
+#include <linux/backing-dev.h>
+#include <linux/tracepoint.h>
+
+#define READAHEAD_PATTERNS \
+ { RA_PATTERN_INITIAL, "initial" }, \
+ { RA_PATTERN_SUBSEQUENT, "subsequent" }, \
+ { RA_PATTERN_CONTEXT, "context" }, \
+ { RA_PATTERN_MMAP_AROUND, "around" }, \
+ { RA_PATTERN_FADVISE, "fadvise" }, \
+ { RA_PATTERN_OVERSIZE, "oversize" }, \
+ { RA_PATTERN_RANDOM, "random" }, \
+ { RA_PATTERN_ALL, "all" }
+
+TRACE_EVENT(readahead,
+ TP_PROTO(struct address_space *mapping,
+ pgoff_t offset,
+ unsigned long req_size,
+ enum readahead_pattern pattern,
+ pgoff_t start,
+ unsigned long size,
+ unsigned long async_size,
+ unsigned int actual),
+
+ TP_ARGS(mapping, offset, req_size, pattern, start, size, async_size,
+ actual),
+
+ TP_STRUCT__entry(
+ __array(char, bdi, 32)
+ __field(ino_t, ino)
+ __field(pgoff_t, offset)
+ __field(unsigned long, req_size)
+ __field(unsigned int, pattern)
+ __field(pgoff_t, start)
+ __field(unsigned int, size)
+ __field(unsigned int, async_size)
+ __field(unsigned int, actual)
+ ),
+
+ TP_fast_assign(
+ strncpy(__entry->bdi,
+ dev_name(mapping->backing_dev_info->dev), 32);
+ __entry->ino = mapping->host->i_ino;
+ __entry->offset = offset;
+ __entry->req_size = req_size;
+ __entry->pattern = pattern;
+ __entry->start = start;
+ __entry->size = size;
+ __entry->async_size = async_size;
+ __entry->actual = actual;
+ ),
+
+ TP_printk("pattern=%s bdi=%s ino=%lu "
+ "req=%lu+%lu ra=%lu+%d-%d async=%d actual=%d",
+ __print_symbolic(__entry->pattern, READAHEAD_PATTERNS),
+ __entry->bdi,
+ __entry->ino,
+ __entry->offset,
+ __entry->req_size,
+ __entry->start,
+ __entry->size,
+ __entry->async_size,
+ __entry->start > __entry->offset,
+ __entry->actual)
+);
+
+#endif /* _TRACE_VFS_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
--- linux-next.orig/mm/readahead.c 2012-01-25 15:57:52.000000000 +0800
+++ linux-next/mm/readahead.c 2012-01-25 15:57:52.000000000 +0800
@@ -17,6 +17,7 @@
#include <linux/task_io_accounting_ops.h>
#include <linux/pagevec.h>
#include <linux/pagemap.h>
+#include <trace/events/vfs.h>
/*
* Initialise a struct file's readahead state. Assumes that the caller has
@@ -32,6 +33,21 @@ EXPORT_SYMBOL_GPL(file_ra_state_init);
#define list_to_page(head) (list_entry((head)->prev, struct page, lru))
+static inline void readahead_event(struct address_space *mapping,
+ pgoff_t offset,
+ unsigned long req_size,
+ bool for_mmap,
+ bool for_metadata,
+ enum readahead_pattern pattern,
+ pgoff_t start,
+ unsigned long size,
+ unsigned long async_size,
+ int actual)
+{
+ trace_readahead(mapping, offset, req_size,
+ pattern, start, size, async_size, actual);
+}
+
/*
* see if a page needs releasing upon read_cache_pages() failure
* - the caller of read_cache_pages() may have set PG_private or PG_fscache
@@ -228,6 +244,9 @@ int force_page_cache_readahead(struct ad
ret = err;
break;
}
+ readahead_event(mapping, offset, nr_to_read, 0, 0,
+ RA_PATTERN_FADVISE, offset, this_chunk, 0,
+ err);
ret += err;
offset += this_chunk;
nr_to_read -= this_chunk;
@@ -259,6 +278,11 @@ unsigned long ra_submit(struct file_ra_s
actual = __do_page_cache_readahead(mapping, filp,
ra->start, ra->size, ra->async_size);
+ readahead_event(mapping, offset, req_size,
+ ra->for_mmap, ra->for_metadata,
+ ra->pattern, ra->start, ra->size, ra->async_size,
+ actual);
+
ra->for_mmap = 0;
ra->for_metadata = 0;
return actual;
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-next/fs/trace.c 2012-01-25 15:57:52.000000000 +0800
@@ -0,0 +1,2 @@
+#define CREATE_TRACE_POINTS
+#include <trace/events/vfs.h>
--- linux-next.orig/fs/Makefile 2012-01-25 15:57:46.000000000 +0800
+++ linux-next/fs/Makefile 2012-01-25 15:57:52.000000000 +0800
@@ -50,6 +50,7 @@ obj-$(CONFIG_NFS_COMMON) += nfs_common/
obj-$(CONFIG_GENERIC_ACL) += generic_acl.o
obj-$(CONFIG_FHANDLE) += fhandle.o
+obj-$(CONFIG_TRACEPOINTS) += trace.o
obj-y += quota/
--
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