Re: [RFC PATCH -tip 0/2 v3] pagecache tracepoints proposal

From: Wu Fengguang
Date: Mon Feb 08 2010 - 11:11:39 EST

Hi Ingo,

> Note that there's also these older experimental commits in tip:tracing/mm
> that introduce the notion of 'object collections' and adds the ability to
> trace them:
>
> 3383e37: tracing, page-allocator: Add a postprocessing script for page-allocator-related ftrace events
> c33b359: tracing, page-allocator: Add trace event for page traffic related to the buddy lists
> 0d524fb: tracing, mm: Add trace events for anti-fragmentation falling back to other migratetypes
> b9a2817: tracing, page-allocator: Add trace events for page allocation and page freeing
> 08b6cb8: perf_counter tools: Provide default bfd_demangle() function in case it's not around
> eb46710: tracing/mm: rename 'trigger' file to 'dump_range'
> 1487a7a: tracing/mm: fix mapcount trace record field
> dcac8cd: tracing/mm: add page frame snapshot trace
>
> this concept, if refreshed a bit and extended to the page cache, would allow
> the recording/snapshotting of the MM state of all currently present pages in
> the page-cache - a possibly nice addition to the dynamic technique you apply
> in your patches.
>
> there's similar "object collections" work underway for 'perf lock' btw., by
> Hitoshi Mitake and Frederic.
>
> So there's lots of common ground and lots of interest.

Here is a scratch patch to exercise the "object collections" idea :)

Interestingly, the pagecache walk is pretty fast, while copying out the trace
data takes more time:

# time (echo / > walk-fs)
(; echo / > walk-fs; ) 0.01s user 0.11s system 82% cpu 0.145 total

# time wc /debug/tracing/trace
4570 45893 551282 /debug/tracing/trace
wc /debug/tracing/trace 0.75s user 0.55s system 88% cpu 1.470 total

# time (cat /debug/tracing/trace > /dev/shm/t)
(; cat /debug/tracing/trace > /dev/shm/t; ) 0.04s user 0.49s system 95% cpu 0.548 total

# time (dd if=/debug/tracing/trace of=/dev/shm/t bs=1M)
0+138 records in
0+138 records out
551282 bytes (551 kB) copied, 0.380454 s, 1.4 MB/s
(; dd if=/debug/tracing/trace of=/dev/shm/t bs=1M; ) 0.09s user 0.48s system 96% cpu 0.600 total

The patch is based on tip/tracing/mm.

Thanks,
Fengguang
---
tracing: pagecache object collections

This dumps
- all cached files of a mounted fs (the inode-cache)
- all cached pages of a cached file (the page-cache)

Usage and Sample output:

# echo / > /debug/tracing/objects/mm/pages/walk-fs
# head /debug/tracing/trace

# tracer: nop
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
zsh-3078 [000] 526.272587: dump_inode: ino=102223 size=169291 cached=172032 age=9 dirty=6 dev=0:15 file=<TODO>
zsh-3078 [000] 526.274260: dump_pagecache_range: index=0 len=41 flags=10000000000002c count=1 mapcount=0
zsh-3078 [000] 526.274340: dump_pagecache_range: index=41 len=1 flags=10000000000006c count=1 mapcount=0
zsh-3078 [000] 526.274401: dump_inode: ino=8966 size=442 cached=4096 age=49 dirty=0 dev=0:15 file=<TODO>
zsh-3078 [000] 526.274425: dump_pagecache_range: index=0 len=1 flags=10000000000002c count=1 mapcount=0
zsh-3078 [000] 526.274440: dump_inode: ino=8964 size=4096 cached=0 age=49 dirty=0 dev=0:15 file=<TODO>

Here "age" is either age from inode create time, or from last dirty time.

TODO:

correctness
- show file path name
XXX: can trace_seq_path() be called directly inside TRACE_EVENT()?
- reliably prevent ring buffer overflow,
by replacing cond_resched() with some wait function
(eg. wait until 2+ pages are free in ring buffer)
- use stable_page_flags() in recent kernel

output style
- use plain tracing output format (no fancy TASK-PID/.../FUNCTION fields)
- clear ring buffer before dumping the objects?
- output format: key=value pairs ==> header + tabbed values?
- add filtering options if necessary

CC: Ingo Molnar <mingo@xxxxxxx>
CC: Chris Frost <frost@xxxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
fs/inode.c | 2
include/trace/events/mm.h | 67 ++++++++++++++
kernel/trace/trace_mm.c | 165 ++++++++++++++++++++++++++++++++++++
3 files changed, 233 insertions(+), 1 deletion(-)

--- linux-mm.orig/include/trace/events/mm.h 2010-02-08 23:19:09.000000000 +0800
+++ linux-mm/include/trace/events/mm.h 2010-02-08 23:19:16.000000000 +0800
@@ -2,6 +2,7 @@
#define _TRACE_MM_H

#include <linux/tracepoint.h>
+#include <linux/pagemap.h>
#include <linux/mm.h>

#undef TRACE_SYSTEM
@@ -42,6 +43,72 @@ TRACE_EVENT(dump_pages,
__entry->mapcount, __entry->index)
);

+TRACE_EVENT(dump_pagecache_range,
+
+ TP_PROTO(struct page *page, unsigned long len),
+
+ TP_ARGS(page, len),
+
+ TP_STRUCT__entry(
+ __field( unsigned long, index )
+ __field( unsigned long, len )
+ __field( unsigned long, flags )
+ __field( unsigned int, count )
+ __field( unsigned int, mapcount )
+ ),
+
+ TP_fast_assign(
+ __entry->index = page->index;
+ __entry->len = len;
+ __entry->flags = page->flags;
+ __entry->count = atomic_read(&page->_count);
+ __entry->mapcount = page_mapcount(page);
+ ),
+
+ TP_printk("index=%lu len=%lu flags=%lx count=%u mapcount=%u",
+ __entry->index,
+ __entry->len,
+ __entry->flags,
+ __entry->count,
+ __entry->mapcount)
+);
+
+TRACE_EVENT(dump_inode,
+
+ TP_PROTO(struct inode *inode),
+
+ TP_ARGS(inode),
+
+ TP_STRUCT__entry(
+ __field( unsigned long, ino )
+ __field( loff_t, size )
+ __field( unsigned long, nrpages )
+ __field( unsigned long, age )
+ __field( unsigned long, state )
+ __field( dev_t, dev )
+ ),
+
+ TP_fast_assign(
+ __entry->ino = inode->i_ino;
+ __entry->size = i_size_read(inode);
+ __entry->nrpages = inode->i_mapping->nrpages;
+ __entry->age = jiffies - inode->dirtied_when;
+ __entry->state = inode->i_state;
+ __entry->dev = inode->i_sb->s_dev;
+ ),
+
+ TP_printk("ino=%lu size=%llu cached=%lu age=%lu dirty=%lu "
+ "dev=%u:%u file=<TODO>",
+ __entry->ino,
+ __entry->size,
+ __entry->nrpages << PAGE_CACHE_SHIFT,
+ __entry->age / HZ,
+ __entry->state & I_DIRTY,
+ MAJOR(__entry->dev),
+ MINOR(__entry->dev))
+);
+
+
#endif /* _TRACE_MM_H */

/* This part must be outside protection */
--- linux-mm.orig/kernel/trace/trace_mm.c 2010-02-08 23:19:09.000000000 +0800
+++ linux-mm/kernel/trace/trace_mm.c 2010-02-08 23:19:16.000000000 +0800
@@ -9,6 +9,9 @@
#include <linux/bootmem.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
+#include <linux/pagevec.h>
+#include <linux/writeback.h>
+#include <linux/file.h>

#include "trace_output.h"

@@ -95,6 +98,162 @@ static const struct file_operations trac
.write = trace_mm_dump_range_write,
};

+static unsigned long page_flags(struct page* page)
+{
+ return page->flags & ((1 << NR_PAGEFLAGS) - 1);
+}
+
+static int pages_similiar(struct page* page0, struct page* page)
+{
+ if (page_count(page0) != page_count(page))
+ return 0;
+
+ if (page_mapcount(page0) != page_mapcount(page))
+ return 0;
+
+ if (page_flags(page0) != page_flags(page))
+ return 0;
+
+ return 1;
+}
+
+#define BATCH_LINES 100
+static void dump_pagecache(struct address_space *mapping)
+{
+ int i;
+ int lines = 0;
+ pgoff_t len = 0;
+ struct pagevec pvec;
+ struct page *page;
+ struct page *page0 = NULL;
+ unsigned long start = 0;
+
+ for (;;) {
+ pagevec_init(&pvec, 0);
+ pvec.nr = radix_tree_gang_lookup(&mapping->page_tree,
+ (void **)pvec.pages, start + len, PAGEVEC_SIZE);
+
+ if (pvec.nr == 0) {
+ if (len)
+ trace_dump_pagecache_range(page0, len);
+ break;
+ }
+
+ if (!page0)
+ page0 = pvec.pages[0];
+
+ for (i = 0; i < pvec.nr; i++) {
+ page = pvec.pages[i];
+
+ if (page->index == start + len &&
+ pages_similiar(page0, page))
+ len++;
+ else {
+ trace_dump_pagecache_range(page0, len);
+ page0 = page;
+ start = page->index;
+ len = 1;
+ if (++lines > BATCH_LINES) {
+ lines = 0;
+ cond_resched();
+ }
+ }
+ }
+ }
+}
+
+static void dump_fs_pagecache(struct super_block *sb)
+{
+ struct inode *inode;
+ struct inode *prev_inode = NULL;
+
+ down_read(&sb->s_umount);
+ if (!sb->s_root)
+ goto out;
+ spin_lock(&inode_lock);
+ list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
+ continue;
+ __iget(inode);
+ spin_unlock(&inode_lock);
+ trace_dump_inode(inode);
+ if (inode->i_mapping->nrpages)
+ dump_pagecache(inode->i_mapping);
+ iput(prev_inode);
+ prev_inode = inode;
+ cond_resched();
+ spin_lock(&inode_lock);
+ }
+ spin_unlock(&inode_lock);
+ iput(prev_inode);
+out:
+ up_read(&sb->s_umount);
+}
+
+static ssize_t
+trace_pagecache_write(struct file *filp, const char __user *ubuf, size_t count,
+ loff_t *ppos)
+{
+ struct file *file = NULL;
+ char *name;
+ int err = 0;
+
+ if (count > PATH_MAX + 1)
+ return -ENAMETOOLONG;
+
+ name = kmalloc(count+1, GFP_KERNEL);
+ if (!name)
+ return -ENOMEM;
+
+ if (copy_from_user(name, ubuf, count)) {
+ err = -EFAULT;
+ goto out;
+ }
+
+ /* strip the newline added by `echo` */
+ if (count)
+ name[count-1] = '\0';
+
+ file = filp_open(name, O_RDONLY|O_LARGEFILE, 0);
+ if (IS_ERR(file)) {
+ err = PTR_ERR(file);
+ file = NULL;
+ goto out;
+ }
+
+ if (tracing_update_buffers() < 0) {
+ err = -ENOMEM;
+ goto out;
+ }
+ if (trace_set_clr_event("mm", "dump_pagecache_range", 1)) {
+ err = -EINVAL;
+ goto out;
+ }
+ if (trace_set_clr_event("mm", "dump_inode", 1)) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ if (filp->f_path.dentry->d_inode->i_private) {
+ dump_fs_pagecache(file->f_path.dentry->d_sb);
+ } else {
+ dump_pagecache(file->f_mapping);
+ }
+
+out:
+ if (file)
+ fput(file);
+ kfree(name);
+
+ return err ? err : count;
+}
+
+static const struct file_operations trace_pagecache_fops = {
+ .open = tracing_open_generic,
+ .read = trace_mm_dump_range_read,
+ .write = trace_pagecache_write,
+};
+
/* move this into trace_objects.c when that file is created */
static struct dentry *trace_objects_dir(void)
{
@@ -167,6 +326,12 @@ static __init int trace_objects_mm_init(
trace_create_file("dump_range", 0600, d_pages, NULL,
&trace_mm_fops);

+ trace_create_file("walk-file", 0600, d_pages, NULL,
+ &trace_pagecache_fops);
+
+ trace_create_file("walk-fs", 0600, d_pages, (void *)1,
+ &trace_pagecache_fops);
+
return 0;
}
fs_initcall(trace_objects_mm_init);
--- linux-mm.orig/fs/inode.c 2010-02-08 23:19:12.000000000 +0800
+++ linux-mm/fs/inode.c 2010-02-08 23:19:22.000000000 +0800
@@ -149,7 +149,7 @@ struct inode *inode_init_always(struct s
inode->i_bdev = NULL;
inode->i_cdev = NULL;
inode->i_rdev = 0;
- inode->dirtied_when = 0;
+ inode->dirtied_when = jiffies;

if (security_inode_alloc(inode))
goto out_free_inode;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/