Re: [PATCH v3 1/5] add metadata_incore ioctl in vfs

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On Thu, Jan 20, 2011 at 12:10:14PM +0800, Andrew Morton wrote:
> On Thu, 20 Jan 2011 11:21:49 +0800 Shaohua Li <shaohua.li@xxxxxxxxx> wrote:
> 
> > > It seems to return a single offset/length tuple which refers to the
> > > btrfs metadata "file", with the intent that this tuple later be fed
> > > into a btrfs-specific readahead ioctl.
> > > 
> > > I can see how this might be used with say fatfs or ext3 where all
> > > metadata resides within the blockdev address_space.  But how is a
> > > filesytem which keeps its metadata in multiple address_spaces supposed
> > > to use this interface?
> > Oh, this looks like a big problem, thanks for letting me know such
> > filesystems. is it possible specific filesystem mapping multiple
> > address_space ranges to a virtual big ranges? the new ioctls handle the
> > mapping.
> 
> I'm not sure what you mean by that.
> 
> ext2, minix and probably others create an address_space for each
> directory.  Heaven knows what xfs does (for example).
> 
> > If the issue can't be solved, we can only add the metadata readahead for
> > specific implementation like my initial post instead of a generic
> > interface.
> 
> Well.  One approach would be for the kernel to report the names of all
> presently-cached files.  And for each file, report the offsets of all
> the pages which are presently in pagecache.  This all gets put into a
> database.
> 
> At cold-boot time we open all those files and read the relevant files.
> 
> To optimise that further, userspace would need to use fibmap to work
> out the LBA(s) of each page, and then read the pages in an optimised order.
> 
> To optimise that even further, userspace would need to find the on-disk
> locations all the metadata for each file, generate the metadata->data
> dependencies and then incorporate that into the reading order.
> 
> I actually wrote code to do all this.  Gad, it was ten years ago.  I
> forget how it works, but I do recall that it pioneered the technology
> of doing (effecticely) a sys_write(1, ...) from a kernel module, so the
> module's output appears on modprobe's stdout and can be redirected to
> another file or a pipe.  So sue me!  It's in
> http://userweb.kernel.org/~akpm/stuff/fboot.tar.gz.  Good luck with
> that ;)
> 
> <looks>
> 
> It walked mem_map[], indentifying pagecache pages, walking back from
> the page* all the way to the filename then logging the pathname and the
> file's pagecache indexes.  It also handled the blockdev superblock,
> where all the ext3 metadata resides.
 
> There are much smarter ways of doing this of course, especially with
> the vfs data structures which we later added.

Yup :) The attached patch walks sb->s_inodes and dumps a ordered view
of all cached file pages.  It will list each cached files and pages in
the order of the struct inode create time.

The patch will record and show the command name that first opened the
file.  (At the time we dump the page cache, the task may no longer
exists.) Although the field is very useful in some cases, it does add
runtime overheads.  I'm not sure how to balance this situation. Adding
a compile time option? But then the trace output becomes dependent on
kernel configuration, which may confuse user space tools (at least the
dumb ones).

Otherwise the patch is good enough for wider review.

Here is a trimmed example output.

root@bay /home/wfg# echo / > /debug/tracing/objects/mm/pages/dump-fs
root@bay /home/wfg# cat /debug/tracing/trace

The output are made of intermixed lines for inode and page. The
corresponding field names are:

file lines:
          ino         size       cached      age(ms) dirty type first-opened-by file-name

page lines:
       index    len  page-flags count mapcount 

      1507329         4096         8192       309042 ____  DIR          swapper /
           0      2 ____RU_____    1    0
      1786836        12288        40960       309026 ____  DIR          swapper /sbin
           0     10 ___ARU_____    1    0
      1786946        37312        40960       309024 ____  REG          swapper /sbin/init
           0      6 M__ARU_____    2    1
           6      1 M__A_U_____    2    1
           7      1 M__ARU_____    2    1
           8      2 _____U_____    1    0
      1507464            4         4096       309022 ____  LNK          swapper /lib64
           0      1 ___ARU_____    1    0
      1590173        12288            0       309021 ____  DIR          swapper /lib
      4563326           12         4096       309020 ____  LNK          swapper /lib/ld-linux-x86-64.so.2
           0      1 ___ARU_____    1    0
      4563295       128744       131072       309019 ____  REG          swapper /lib/ld-2.11.2.so
           0      1 M__ARU_____   21   20
           1      3 M__ARU_____   17   16
           4      4 M__ARU_____   20   19
           8      2 M__ARU_____   27   26
          10      3 M__ARU_____   20   19
          13      1 M__ARU_____   27   26
          14      1 M__ARU_____   26   25
          15      1 M__ARU_____   20   19
          16      1 M__ARU_____   18   17
          17      1 M__ARU_____    9    8
          18      1 M__A_U_____    4    3
          19      1 M__ARU_____   27   26
          20      1 M__ARU_____   17   16
          21      1 M__ARU_____   20   19
          22      1 M__ARU_____   27   26
          23      1 M__ARU_____   20   19
          24      1 M__ARU_____   26   25
          25      1 _____U_____    1    0
          26      1 M__A_U_____    4    3
          27      1 M__ARU_____   20   19
          28      4 _____U_____    1    0
      1525477        12288            0       309011 ____  DIR             init /etc
      1526463        64634        65536       309009 ____  REG             init /etc/ld.so.cache
           0      1 ___ARU_____    1    0
           1      1 _____U_____    1    0
           2     13 ___ARU_____    1    0
          15      1 ____RU_____    1    0
      1590258       241632       241664       309005 ____  REG             init /lib/libsepol.so.1
           0      5 M__ARU_____    2    1
           5     42 _____U_____    1    0
          47      1 M__ARU_____    2    1
          48     11 _____U_____    1    0
      1590330       117848       118784       308989 ____  REG             init /lib/libselinux.so.1
           0      1 M__ARU_____    7    6
           1      4 M__ARU_____    4    3
           5      1 M__ARU_____    5    4
           6      5 _____U_____    1    0
          11      2 M__ARU_____    4    3
          13      5 _____U_____    1    0
          18      1 ___ARU_____    1    0
          19      2 _____U_____    1    0
          21      1 M__ARU_____    5    4
          22      7 _____U_____    1    0
      4563314           14         4096       308982 ____  LNK             init /lib/libc.so.6
           0      1 ___ARU_____    1    0
      4563283      1432968      1433600       308981 ____  REG             init /lib/libc-2.11.2.so
           0      3 M__ARU_____   27   26
           3      1 M__ARU_____   25   24
           4      2 M__ARU_____   23   22
           6      1 M__ARU_____   26   25
           7      1 M__ARU_____   22   21
           8      1 M__ARU_____   27   26
           9      2 M__ARU_____   25   24
          11      1 M__ARU_____   23   22
          12      1 M__ARU_____   25   24
          13      1 M__ARU_____   24   23
          14      1 M__ARU_____   25   24
          15      3 M__ARU_____   24   23
          18      3 M__ARU_____   26   25
          21      2 M__ARU_____   27   26
          23      7 M__ARU_____   17   16
          30      1 M__ARU_____   29   28
          31      1 M__ARU_____   25   24
          32      2 M__ARU_____    4    3
          34      1 M__ARU_____    3    2
          35      2 M__ARU_____    4    3
          37      1 M__ARU_____    2    1
          38      1 _____U_____    1    0
          39      1 M__ARU_____    4    3
          40      1 M__ARU_____   13   12
          41      1 M__ARU_____   12   11
          42      1 M__ARU_____    5    4
          43      1 M__ARU_____   23   22
          44      2 M__ARU_____    6    5
          46      1 ___ARU_____    1    0
          47      1 M__ARU_____   12   11
          48      1 M__ARU_____    4    3
          49      1 M__ARU_____   18   17
          50      1 M__ARU_____   29   28
          51      2 M__ARU_____    2    1
          53      1 M__ARU_____   27   26
          54      1 M__ARU_____   19   18
          55      1 M__ARU_____   25   24
          56      2 _____U_____    1    0
          58      2 M__ARU_____    2    1
          60      2 _____U_____    1    0
          62      1 M__A_U_____    2    1
          63      1 _____U_____    1    0
          64      1 ___ARU_____    1    0
          65      3 M__ARU_____   29   28
          68      1 M__ARU_____   21   20
          69      1 M__ARU_____   26   25
          70      1 M__ARU_____    9    8
          71      1 M__ARU_____    3    2
          72      2 ___ARU_____    1    0
          74      2 _____U_____    1    0
          76      1 M__ARU_____   27   26
          77      2 M__ARU_____   13   12
          79      1 M__ARU_____    9    8
          80      1 M__ARU_____   10    9
          81      1 M__A_U_____    2    1
          82      1 M___RU_____    4    3
          83      1 M__ARU_____    3    2
          84      1 M__ARU_____   16   15
          85      1 M__ARU_____    3    2
          86     12 _____U_____    1    0
          98      1 M__ARU_____   26   25
          99      1 M__ARU_____   25   24
         100      2 M__ARU_____   17   16
         102      1 M__ARU_____   25   24
         103      1 M__ARU_____   18   17
         104      1 M__ARU_____   14   13
         105      3 _____U_____    1    0
         108      1 M__ARU_____   12   11
         109      2 M__ARU_____   26   25
         111      6 M__ARU_____   30   29
         117      1 M__ARU_____   29   28
         118      1 M__ARU_____   30   29
         119      1 M__ARU_____   19   18
         120      1 M__ARU_____   22   21
         121      1 M__ARU_____    3    2
         122      1 M__ARU_____   28   27
         123      1 M__ARU_____   30   29
         124      1 M__ARU_____   11   10
         125      1 M__ARU_____   26   25
         126      1 M__ARU_____   22   21
         127      2 M__ARU_____   29   28
         129      2 M__ARU_____    5    4
         131      1 M__ARU_____   10    9
         132      1 M__ARU_____   25   24
         133      2 M__ARU_____   17   16
         135      1 M__ARU_____    3    2
         136      6 _____U_____    1    0
         142      2 M__ARU_____    3    2
         144      1 M__ARU_____    8    7
         145      1 M__ARU_____   22   21
         146      3 M__ARU_____    8    7
         149      2 _____U_____    1    0
         151      3 M__ARU_____    6    5
         154      2 _____U_____    1    0
         156      1 M__ARU_____    8    7
         157      1 M__ARU_____   10    9
         158      1 M__ARU_____    9    8
         159      1 M__ARU_____    8    7
         160      1 M__ARU_____   28   27
         161      1 M__ARU_____   30   29
         162      1 M__ARU_____   14   13
         163      1 M____U_____    2    1
         164      2 _____U_____    1    0
         166      2 M__ARU_____    4    3
         168      1 M__ARU_____   12   11
         169      1 M__ARU_____   10    9
         170      1 M__ARU_____    4    3
         171      3 M__ARU_____    3    2
         174      6 ___ARU_____    1    0
         180      1 _____U_____    1    0
         181      9 ___ARU_____    1    0
         190      1 M__ARU_____    4    3
         191      1 ___A_U_____    1    0
         192      1 _____U_____    1    0
         193      1 ___A_U_____    1    0
         194      1 M__ARU_____   30   29
         195      1 M__ARU_____   27   26
         196      1 M__ARU_____   17   16
         197      2 _____U_____    1    0
         199      1 M__ARU_____   27   26
         200      1 M__ARU_____   25   24
         201      1 M__ARU_____    2    1
         202      1 M__ARU_____    9    8
         203      1 M__ARU_____   26   25
         204      1 M__ARU_____   14   13
         205      1 M__ARU_____    4    3
         206      1 M__ARU_____   18   17
         207      1 M__ARU_____   26   25
         208      1 M__ARU_____   22   21
         209      1 M__ARU_____    2    1
         210      1 M__ARU_____    3    2
         211      2 M____U_____    2    1
         213      5 _____U_____    1    0
         218      1 ___A_U_____    1    0

> <googles>
> 
> According to http://kerneltrap.org/node/2157 it sped up cold boot by
> "10%", whatever that means.  Seems that I wasn't sufficiently impressed
> by that and got distracted.
>
> I'm not sure any of that was very useful, really.  A full-on coldboot
> optimiser really wants visibility into every disk block which need to
> be read, and then mechanisms to tell the kernel to load those blocks
> into the correct address_spaces.  That's hard, because file data
> depends on file metadata.  A vast simplification would be to do it in
> two disk passes: read all the metadata on pass 1 then all the data on
> pass 2.

Yes, that is what this patchset tries to do.

> A totally different approach is to reorder all the data and metadata
> on-disk, so no special cold-boot processing is needed at all.

The boot time speedup mentioned in the changelog won't be possible
without the physical data/metadata reordering. Fortunately btrfs makes
it a trivial task.

> And a third approach is to save all the cache into a special
> file/partition/etc and to preload all that into kernel data structures
> at boot.  Obviously this one is ricky/tricky because the on-disk
> replica of the real data can get out of sync with the real data.

Hah! We are thinking much alike :)

It's a very good optimization for LiveCDs and readonly mounted NFS /usr.

For a typical desktop, the solution in my mind is to install some
initscript to run at halt/reboot time, after all other tasks have been
killed and filesystems remounted readonly.  At the time it may dump
whatever in the page cache to the swap partition. At the next boot,
the data/metadata can then be read back _perfectly sequentially_ for
populating the page cache.

For kexec based reboot, the data can even be passed to next kernel
directly, saving the disk IO totally.

Thanks,
Fengguang
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ mmotm/include/trace/events/mm.h	2010-12-26 20:59:48.000000000 +0800
@@ -0,0 +1,164 @@
+#if !defined(_TRACE_MM_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_MM_H
+
+#include <linux/tracepoint.h>
+#include <linux/page-flags.h>
+#include <linux/memcontrol.h>
+#include <linux/pagemap.h>
+#include <linux/mm.h>
+#include <linux/kernel-page-flags.h>
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM mm
+
+extern struct trace_print_flags pageflag_names[];
+
+/**
+ * dump_page_frame - called by the trace page dump trigger
+ * @pfn: page frame number
+ * @page: pointer to the page frame
+ *
+ * This is a helper trace point into the dumping of the page frames.
+ * It will record various infromation about a page frame.
+ */
+TRACE_EVENT(dump_page_frame,
+
+	TP_PROTO(unsigned long pfn, struct page *page),
+
+	TP_ARGS(pfn, page),
+
+	TP_STRUCT__entry(
+		__field(	unsigned long,	pfn		)
+		__field(	struct page *,	page		)
+		__field(	u64,		stable_flags	)
+		__field(	unsigned long,	flags		)
+		__field(	unsigned int,	count		)
+		__field(	unsigned int,	mapcount	)
+		__field(	unsigned long,	private		)
+		__field(	unsigned long,	mapping		)
+		__field(	unsigned long,	index		)
+	),
+
+	TP_fast_assign(
+		__entry->pfn		= pfn;
+		__entry->page		= page;
+		__entry->stable_flags	= stable_page_flags(page);
+		__entry->flags		= page->flags;
+		__entry->count		= atomic_read(&page->_count);
+		__entry->mapcount	= page_mapcount(page);
+		__entry->private	= page->private;
+		__entry->mapping	= (unsigned long)page->mapping;
+		__entry->index		= page->index;
+	),
+
+	TP_printk("%12lx %16p %8x %8x %16lx %16lx %16lx %s",
+		  __entry->pfn,
+		  __entry->page,
+		  __entry->count,
+		  __entry->mapcount,
+		  __entry->private,
+		  __entry->mapping,
+		  __entry->index,
+		  ftrace_print_flags_seq(p, "|",
+					 __entry->flags & PAGE_FLAGS_MASK,
+					 pageflag_names)
+	)
+);
+
+TRACE_EVENT(dump_page_cache,
+
+	TP_PROTO(struct page *page, unsigned long len),
+
+	TP_ARGS(page, len),
+
+	TP_STRUCT__entry(
+		__field(	unsigned long,	index		)
+		__field(	unsigned long,	len		)
+		__field(	u64,		flags		)
+		__field(	unsigned int,	count		)
+		__field(	unsigned int,	mapcount	)
+	),
+
+	TP_fast_assign(
+		__entry->index		= page->index;
+		__entry->len		= len;
+		__entry->flags		= stable_page_flags(page);
+		__entry->count		= atomic_read(&page->_count);
+		__entry->mapcount	= page_mapcount(page);
+	),
+
+	TP_printk("%12lu %6lu %c%c%c%c%c%c%c%c%c%c%c %4u %4u",
+		  __entry->index,
+		  __entry->len,
+		  __entry->flags & (1ULL << KPF_MMAP)		? 'M' : '_',
+		  __entry->flags & (1ULL << KPF_MLOCKED)	? 'm' : '_',
+		  __entry->flags & (1ULL << KPF_UNEVICTABLE)	? 'u' : '_',
+		  __entry->flags & (1ULL << KPF_ACTIVE)		? 'A' : '_',
+		  __entry->flags & (1ULL << KPF_REFERENCED)	? 'R' : '_',
+		  __entry->flags & (1ULL << KPF_UPTODATE)	? 'U' : '_',
+		  __entry->flags & (1ULL << KPF_DIRTY)		? 'D' : '_',
+		  __entry->flags & (1ULL << KPF_WRITEBACK)	? 'W' : '_',
+		  __entry->flags & (1ULL << KPF_RECLAIM)	? 'I' : '_',
+		  __entry->flags & (1ULL << KPF_MAPPEDTODISK)	? 'd' : '_',
+		  __entry->flags & (1ULL << KPF_PRIVATE)	? 'P' : '_',
+		  __entry->count,
+		  __entry->mapcount)
+);
+
+
+#define show_inode_type(val)	__print_symbolic(val, 	   \
+				{ S_IFREG,	"REG"	}, \
+				{ S_IFDIR,	"DIR"	}, \
+				{ S_IFLNK,	"LNK"	}, \
+				{ S_IFBLK,	"BLK"	}, \
+				{ S_IFCHR,	"CHR"	}, \
+				{ S_IFIFO,	"FIFO"	}, \
+				{ S_IFSOCK,	"SOCK"	})
+
+TRACE_EVENT(dump_inode_cache,
+
+	TP_PROTO(struct inode *inode, char *name, int len),
+
+	TP_ARGS(inode, name, len),
+
+	TP_STRUCT__entry(
+		__field(	unsigned long,	ino		)
+		__field(	loff_t,		size		) /* bytes */
+		__field(	loff_t,		cached		) /* bytes */
+		__field(	unsigned long,	age		) /*    ms */
+		__field(	unsigned long,	state		)
+		__field(	umode_t,	mode		)
+		__array(	char,		comm, TASK_COMM_LEN)
+		__dynamic_array(char,		file,	len	)
+	),
+
+	TP_fast_assign(
+		__entry->ino	= inode->i_ino;
+		__entry->size	= i_size_read(inode);
+		__entry->cached	= inode->i_mapping->nrpages;
+		__entry->cached	<<= PAGE_CACHE_SHIFT;
+		__entry->age	= (jiffies - inode->dirtied_when) * 1000 / HZ;
+		__entry->state	= inode->i_state;
+		__entry->mode	= inode->i_mode;
+		memcpy(__entry->comm, inode->i_comm, TASK_COMM_LEN);
+		memcpy(__get_str(file), name, len);
+	),
+
+	TP_printk("%12lu %12llu %12llu %12lu %c%c%c%c %4s %16s %s",
+		  __entry->ino,
+		  __entry->size,
+		  __entry->cached,
+		  __entry->age,
+		  __entry->state & I_DIRTY_PAGES	? 'D' : '_',
+		  __entry->state & I_DIRTY_DATASYNC	? 'd' : '_',
+		  __entry->state & I_DIRTY_SYNC		? 'm' : '_',
+		  __entry->state & I_SYNC		? 'S' : '_',
+		  show_inode_type(__entry->mode & S_IFMT),
+		  __entry->comm,
+		  __get_str(file))
+);
+
+#endif /*  _TRACE_MM_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
--- mmotm.orig/kernel/trace/Makefile	2010-12-26 20:58:46.000000000 +0800
+++ mmotm/kernel/trace/Makefile	2010-12-26 20:59:41.000000000 +0800
@@ -26,6 +26,7 @@ obj-$(CONFIG_RING_BUFFER) += ring_buffer
 obj-$(CONFIG_RING_BUFFER_BENCHMARK) += ring_buffer_benchmark.o
 
 obj-$(CONFIG_TRACING) += trace.o
+obj-$(CONFIG_TRACING) += trace_objects.o
 obj-$(CONFIG_TRACING) += trace_output.o
 obj-$(CONFIG_TRACING) += trace_stat.o
 obj-$(CONFIG_TRACING) += trace_printk.o
@@ -53,6 +54,7 @@ endif
 obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
 obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
 obj-$(CONFIG_EVENT_TRACING) += power-traces.o
+obj-$(CONFIG_EVENT_TRACING) += trace_mm.o
 ifeq ($(CONFIG_TRACING),y)
 obj-$(CONFIG_KGDB_KDB) += trace_kdb.o
 endif
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ mmotm/kernel/trace/trace_mm.c	2010-12-26 20:59:41.000000000 +0800
@@ -0,0 +1,367 @@
+/*
+ * Trace mm pages
+ *
+ * Copyright (C) 2009 Red Hat Inc, Steven Rostedt <srostedt@xxxxxxxxxx>
+ *
+ * Code based on Matt Mackall's /proc/[kpagecount|kpageflags] code.
+ */
+#include <linux/module.h>
+#include <linux/bootmem.h>
+#include <linux/debugfs.h>
+#include <linux/uaccess.h>
+#include <linux/ctype.h>
+#include <linux/pagevec.h>
+#include <linux/writeback.h>
+#include <linux/file.h>
+#include <linux/slab.h>
+
+#include "trace_output.h"
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/mm.h>
+
+void trace_mm_page_frames(unsigned long start, unsigned long end,
+			  void (*trace)(unsigned long pfn, struct page *page))
+{
+	unsigned long pfn = start;
+	struct page *page;
+
+	if (start > max_pfn - 1)
+		return;
+
+	if (end > max_pfn)
+		end = max_pfn;
+
+	while (pfn < end) {
+		page = NULL;
+		if (pfn_valid(pfn))
+			page = pfn_to_page(pfn);
+		pfn++;
+		if (page)
+			trace(pfn, page);
+	}
+}
+
+static void trace_mm_page_frame(unsigned long pfn, struct page *page)
+{
+	trace_dump_page_frame(pfn, page);
+}
+
+static ssize_t
+trace_mm_pfn_range_read(struct file *filp, char __user *ubuf, size_t cnt,
+			loff_t *ppos)
+{
+	return simple_read_from_buffer(ubuf, cnt, ppos, "0\n", 2);
+}
+
+
+/*
+ * recognized formats:
+ * 		"M N"	start=M, end=N
+ * 		"M"	start=M, end=M+1
+ * 		"M +N"	start=M, end=M+N-1
+ */
+static ssize_t
+trace_mm_pfn_range_write(struct file *filp, const char __user *ubuf, size_t cnt,
+			 loff_t *ppos)
+{
+	unsigned long start;
+	unsigned long end = 0;
+	char buf[64];
+	char *ptr;
+
+	if (cnt >= sizeof(buf))
+		return -EINVAL;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	if (tracing_update_buffers() < 0)
+		return -ENOMEM;
+
+	if (trace_set_clr_event("mm", "dump_page_frame", 1))
+		return -EINVAL;
+
+	buf[cnt] = 0;
+
+	start = simple_strtoul(buf, &ptr, 0);
+
+	for (; *ptr; ptr++) {
+		if (isdigit(*ptr)) {
+			if (*(ptr - 1) == '+')
+				end = start;
+			end += simple_strtoul(ptr, NULL, 0);
+			break;
+		}
+	}
+	if (!*ptr)
+		end = start + 1;
+
+	trace_mm_page_frames(start, end, trace_mm_page_frame);
+
+	return cnt;
+}
+
+static const struct file_operations trace_mm_fops = {
+	.open		= tracing_open_generic,
+	.read		= trace_mm_pfn_range_read,
+	.write		= trace_mm_pfn_range_write,
+};
+
+static struct dentry *trace_objects_mm_dir(void)
+{
+	static struct dentry *d_mm;
+	struct dentry *d_objects;
+
+	if (d_mm)
+		return d_mm;
+
+	d_objects = trace_objects_dir();
+	if (!d_objects)
+		return NULL;
+
+	d_mm = debugfs_create_dir("mm", d_objects);
+	if (!d_mm)
+		pr_warning("Could not create 'objects/mm' directory\n");
+
+	return d_mm;
+}
+
+static unsigned long page_flags(struct page *page)
+{
+	return page->flags & ((1 << NR_PAGEFLAGS) - 1);
+}
+
+static int pages_similar(struct page *page0, struct page *page)
+{
+	if (page_flags(page0) != page_flags(page))
+		return 0;
+
+	if (page_count(page0) != page_count(page))
+		return 0;
+
+	if (page_mapcount(page0) != page_mapcount(page))
+		return 0;
+
+	return 1;
+}
+
+static void dump_pagecache(struct address_space *mapping)
+{
+	unsigned long nr_pages;
+	struct page *pages[PAGEVEC_SIZE];
+	struct page *uninitialized_var(page0);
+	struct page *page;
+	unsigned long start = 0;
+	unsigned long len = 0;
+	int i;
+
+	for (;;) {
+		rcu_read_lock();
+		nr_pages = radix_tree_gang_lookup(&mapping->page_tree,
+				(void **)pages, start + len, PAGEVEC_SIZE);
+		rcu_read_unlock();
+
+		if (nr_pages == 0) {
+			if (len)
+				trace_dump_page_cache(page0, len);
+			return;
+		}
+
+		for (i = 0; i < nr_pages; i++) {
+			page = pages[i];
+
+			if (len &&
+			    page->index == start + len &&
+			    pages_similar(page0, page))
+				len++;
+			else {
+				if (len)
+					trace_dump_page_cache(page0, len);
+				page0 = page;
+				start = page->index;
+				len = 1;
+			}
+		}
+		cond_resched();
+	}
+}
+
+static void dump_inode_cache(struct inode *inode,
+			     char *name_buf,
+			     struct vfsmount *mnt)
+{
+	struct path path = {
+		.mnt = mnt,
+		.dentry = d_find_alias(inode)
+	};
+	char *name;
+	int len;
+
+	if (!mnt) {
+		trace_dump_inode_cache(inode, name_buf, strlen(name_buf));
+		return;
+	}
+
+	if (!path.dentry) {
+		trace_dump_inode_cache(inode, "", 1);
+		return;
+	}
+
+	name = d_path(&path, name_buf, PAGE_SIZE);
+	if (IS_ERR(name)) {
+		name = "";
+		len = 1;
+	} else
+		len = PAGE_SIZE + name_buf - name;
+
+	trace_dump_inode_cache(inode, name, len);
+
+	if (path.dentry)
+		dput(path.dentry);
+}
+
+static void dump_fs_pagecache(struct super_block *sb, struct vfsmount *mnt)
+{
+	struct inode *inode;
+	struct inode *prev_inode = NULL;
+	char *name_buf;
+
+	name_buf = (char *)__get_free_page(GFP_TEMPORARY);
+	if (!name_buf)
+		return;
+
+	down_read(&sb->s_umount);
+	if (!sb->s_root)
+		goto out;
+
+	spin_lock(&inode_lock);
+	list_for_each_entry_reverse(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);
+		dump_inode_cache(inode, name_buf, mnt);
+		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);
+	free_page((unsigned long)name_buf);
+}
+
+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 <= 1)
+		return -EINVAL;
+	if (count >= PAGE_SIZE)
+		return -ENAMETOOLONG;
+
+	name = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!name)
+		return -ENOMEM;
+
+	if (copy_from_user(name, ubuf, count)) {
+		err = -EFAULT;
+		goto out;
+	}
+
+	/* strip the newline added by `echo` */
+	if (name[count-1] == '\n')
+		name[count-1] = '\0';
+	else
+		name[count] = '\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_page_cache", 1)) {
+		err = -EINVAL;
+		goto out;
+	}
+	if (trace_set_clr_event("mm", "dump_inode_cache", 1)) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	if (filp->f_path.dentry->d_inode->i_private) {
+		dump_fs_pagecache(file->f_path.dentry->d_sb, file->f_path.mnt);
+	} else {
+		dump_inode_cache(file->f_mapping->host, name, NULL);
+		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_pfn_range_read,
+	.write		= trace_pagecache_write,
+};
+
+static struct dentry *trace_objects_mm_pages_dir(void)
+{
+	static struct dentry *d_pages;
+	struct dentry *d_mm;
+
+	if (d_pages)
+		return d_pages;
+
+	d_mm = trace_objects_mm_dir();
+	if (!d_mm)
+		return NULL;
+
+	d_pages = debugfs_create_dir("pages", d_mm);
+	if (!d_pages)
+		pr_warning("Could not create debugfs "
+			   "'objects/mm/pages' directory\n");
+
+	return d_pages;
+}
+
+static __init int trace_objects_mm_init(void)
+{
+	struct dentry *d_pages;
+
+	d_pages = trace_objects_mm_pages_dir();
+	if (!d_pages)
+		return 0;
+
+	trace_create_file("dump-pfn", 0600, d_pages, NULL,
+			  &trace_mm_fops);
+
+	trace_create_file("dump-file", 0600, d_pages, NULL,
+			  &trace_pagecache_fops);
+
+	trace_create_file("dump-fs", 0600, d_pages, (void *)1,
+			  &trace_pagecache_fops);
+
+	return 0;
+}
+fs_initcall(trace_objects_mm_init);
--- mmotm.orig/kernel/trace/trace.h	2010-12-26 20:58:46.000000000 +0800
+++ mmotm/kernel/trace/trace.h	2010-12-26 20:59:41.000000000 +0800
@@ -295,6 +295,7 @@ struct dentry *trace_create_file(const c
 				 const struct file_operations *fops);
 
 struct dentry *tracing_init_dentry(void);
+struct dentry *trace_objects_dir(void);
 
 struct ring_buffer_event;
 
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ mmotm/kernel/trace/trace_objects.c	2010-12-26 20:59:41.000000000 +0800
@@ -0,0 +1,26 @@
+#include <linux/debugfs.h>
+
+#include "trace.h"
+#include "trace_output.h"
+
+struct dentry *trace_objects_dir(void)
+{
+	static struct dentry *d_objects;
+	struct dentry *d_tracer;
+
+	if (d_objects)
+		return d_objects;
+
+	d_tracer = tracing_init_dentry();
+	if (!d_tracer)
+		return NULL;
+
+	d_objects = debugfs_create_dir("objects", d_tracer);
+	if (!d_objects)
+		pr_warning("Could not create debugfs "
+			   "'objects' directory\n");
+
+	return d_objects;
+}
+
+
--- mmotm.orig/mm/page_alloc.c	2010-12-26 20:58:46.000000000 +0800
+++ mmotm/mm/page_alloc.c	2010-12-26 20:59:41.000000000 +0800
@@ -5493,7 +5493,7 @@ bool is_free_buddy_page(struct page *pag
 }
 #endif
 
-static struct trace_print_flags pageflag_names[] = {
+struct trace_print_flags pageflag_names[] = {
 	{1UL << PG_locked,		"locked"	},
 	{1UL << PG_error,		"error"		},
 	{1UL << PG_referenced,		"referenced"	},
@@ -5541,7 +5541,7 @@ static void dump_page_flags(unsigned lon
 	printk(KERN_ALERT "page flags: %#lx(", flags);
 
 	/* remove zone id */
-	flags &= (1UL << NR_PAGEFLAGS) - 1;
+	flags &= PAGE_FLAGS_MASK;
 
 	for (i = 0; pageflag_names[i].name && flags; i++) {
 
--- mmotm.orig/include/linux/page-flags.h	2010-12-26 20:58:46.000000000 +0800
+++ mmotm/include/linux/page-flags.h	2010-12-26 20:59:41.000000000 +0800
@@ -414,6 +414,7 @@ static inline void __ClearPageTail(struc
  * there has been a kernel bug or struct page corruption.
  */
 #define PAGE_FLAGS_CHECK_AT_PREP	((1 << NR_PAGEFLAGS) - 1)
+#define PAGE_FLAGS_MASK			((1 << NR_PAGEFLAGS) - 1)
 
 #define PAGE_FLAGS_PRIVATE				\
 	(1 << PG_private | 1 << PG_private_2)
--- mmotm.orig/fs/inode.c	2010-12-26 20:58:45.000000000 +0800
+++ mmotm/fs/inode.c	2010-12-26 21:00:09.000000000 +0800
@@ -182,7 +182,13 @@ int inode_init_always(struct super_block
 	inode->i_bdev = NULL;
 	inode->i_cdev = NULL;
 	inode->i_rdev = 0;
-	inode->dirtied_when = 0;
+
+	/*
+	 * This records inode load time. It will be invalidated once inode is
+	 * dirtied, or jiffies wraps around. Despite the pitfalls it still
+	 * provides useful information for some use cases like fastboot.
+	 */
+	inode->dirtied_when = jiffies;
 
 	if (security_inode_alloc(inode))
 		goto out;
@@ -226,6 +232,9 @@ int inode_init_always(struct super_block
 
 	percpu_counter_inc(&nr_inodes);
 
+	BUILD_BUG_ON(sizeof(inode->i_comm) != TASK_COMM_LEN);
+	memcpy(inode->i_comm, current->comm, TASK_COMM_LEN);
+
 	return 0;
 out:
 	return -ENOMEM;
--- mmotm.orig/include/linux/fs.h	2010-12-26 20:59:50.000000000 +0800
+++ mmotm/include/linux/fs.h	2010-12-26 21:00:09.000000000 +0800
@@ -800,6 +800,8 @@ struct inode {
 	struct posix_acl	*i_default_acl;
 #endif
 	void			*i_private; /* fs or device private pointer */
+
+	char			i_comm[16]; /* first opened by */
 };
 
 static inline int inode_unhashed(struct inode *inode)

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