[PATCH v1 hot_track 00/18] vfs: hot data tracking

[PATCH v1 hot_track 00/18] vfs: hot data tracking

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

HI, guys,

  Any comments or ideas are appreciated, thanks.

NOTE:

  The patchset can be obtained via my kernel dev git on github:
git@github.com:wuzhy/kernel.git hot_tracking
  If you're interested, you can also review them via
https://github.com/wuzhy/kernel/commits/hot_tracking

  For more info, please check hot_tracking.txt in Documentation

TODO List:

 1.) Need to do scalability or performance tests. - Required
 2.) Need one simpler but efficient temp calculation function
 3.) How to save the file temperature among the umount to be able to
     preserve the file tempreture after reboot - Optional

Changelog:

 - Embed struct hot_type in struct file_system_type [Darrick J. Wong]
 - Cleanup Some issues [David Sterba]
 - Use a static hot debugfs root [Greg KH]
 - Rewritten debugfs support based on seq_file operation. [Dave Chinner]
 - Refactored workqueue support. [Dave Chinner]
 - Turn some Micro into be tunable   [Zhiyong, Zheng Liu]
       TIME_TO_KICK, and HEAT_UPDATE_DELAY
 - Introduce hot func registering framework [Zhiyong]
 - Remove global variable for hot tracking [Zhiyong]
 - Add xfs hot tracking support [Dave Chinner]
 - Add ext4 hot tracking support [Zheng Liu]
 - Cleanedup a lot of other issues [Dave Chinner]
 - Converted to Radix trees, not RB-tree [Zhiyong, Dave Chinner]
 - Added memory shrinker [Dave Chinner]
 - Converted to one workqueue to update map info periodically [Dave Chinner]
 - Cleanedup a lot of other issues [Dave Chinner]
 - Reduce new files and put all in fs/hot_tracking.[ch] [Dave Chinner]
 - Add btrfs hot tracking support [Zhiyong]
 - The first three patches can probably just be flattened into one.
                                        [Marco Stornelli , Dave Chinner]

Dave Chinner (1):
  xfs: add hot tracking support

Zheng Liu (1):
  ext4: add hot tracking support

Zhi Yong Wu (16):
  vfs: introduce some data structures
  vfs: add init and cleanup functions
  vfs: add I/O frequency update function
  vfs: add two map info arrays
  vfs: add hooks to enable hot tracking
  vfs: add temp calculation function
  vfs: add map info update function
  vfs: add aging function
  vfs: add one work queue
  vfs: add FS hot type support
  vfs: register one shrinker
  vfs: add one ioctl interface
  vfs: add debugfs support
  procfs: add two hot_track proc files
  btrfs: add hot tracking support
  vfs: add documentation

 Documentation/filesystems/00-INDEX         |    2 +
 Documentation/filesystems/hot_tracking.txt |  263 ++++++
 fs/Makefile                                |    2 +-
 fs/btrfs/ctree.h                           |    1 +
 fs/btrfs/super.c                           |   22 +-
 fs/compat_ioctl.c                          |    5 +
 fs/dcache.c                                |    2 +
 fs/direct-io.c                             |    6 +
 fs/ext4/ext4.h                             |    3 +
 fs/ext4/super.c                            |   13 +-
 fs/hot_tracking.c                          | 1321 ++++++++++++++++++++++++++++
 fs/hot_tracking.h                          |   53 ++
 fs/ioctl.c                                 |   74 ++
 fs/xfs/xfs_mount.h                         |    1 +
 fs/xfs/xfs_super.c                         |   16 +
 include/linux/fs.h                         |    5 +
 include/linux/hot_tracking.h               |  146 +++
 kernel/sysctl.c                            |   14 +
 mm/filemap.c                               |    6 +
 mm/page-writeback.c                        |   12 +
 mm/readahead.c                             |    7 +
 21 files changed, 1971 insertions(+), 3 deletions(-)
 create mode 100644 Documentation/filesystems/hot_tracking.txt
 create mode 100644 fs/hot_tracking.c
 create mode 100644 fs/hot_tracking.h
 create mode 100644 include/linux/hot_tracking.h

-- 
1.7.6.5

[PATCH v1 hot_track 01/18] vfs: introduce some data structures

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  One root structure hot_info is defined, is hooked
up in super_block, and will be used to hold radix tree
root, hash list root and some other information, etc.
  Adds hot_inode_tree struct to keep track of
frequently accessed files, and be keyed by {inode, offset}.
Trees contain hot_inode_items representing those files
and ranges.
  Having these trees means that vfs can quickly determine the
temperature of some data by doing some calculations on the
hot_freq_data struct that hangs off of the tree item.
  Define two items hot_inode_item and hot_range_item,
one of them represents one tracked file
to keep track of its access frequency and the tree of
ranges in this file, while the latter represents
a file range of one inode.
  Each of the two structures contains a hot_freq_data
struct with its frequency of access metrics (number of
{reads, writes}, last {read,write} time, frequency of
{reads,writes}).
  Also, each hot_inode_item contains one hot_range_tree
struct which is keyed by {inode, offset, length}
and used to keep track of all the ranges in this file.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/Makefile                  |    2 +-
 fs/dcache.c                  |    2 +
 fs/hot_tracking.c            |  109 ++++++++++++++++++++++++++++++++++++++++++
 fs/hot_tracking.h            |   23 +++++++++
 include/linux/hot_tracking.h |   73 ++++++++++++++++++++++++++++
 5 files changed, 208 insertions(+), 1 deletions(-)
 create mode 100644 fs/hot_tracking.c
 create mode 100644 fs/hot_tracking.h
 create mode 100644 include/linux/hot_tracking.h

diff --git a/fs/Makefile b/fs/Makefile
index 1d7af79..f966dea 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -11,7 +11,7 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		attr.o bad_inode.o file.o filesystems.o namespace.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
 		pnode.o drop_caches.o splice.o sync.o utimes.o \
-		stack.o fs_struct.o statfs.o
+		stack.o fs_struct.o statfs.o hot_tracking.o
 
 ifeq ($(CONFIG_BLOCK),y)
 obj-y +=	buffer.o bio.o block_dev.o direct-io.o mpage.o ioprio.o
diff --git a/fs/dcache.c b/fs/dcache.c
index 3a463d0..7d5be16 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -37,6 +37,7 @@
 #include <linux/rculist_bl.h>
 #include <linux/prefetch.h>
 #include <linux/ratelimit.h>
+#include <linux/hot_tracking.h>
 #include "internal.h"
 #include "mount.h"
 
@@ -3172,4 +3173,5 @@ void __init vfs_caches_init(unsigned long mempages)
 	mnt_init();
 	bdev_cache_init();
 	chrdev_init();
+	hot_cache_init();
 }
diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
new file mode 100644
index 0000000..806fbb0
--- /dev/null
+++ b/fs/hot_tracking.c
@@ -0,0 +1,109 @@
+/*
+ * fs/hot_tracking.c
+ *
+ * Copyright (C) 2012 IBM Corp. All rights reserved.
+ * Written by Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ */
+
+#include <linux/list.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/hardirq.h>
+#include <linux/fs.h>
+#include <linux/blkdev.h>
+#include <linux/types.h>
+#include <linux/limits.h>
+#include "hot_tracking.h"
+
+/* kmem_cache pointers for slab caches */
+static struct kmem_cache *hot_inode_item_cachep __read_mostly;
+static struct kmem_cache *hot_range_item_cachep __read_mostly;
+
+/*
+ * Initialize the inode tree. Should be called for each new inode
+ * access or other user of the hot_inode interface.
+ */
+static void hot_inode_tree_init(struct hot_info *root)
+{
+	INIT_RADIX_TREE(&root->hot_inode_tree, GFP_ATOMIC);
+	spin_lock_init(&root->lock);
+}
+
+/*
+ * Initialize the hot range tree. Should be called for each new inode
+ * access or other user of the hot_range interface.
+ */
+void hot_range_tree_init(struct hot_inode_item *he)
+{
+	INIT_RADIX_TREE(&he->hot_range_tree, GFP_ATOMIC);
+	spin_lock_init(&he->lock);
+}
+
+/*
+ * Initialize a new hot_range_item structure. The new structure is
+ * returned with a reference count of one and needs to be
+ * freed using free_range_item()
+ */
+static void hot_range_item_init(struct hot_range_item *hr, loff_t start,
+				struct hot_inode_item *he)
+{
+	hr->start = start;
+	hr->len = RANGE_SIZE;
+	hr->hot_inode = he;
+	kref_init(&hr->hot_range.refs);
+	spin_lock_init(&hr->hot_range.lock);
+	hr->hot_range.hot_freq_data.avg_delta_reads = (u64) -1;
+	hr->hot_range.hot_freq_data.avg_delta_writes = (u64) -1;
+	hr->hot_range.hot_freq_data.flags = FREQ_DATA_TYPE_RANGE;
+}
+
+/*
+ * Initialize a new hot_inode_item structure. The new structure is
+ * returned with a reference count of one and needs to be
+ * freed using hot_free_inode_item()
+ */
+static void hot_inode_item_init(struct hot_inode_item *he,
+				unsigned long ino,
+				struct radix_tree_root *hot_inode_tree)
+{
+	he->i_ino = ino;
+	he->hot_inode_tree = hot_inode_tree;
+	kref_init(&he->hot_inode.refs);
+	spin_lock_init(&he->hot_inode.lock);
+	he->hot_inode.hot_freq_data.avg_delta_reads = (u64) -1;
+	he->hot_inode.hot_freq_data.avg_delta_writes = (u64) -1;
+	he->hot_inode.hot_freq_data.flags = FREQ_DATA_TYPE_INODE;
+	hot_range_tree_init(he);
+}
+
+/*
+ * Initialize kmem cache for hot_inode_item and hot_range_item.
+ */
+void __init hot_cache_init(void)
+{
+	hot_inode_item_cachep = kmem_cache_create("hot_inode_item",
+			sizeof(struct hot_inode_item), 0,
+			SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD,
+			NULL);
+	if (!hot_inode_item_cachep)
+		return;
+
+	hot_range_item_cachep = kmem_cache_create("hot_range_item",
+			sizeof(struct hot_range_item), 0,
+			SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD,
+			NULL);
+	if (!hot_range_item_cachep)
+		goto err;
+
+	return;
+
+err:
+	kmem_cache_destroy(hot_inode_item_cachep);
+}
+EXPORT_SYMBOL_GPL(hot_cache_init);
diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
new file mode 100644
index 0000000..febf699
--- /dev/null
+++ b/fs/hot_tracking.h
@@ -0,0 +1,23 @@
+/*
+ * fs/hot_tracking.h
+ *
+ * Copyright (C) 2012 IBM Corp. All rights reserved.
+ * Written by Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ */
+
+#ifndef __HOT_TRACKING__
+#define __HOT_TRACKING__
+
+#include <linux/radix-tree.h>
+#include <linux/workqueue.h>
+#include <linux/hot_tracking.h>
+
+/* values for hot_freq_data flags */
+#define FREQ_DATA_TYPE_INODE (1 << 0)
+#define FREQ_DATA_TYPE_RANGE (1 << 1)
+
+#endif /* __HOT_TRACKING__ */
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
new file mode 100644
index 0000000..9273f69
--- /dev/null
+++ b/include/linux/hot_tracking.h
@@ -0,0 +1,73 @@
+/*
+ *  include/linux/hot_tracking.h
+ *
+ * This file has definitions for VFS hot data tracking
+ * structures etc.
+ *
+ * Copyright (C) 2012 IBM Corp. All rights reserved.
+ * Written by Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ */
+
+#ifndef _LINUX_HOTTRACK_H
+#define _LINUX_HOTTRACK_H
+
+#include <linux/types.h>
+#include <linux/rbtree.h>
+#include <linux/kref.h>
+#include <linux/fs.h>
+
+/*
+ * A frequency data struct holds values that are used to
+ * determine temperature of files and file ranges. These structs
+ * are members of hot_inode_item and hot_range_item
+ */
+struct hot_freq_data {
+	struct timespec last_read_time;
+	struct timespec last_write_time;
+	u32 nr_reads;
+	u32 nr_writes;
+	u64 avg_delta_reads;
+	u64 avg_delta_writes;
+	u32 flags;
+	u32 last_temp;
+};
+
+/* The common info for both following structures */
+struct hot_comm_item {
+	struct hot_freq_data hot_freq_data;  /* frequency data */
+	spinlock_t lock; /* protects object data */
+	struct kref refs;  /* prevents kfree */
+};
+
+/* An item representing an inode and its access frequency */
+struct hot_inode_item {
+	struct hot_comm_item hot_inode; /* node in hot_inode_tree */
+	struct radix_tree_root hot_range_tree; /* tree of ranges */
+	spinlock_t lock; /* protect range tree */
+	struct radix_tree_root *hot_inode_tree;
+	unsigned long i_ino; /* inode number from inode */
+};
+
+/*
+ * An item representing a range inside of
+ * an inode whose frequency is being tracked
+ */
+struct hot_range_item {
+	struct hot_comm_item hot_range;
+	struct hot_inode_item *hot_inode; /* associated hot_inode_item */
+	loff_t start; /* item offset in bytes in hot_range_tree */
+	size_t len; /* length in bytes */
+};
+
+struct hot_info {
+	struct radix_tree_root hot_inode_tree;
+	spinlock_t lock; /*protect inode tree */
+};
+
+extern void __init hot_cache_init(void);
+
+#endif  /* _LINUX_HOTTRACK_H */
-- 
1.7.6.5

[PATCH v1 hot_track 02/18] vfs: add init and cleanup functions

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Add initialization function to create some
key data structures when hot tracking is enabled;
Clean up them when hot tracking is disabled

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c            |  124 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h           |    4 ++
 include/linux/hot_tracking.h |    3 +
 3 files changed, 131 insertions(+), 0 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 806fbb0..3118c0b 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -76,12 +76,103 @@ static void hot_inode_item_init(struct hot_inode_item *he,
 	he->hot_inode_tree = hot_inode_tree;
 	kref_init(&he->hot_inode.refs);
 	spin_lock_init(&he->hot_inode.lock);
+	INIT_LIST_HEAD(&he->hot_inode.n_list);
 	he->hot_inode.hot_freq_data.avg_delta_reads = (u64) -1;
 	he->hot_inode.hot_freq_data.avg_delta_writes = (u64) -1;
 	he->hot_inode.hot_freq_data.flags = FREQ_DATA_TYPE_INODE;
 	hot_range_tree_init(he);
 }
 
+static void hot_range_item_free(struct kref *kref)
+{
+	struct hot_comm_item *comm_item = container_of(kref,
+		struct hot_comm_item, refs);
+	struct hot_range_item *hr = container_of(comm_item,
+		struct hot_range_item, hot_range);
+
+	radix_tree_delete(&hr->hot_inode->hot_range_tree, hr->start);
+	kmem_cache_free(hot_range_item_cachep, hr);
+}
+
+/*
+ * Drops the reference out on hot_range_item by one
+ * and free the structure if the reference count hits zero
+ */
+static void hot_range_item_put(struct hot_range_item *hr)
+{
+	kref_put(&hr->hot_range.refs, hot_range_item_free);
+}
+
+/* Frees the entire hot_range_tree. */
+static void hot_range_tree_free(struct hot_inode_item *he)
+{
+	struct hot_range_item *hr_nodes[8];
+	loff_t start = 0;
+	int i, n;
+
+	while (1) {
+		spin_lock(&he->lock);
+		n = radix_tree_gang_lookup(&he->hot_range_tree,
+					(void **)hr_nodes, start,
+					ARRAY_SIZE(hr_nodes));
+		if (!n) {
+			spin_unlock(&he->lock);
+			break;
+		}
+
+		start = hr_nodes[n - 1]->start + 1;
+		for (i = 0; i < n; i++)
+			hot_range_item_put(hr_nodes[i]);
+		spin_unlock(&he->lock);
+	}
+}
+
+static void hot_inode_item_free(struct kref *kref)
+{
+	struct hot_comm_item *comm_item = container_of(kref,
+			struct hot_comm_item, refs);
+	struct hot_inode_item *he = container_of(comm_item,
+			struct hot_inode_item, hot_inode);
+
+	hot_range_tree_free(he);
+	radix_tree_delete(he->hot_inode_tree, he->i_ino);
+	kmem_cache_free(hot_inode_item_cachep, he);
+}
+
+/*
+ * Drops the reference out on hot_inode_item by one
+ * and free the structure if the reference count hits zero
+ */
+void hot_inode_item_put(struct hot_inode_item *he)
+{
+	kref_put(&he->hot_inode.refs, hot_inode_item_free);
+}
+EXPORT_SYMBOL_GPL(hot_inode_item_put);
+
+/* Frees the entire hot_inode_tree. */
+static void hot_inode_tree_exit(struct hot_info *root)
+{
+	struct hot_inode_item *hi_nodes[8];
+	unsigned long ino = 0;
+	int i, n;
+
+	while (1) {
+		spin_lock(&root->lock);
+		n = radix_tree_gang_lookup(&root->hot_inode_tree,
+					   (void **)hi_nodes, ino,
+					   ARRAY_SIZE(hi_nodes));
+		if (!n) {
+			spin_unlock(&root->lock);
+			break;
+		}
+
+		ino = hi_nodes[n - 1]->i_ino + 1;
+		for (i = 0; i < n; i++)
+			hot_inode_item_put(hi_nodes[i]);
+		spin_unlock(&root->lock);
+	}
+}
+
 /*
  * Initialize kmem cache for hot_inode_item and hot_range_item.
  */
@@ -107,3 +198,36 @@ err:
 	kmem_cache_destroy(hot_inode_item_cachep);
 }
 EXPORT_SYMBOL_GPL(hot_cache_init);
+
+/*
+ * Initialize the data structures for hot data tracking.
+ */
+int hot_track_init(struct super_block *sb)
+{
+	struct hot_info *root;
+	int ret = -ENOMEM;
+
+	root = kzalloc(sizeof(struct hot_info), GFP_NOFS);
+	if (!root) {
+		printk(KERN_ERR "%s: Failed to malloc memory for "
+				"hot_info\n", __func__);
+		return ret;
+	}
+
+	sb->s_hot_root = root;
+	hot_inode_tree_init(root);
+
+	printk(KERN_INFO "VFS: Turning on hot data tracking\n");
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(hot_track_init);
+
+void hot_track_exit(struct super_block *sb)
+{
+	struct hot_info *root = sb->s_hot_root;
+
+	hot_inode_tree_exit(root);
+	kfree(root);
+}
+EXPORT_SYMBOL_GPL(hot_track_exit);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b33cfc9..c541ae7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -27,6 +27,7 @@
 #include <linux/lockdep.h>
 #include <linux/percpu-rwsem.h>
 #include <linux/blk_types.h>
+#include <linux/hot_tracking.h>
 
 #include <asm/byteorder.h>
 #include <uapi/linux/fs.h>
@@ -1321,6 +1322,9 @@ struct super_block {
 
 	/* Being remounted read-only */
 	int s_readonly_remount;
+
+	/* Hot data tracking*/
+	struct hot_info *s_hot_root;
 };
 
 /* superblock cache pruning functions */
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index 9273f69..1c364f6 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -69,5 +69,8 @@ struct hot_info {
 };
 
 extern void __init hot_cache_init(void);
+extern int hot_track_init(struct super_block *sb);
+extern void hot_track_exit(struct super_block *sb);
+extern void hot_inode_item_put(struct hot_inode_item *he);
 
 #endif  /* _LINUX_HOTTRACK_H */
-- 
1.7.6.5

[PATCH v1 hot_track 03/18] vfs: add I/O frequency update function

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Add some util helpers to update access frequencies
for one file or its range.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c            |  174 ++++++++++++++++++++++++++++++++++++++++++
 fs/hot_tracking.h            |    5 +
 include/linux/hot_tracking.h |    4 +
 3 files changed, 183 insertions(+), 0 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 3118c0b..1142ef1 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -173,6 +173,131 @@ static void hot_inode_tree_exit(struct hot_info *root)
 	}
 }
 
+struct hot_inode_item
+*hot_inode_item_lookup(struct hot_info *root, unsigned long ino)
+{
+	struct hot_inode_item *he;
+	int ret;
+
+again:
+	spin_lock(&root->lock);
+	he = radix_tree_lookup(&root->hot_inode_tree, ino);
+	if (he) {
+		kref_get(&he->hot_inode.refs);
+		spin_unlock(&root->lock);
+		return he;
+	}
+	spin_unlock(&root->lock);
+
+	he = kmem_cache_zalloc(hot_inode_item_cachep, GFP_NOFS);
+	if (!he)
+		return ERR_PTR(-ENOMEM);
+
+	hot_inode_item_init(he, ino, &root->hot_inode_tree);
+
+	ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
+	if (ret) {
+		kmem_cache_free(hot_inode_item_cachep, he);
+		return ERR_PTR(ret);
+	}
+
+	spin_lock(&root->lock);
+	ret = radix_tree_insert(&root->hot_inode_tree, ino, he);
+	if (ret == -EEXIST) {
+		kmem_cache_free(hot_inode_item_cachep, he);
+		spin_unlock(&root->lock);
+		radix_tree_preload_end();
+		goto again;
+	}
+	spin_unlock(&root->lock);
+	radix_tree_preload_end();
+
+	kref_get(&he->hot_inode.refs);
+	return he;
+}
+EXPORT_SYMBOL_GPL(hot_inode_item_lookup);
+
+static struct hot_range_item
+*hot_range_item_lookup(struct hot_inode_item *he,
+			loff_t start)
+{
+	struct hot_range_item *hr;
+	int ret;
+
+again:
+	spin_lock(&he->lock);
+	hr = radix_tree_lookup(&he->hot_range_tree, start);
+	if (hr) {
+		kref_get(&hr->hot_range.refs);
+		spin_unlock(&he->lock);
+		return hr;
+	}
+	spin_unlock(&he->lock);
+
+	hr = kmem_cache_zalloc(hot_range_item_cachep, GFP_NOFS);
+	if (!hr)
+		return ERR_PTR(-ENOMEM);
+
+	hot_range_item_init(hr, start, he);
+
+	ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
+	if (ret) {
+		kmem_cache_free(hot_range_item_cachep, hr);
+		return ERR_PTR(ret);
+	}
+
+	spin_lock(&he->lock);
+	ret = radix_tree_insert(&he->hot_range_tree, start, hr);
+	if (ret == -EEXIST) {
+		kmem_cache_free(hot_range_item_cachep, hr);
+		spin_unlock(&he->lock);
+		radix_tree_preload_end();
+		goto again;
+	}
+	spin_unlock(&he->lock);
+	radix_tree_preload_end();
+
+	kref_get(&hr->hot_range.refs);
+	return hr;
+}
+
+/*
+ * This function does the actual work of updating
+ * the frequency numbers, whatever they turn out to be.
+ */
+static void hot_rw_freq_calc(struct timespec old_atime,
+		struct timespec cur_time, u64 *avg)
+{
+	struct timespec delta_ts;
+	u64 new_delta;
+
+	delta_ts = timespec_sub(cur_time, old_atime);
+	new_delta = timespec_to_ns(&delta_ts) >> FREQ_POWER;
+
+	*avg = (*avg << FREQ_POWER) - *avg + new_delta;
+	*avg = *avg >> FREQ_POWER;
+}
+
+static void hot_freq_data_update(struct hot_freq_data *freq_data, bool write)
+{
+	struct timespec cur_time = current_kernel_time();
+
+	if (write) {
+		freq_data->nr_writes += 1;
+		hot_rw_freq_calc(freq_data->last_write_time,
+				cur_time,
+				&freq_data->avg_delta_writes);
+		freq_data->last_write_time = cur_time;
+	} else {
+		freq_data->nr_reads += 1;
+		hot_rw_freq_calc(freq_data->last_read_time,
+				freq_data->last_read_time,
+				cur_time,
+				&freq_data->avg_delta_reads);
+		freq_data->last_read_time = cur_time;
+	}
+}
+
 /*
  * Initialize kmem cache for hot_inode_item and hot_range_item.
  */
@@ -200,6 +325,55 @@ err:
 EXPORT_SYMBOL_GPL(hot_cache_init);
 
 /*
+ * Main function to update access frequency from read/writepage(s) hooks
+ */
+void hot_update_freqs(struct inode *inode, loff_t start,
+			size_t len, int rw)
+{
+	struct hot_info *root = inode->i_sb->s_hot_root;
+	struct hot_inode_item *he;
+	struct hot_range_item *hr;
+	loff_t cur, end;
+
+	if (!root || (len == 0))
+		return;
+
+	he = hot_inode_item_lookup(root, inode->i_ino);
+	if (IS_ERR(he)) {
+		WARN_ON(1);
+		return;
+	}
+
+	spin_lock(&he->hot_inode.lock);
+	hot_freq_data_update(&he->hot_inode.hot_freq_data, rw);
+	spin_unlock(&he->hot_inode.lock);
+
+	/*
+	 * Align ranges on RANGE_SIZE boundary
+	 * to prevent proliferation of range structs
+	 */
+	end = (start + len + RANGE_SIZE - 1) >> RANGE_BITS;
+	for (cur = (start >> RANGE_BITS); cur < end; cur++) {
+		hr = hot_range_item_lookup(he, cur);
+		if (IS_ERR(hr)) {
+			WARN(1, "hot_range_item_lookup returns %ld\n",
+				PTR_ERR(hr));
+			hot_inode_item_put(he);
+			return;
+		}
+
+		spin_lock(&hr->hot_range.lock);
+		hot_freq_data_update(&hr->hot_range.hot_freq_data, rw);
+		spin_unlock(&hr->hot_range.lock);
+
+		hot_range_item_put(hr);
+	}
+
+	hot_inode_item_put(he);
+}
+EXPORT_SYMBOL_GPL(hot_update_freqs);
+
+/*
  * Initialize the data structures for hot data tracking.
  */
 int hot_track_init(struct super_block *sb)
diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
index febf699..7f279af 100644
--- a/fs/hot_tracking.h
+++ b/fs/hot_tracking.h
@@ -20,4 +20,9 @@
 #define FREQ_DATA_TYPE_INODE (1 << 0)
 #define FREQ_DATA_TYPE_RANGE (1 << 1)
 
+/* size of sub-file ranges */
+#define RANGE_BITS 20
+#define RANGE_SIZE (1 << RANGE_BITS)
+#define FREQ_POWER 4
+
 #endif /* __HOT_TRACKING__ */
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index 1c364f6..3797cf0 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -72,5 +72,9 @@ extern void __init hot_cache_init(void);
 extern int hot_track_init(struct super_block *sb);
 extern void hot_track_exit(struct super_block *sb);
 extern void hot_inode_item_put(struct hot_inode_item *he);
+extern void hot_update_freqs(struct inode *inode, loff_t start,
+				size_t len, int rw);
+extern struct hot_inode_item *hot_inode_item_lookup(struct hot_info *root,
+						unsigned long ino);
 
 #endif  /* _LINUX_HOTTRACK_H */
-- 
1.7.6.5

[PATCH v1 hot_track 04/18] vfs: add two map info arrays

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Adds two map arrays which contains
a lot of list and is used to efficiently
look up the data temperature of a file or its
ranges.
  In each list of map arrays, the array node
will keep track of temperature info.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c            |   60 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/hot_tracking.h |   16 +++++++++++
 2 files changed, 76 insertions(+), 0 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 1142ef1..7101b73 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -58,6 +58,7 @@ static void hot_range_item_init(struct hot_range_item *hr, loff_t start,
 	hr->hot_inode = he;
 	kref_init(&hr->hot_range.refs);
 	spin_lock_init(&hr->hot_range.lock);
+	INIT_LIST_HEAD(&hr->hot_range.n_list);
 	hr->hot_range.hot_freq_data.avg_delta_reads = (u64) -1;
 	hr->hot_range.hot_freq_data.avg_delta_writes = (u64) -1;
 	hr->hot_range.hot_freq_data.flags = FREQ_DATA_TYPE_RANGE;
@@ -89,6 +90,16 @@ static void hot_range_item_free(struct kref *kref)
 		struct hot_comm_item, refs);
 	struct hot_range_item *hr = container_of(comm_item,
 		struct hot_range_item, hot_range);
+	struct hot_info *root = container_of(
+			hr->hot_inode->hot_inode_tree,
+		struct hot_info, hot_inode_tree);
+
+	spin_lock(&hr->hot_range.lock);
+	if (!list_empty(&hr->hot_range.n_list)) {
+		list_del_init(&hr->hot_range.n_list);
+		root->hot_map_nr--;
+	}
+	spin_unlock(&hr->hot_range.lock);
 
 	radix_tree_delete(&hr->hot_inode->hot_range_tree, hr->start);
 	kmem_cache_free(hot_range_item_cachep, hr);
@@ -133,6 +144,15 @@ static void hot_inode_item_free(struct kref *kref)
 			struct hot_comm_item, refs);
 	struct hot_inode_item *he = container_of(comm_item,
 			struct hot_inode_item, hot_inode);
+	struct hot_info *root = container_of(he->hot_inode_tree,
+		struct hot_info, hot_inode_tree);
+
+	spin_lock(&he->hot_inode.lock);
+	if (!list_empty(&he->hot_inode.n_list)) {
+		list_del_init(&he->hot_inode.n_list);
+		root->hot_map_nr--;
+	}
+	spin_unlock(&he->hot_inode.lock);
 
 	hot_range_tree_free(he);
 	radix_tree_delete(he->hot_inode_tree, he->i_ino);
@@ -299,6 +319,44 @@ static void hot_freq_data_update(struct hot_freq_data *freq_data, bool write)
 }
 
 /*
+ * Initialize inode and range map info.
+ */
+static void hot_map_init(struct hot_info *root)
+{
+	int i;
+	for (i = 0; i < HEAT_MAP_SIZE; i++) {
+		INIT_LIST_HEAD(&root->heat_inode_map[i].node_list);
+		INIT_LIST_HEAD(&root->heat_range_map[i].node_list);
+		root->heat_inode_map[i].temp = i;
+		root->heat_range_map[i].temp = i;
+	}
+}
+
+static void hot_map_list_free(struct list_head *node_list,
+				struct hot_info *root)
+{
+	struct list_head *pos, *next;
+	struct hot_comm_item *node;
+
+	list_for_each_safe(pos, next, node_list) {
+		node = list_entry(pos, struct hot_comm_item, n_list);
+		list_del_init(&node->n_list);
+		root->hot_map_nr--;
+	}
+
+}
+
+/* Free inode and range map info */
+static void hot_map_exit(struct hot_info *root)
+{
+	int i;
+	for (i = 0; i < HEAT_MAP_SIZE; i++) {
+		hot_map_list_free(&root->heat_inode_map[i].node_list, root);
+		hot_map_list_free(&root->heat_range_map[i].node_list, root);
+	}
+}
+
+/*
  * Initialize kmem cache for hot_inode_item and hot_range_item.
  */
 void __init hot_cache_init(void)
@@ -390,6 +448,7 @@ int hot_track_init(struct super_block *sb)
 
 	sb->s_hot_root = root;
 	hot_inode_tree_init(root);
+	hot_map_init(root);
 
 	printk(KERN_INFO "VFS: Turning on hot data tracking\n");
 
@@ -401,6 +460,7 @@ void hot_track_exit(struct super_block *sb)
 {
 	struct hot_info *root = sb->s_hot_root;
 
+	hot_map_exit(root);
 	hot_inode_tree_exit(root);
 	kfree(root);
 }
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index 3797cf0..5227e89 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -20,6 +20,9 @@
 #include <linux/kref.h>
 #include <linux/fs.h>
 
+#define HEAT_MAP_BITS 8
+#define HEAT_MAP_SIZE (1 << HEAT_MAP_BITS)
+
 /*
  * A frequency data struct holds values that are used to
  * determine temperature of files and file ranges. These structs
@@ -36,11 +39,18 @@ struct hot_freq_data {
 	u32 last_temp;
 };
 
+/* List heads in hot map array */
+struct hot_map_head {
+	struct list_head node_list;
+	u8 temp;
+};
+
 /* The common info for both following structures */
 struct hot_comm_item {
 	struct hot_freq_data hot_freq_data;  /* frequency data */
 	spinlock_t lock; /* protects object data */
 	struct kref refs;  /* prevents kfree */
+	struct list_head n_list; /* list node index */
 };
 
 /* An item representing an inode and its access frequency */
@@ -66,6 +76,12 @@ struct hot_range_item {
 struct hot_info {
 	struct radix_tree_root hot_inode_tree;
 	spinlock_t lock; /*protect inode tree */
+
+	/* map of inode temperature */
+	struct hot_map_head heat_inode_map[HEAT_MAP_SIZE];
+	/* map of range temperature */
+	struct hot_map_head heat_range_map[HEAT_MAP_SIZE];
+	unsigned int hot_map_nr;
 };
 
 extern void __init hot_cache_init(void);
-- 
1.7.6.5

[PATCH v1 hot_track 05/18] vfs: add hooks to enable hot tracking

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Miscellaneous features that implement hot data tracking
and generally make the hot data functions a bit more friendly.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/direct-io.c      |    6 ++++++
 mm/filemap.c        |    6 ++++++
 mm/page-writeback.c |   12 ++++++++++++
 mm/readahead.c      |    7 +++++++
 4 files changed, 31 insertions(+), 0 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index f86c720..51f13f4 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -37,6 +37,7 @@
 #include <linux/uio.h>
 #include <linux/atomic.h>
 #include <linux/prefetch.h>
+#include "hot_tracking.h"
 
 /*
  * How many user pages to map in one call to get_user_pages().  This determines
@@ -1297,6 +1298,11 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	prefetch(bdev->bd_queue);
 	prefetch((char *)bdev->bd_queue + SMP_CACHE_BYTES);
 
+	/* Hot data tracking */
+	hot_update_freqs(inode, offset,
+			iov_length(iov, nr_segs),
+			rw & WRITE);
+
 	return do_blockdev_direct_IO(rw, iocb, inode, bdev, iov, offset,
 				     nr_segs, get_block, end_io,
 				     submit_io, flags);
diff --git a/mm/filemap.c b/mm/filemap.c
index 83efee7..49a1da9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -33,6 +33,7 @@
 #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
 #include <linux/memcontrol.h>
 #include <linux/cleancache.h>
+#include <linux/hot_tracking.h>
 #include "internal.h"
 
 /*
@@ -1224,6 +1225,11 @@ readpage:
 		 * PG_error will be set again if readpage fails.
 		 */
 		ClearPageError(page);
+
+		/* Hot data tracking */
+		hot_update_freqs(inode, page->index << PAGE_CACHE_SHIFT,
+				PAGE_CACHE_SIZE, 0);
+
 		/* Start the actual read. The read will unlock the page. */
 		error = mapping->a_ops->readpage(filp, page);
 
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 830893b..27db4c1 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -35,6 +35,7 @@
 #include <linux/buffer_head.h> /* __set_page_dirty_buffers */
 #include <linux/pagevec.h>
 #include <linux/timer.h>
+#include <linux/hot_tracking.h>
 #include <trace/events/writeback.h>
 
 /*
@@ -1903,13 +1904,24 @@ EXPORT_SYMBOL(generic_writepages);
 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 {
 	int ret;
+	pgoff_t start = 0;
+	size_t count = 0;
 
 	if (wbc->nr_to_write <= 0)
 		return 0;
+
+	start = mapping->writeback_index << PAGE_CACHE_SHIFT;
+	count = wbc->nr_to_write;
+
 	if (mapping->a_ops->writepages)
 		ret = mapping->a_ops->writepages(mapping, wbc);
 	else
 		ret = generic_writepages(mapping, wbc);
+
+	/* Hot data tracking */
+	hot_update_freqs(mapping->host, (loff_t)start,
+			(count - (u64)wbc->nr_to_write) * PAGE_CACHE_SIZE, 1);
+
 	return ret;
 }
 
diff --git a/mm/readahead.c b/mm/readahead.c
index 7963f23..40a0e7f 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -19,6 +19,7 @@
 #include <linux/pagemap.h>
 #include <linux/syscalls.h>
 #include <linux/file.h>
+#include <linux/hot_tracking.h>
 
 /*
  * Initialise a struct file's readahead state.  Assumes that the caller has
@@ -138,6 +139,12 @@ static int read_pages(struct address_space *mapping, struct file *filp,
 out:
 	blk_finish_plug(&plug);
 
+	/* Hot data tracking */
+	hot_update_freqs(mapping->host,
+		(list_entry(pages->prev, struct page, lru)->index)
+			<< PAGE_CACHE_SHIFT,
+		nr_pages * PAGE_CACHE_SIZE, 0);
+
 	return ret;
 }
 
-- 
1.7.6.5

[PATCH v1 hot_track 06/18] vfs: add temp calculation function

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c |   74 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 74 insertions(+), 0 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 7101b73..3fd6255 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -25,6 +25,14 @@
 static struct kmem_cache *hot_inode_item_cachep __read_mostly;
 static struct kmem_cache *hot_range_item_cachep __read_mostly;
 
+static u64 hot_raw_shift(u64 counter, u32 bits, bool dir)
+{
+	if (dir)
+		return counter << bits;
+	else
+		return counter >> bits;
+}
+
 /*
  * Initialize the inode tree. Should be called for each new inode
  * access or other user of the hot_inode interface.
@@ -319,6 +327,72 @@ static void hot_freq_data_update(struct hot_freq_data *freq_data, bool write)
 }
 
 /*
+ * hot_temp_calc() is responsible for distilling the six heat
+ * criteria down into a single temperature value for the data,
+ * which is an integer between 0 and HEAT_MAX_VALUE.
+ */
+static u32 hot_temp_calc(struct hot_freq_data *freq_data)
+{
+	u32 result = 0;
+
+	struct timespec ckt = current_kernel_time();
+	u64 cur_time = timespec_to_ns(&ckt);
+
+	u32 nrr_heat = (u32)hot_raw_shift((u64)freq_data->nr_reads,
+					NRR_MULTIPLIER_POWER, true);
+	u32 nrw_heat = (u32)hot_raw_shift((u64)freq_data->nr_writes,
+					NRW_MULTIPLIER_POWER, true);
+
+	u64 ltr_heat =
+	hot_raw_shift((cur_time - timespec_to_ns(&freq_data->last_read_time)),
+			LTR_DIVIDER_POWER, false);
+	u64 ltw_heat =
+	hot_raw_shift((cur_time - timespec_to_ns(&freq_data->last_write_time)),
+			LTW_DIVIDER_POWER, false);
+
+	u64 avr_heat =
+	hot_raw_shift((((u64) -1) - freq_data->avg_delta_reads),
+			AVR_DIVIDER_POWER, false);
+	u64 avw_heat =
+	hot_raw_shift((((u64) -1) - freq_data->avg_delta_writes),
+			AVW_DIVIDER_POWER, false);
+
+	/* ltr_heat is now guaranteed to be u32 safe */
+	if (ltr_heat >= hot_raw_shift((u64) 1, 32, true))
+		ltr_heat = 0;
+	else
+		ltr_heat = hot_raw_shift((u64) 1, 32, true) - ltr_heat;
+
+	/* ltw_heat is now guaranteed to be u32 safe */
+	if (ltw_heat >= hot_raw_shift((u64) 1, 32, true))
+		ltw_heat = 0;
+	else
+		ltw_heat = hot_raw_shift((u64) 1, 32, true) - ltw_heat;
+
+	/* avr_heat is now guaranteed to be u32 safe */
+	if (avr_heat >= hot_raw_shift((u64) 1, 32, true))
+		avr_heat = (u32) -1;
+
+	/* avw_heat is now guaranteed to be u32 safe */
+	if (avw_heat >= hot_raw_shift((u64) 1, 32, true))
+		avw_heat = (u32) -1;
+
+	nrr_heat = (u32)hot_raw_shift((u64)nrr_heat,
+		(3 - NRR_COEFF_POWER), false);
+	nrw_heat = (u32)hot_raw_shift((u64)nrw_heat,
+		(3 - NRW_COEFF_POWER), false);
+	ltr_heat = hot_raw_shift(ltr_heat, (3 - LTR_COEFF_POWER), false);
+	ltw_heat = hot_raw_shift(ltw_heat, (3 - LTW_COEFF_POWER), false);
+	avr_heat = hot_raw_shift(avr_heat, (3 - AVR_COEFF_POWER), false);
+	avw_heat = hot_raw_shift(avw_heat, (3 - AVW_COEFF_POWER), false);
+
+	result = nrr_heat + nrw_heat + (u32) ltr_heat +
+		(u32) ltw_heat + (u32) avr_heat + (u32) avw_heat;
+
+	return result;
+}
+
+/*
  * Initialize inode and range map info.
  */
 static void hot_map_init(struct hot_info *root)
-- 
1.7.6.5

[PATCH v1 hot_track 07/18] vfs: add map info update function

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c |   67 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/hot_tracking.h |   21 ++++++++++++++++
 2 files changed, 88 insertions(+), 0 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 3fd6255..4b143a4 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -393,6 +393,73 @@ static u32 hot_temp_calc(struct hot_freq_data *freq_data)
 }
 
 /*
+ * Calculate a new temperature and, if necessary,
+ * move the list_head corresponding to this inode or range
+ * to the proper list with the new temperature
+ */
+static void hot_map_update(struct hot_freq_data *freq_data,
+				struct hot_info *root)
+{
+	struct hot_map_head *buckets, *cur_bucket;
+	struct hot_comm_item *comm_item;
+	struct hot_inode_item *he;
+	struct hot_range_item *hr;
+	u32 temp = hot_temp_calc(freq_data);
+	u8 a_temp = (u8)hot_raw_shift((u64)temp, (32 - HEAT_MAP_BITS), false);
+	u8 b_temp = (u8)hot_raw_shift((u64)freq_data->last_temp,
+					(32 - HEAT_MAP_BITS), false);
+
+	comm_item = container_of(freq_data,
+			struct hot_comm_item, hot_freq_data);
+
+	if (freq_data->flags & FREQ_DATA_TYPE_INODE) {
+		he = container_of(comm_item,
+			struct hot_inode_item, hot_inode);
+		buckets = root->heat_inode_map;
+
+		if (he == NULL)
+			return;
+
+		spin_lock(&he->hot_inode.lock);
+		if (list_empty(&he->hot_inode.n_list) || (a_temp != b_temp)) {
+			if (!list_empty(&he->hot_inode.n_list)) {
+				list_del_init(&he->hot_inode.n_list);
+				root->hot_map_nr--;
+			}
+
+			cur_bucket = buckets + a_temp;
+			list_add_tail(&he->hot_inode.n_list,
+					&cur_bucket->node_list);
+			root->hot_map_nr++;
+			freq_data->last_temp = temp;
+		}
+		spin_unlock(&he->hot_inode.lock);
+	} else if (freq_data->flags & FREQ_DATA_TYPE_RANGE) {
+		hr = container_of(comm_item,
+			struct hot_range_item, hot_range);
+		buckets = root->heat_range_map;
+
+		if (hr == NULL)
+			return;
+
+		spin_lock(&hr->hot_range.lock);
+		if (list_empty(&hr->hot_range.n_list) || (a_temp != b_temp)) {
+			if (!list_empty(&hr->hot_range.n_list)) {
+				list_del_init(&hr->hot_range.n_list);
+				root->hot_map_nr--;
+			}
+
+			cur_bucket = buckets + a_temp;
+			list_add_tail(&hr->hot_range.n_list,
+					&cur_bucket->node_list);
+			root->hot_map_nr++;
+			freq_data->last_temp = temp;
+		}
+		spin_unlock(&hr->hot_range.lock);
+	}
+}
+
+/*
  * Initialize inode and range map info.
  */
 static void hot_map_init(struct hot_info *root)
diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
index 7f279af..2f209b6 100644
--- a/fs/hot_tracking.h
+++ b/fs/hot_tracking.h
@@ -25,4 +25,25 @@
 #define RANGE_SIZE (1 << RANGE_BITS)
 #define FREQ_POWER 4
 
+/* NRR/NRW heat unit = 2^X accesses */
+#define NRR_MULTIPLIER_POWER 20 /* NRR - number of reads since mount */
+#define NRR_COEFF_POWER 0
+#define NRW_MULTIPLIER_POWER 20 /* NRW - number of writes since mount */
+#define NRW_COEFF_POWER 0
+
+/* LTR/LTW heat unit = 2^X ns of age */
+#define LTR_DIVIDER_POWER 30 /* LTR - time elapsed since last read(ns) */
+#define LTR_COEFF_POWER 1
+#define LTW_DIVIDER_POWER 30 /* LTW - time elapsed since last write(ns) */
+#define LTW_COEFF_POWER 1
+
+/*
+ * AVR/AVW cold unit = 2^X ns of average delta
+ * AVR/AVW heat unit = HEAT_MAX_VALUE - cold unit
+ */
+#define AVR_DIVIDER_POWER 40 /* AVR - average delta between recent reads(ns) */
+#define AVR_COEFF_POWER 0
+#define AVW_DIVIDER_POWER 40 /* AVW - average delta between recent writes(ns) */
+#define AVW_COEFF_POWER 0
+
 #endif /* __HOT_TRACKING__ */
-- 
1.7.6.5

[PATCH v1 hot_track 08/18] vfs: add aging function

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c |   56 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/hot_tracking.h |    6 +++++
 2 files changed, 62 insertions(+), 0 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 4b143a4..e85eaa6 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -392,6 +392,24 @@ static u32 hot_temp_calc(struct hot_freq_data *freq_data)
 	return result;
 }
 
+static bool hot_is_obsolete(struct hot_freq_data *freq_data)
+{
+	int ret = 0;
+	struct timespec ckt = current_kernel_time();
+
+	u64 cur_time = timespec_to_ns(&ckt);
+	u64 last_read_ns =
+		(cur_time - timespec_to_ns(&freq_data->last_read_time));
+	u64 last_write_ns =
+		(cur_time - timespec_to_ns(&freq_data->last_write_time));
+	u64 kick_ns =  TIME_TO_KICK * NSEC_PER_SEC;
+
+	if ((last_read_ns > kick_ns) && (last_write_ns > kick_ns))
+		ret = 1;
+
+	return ret;
+}
+
 /*
  * Calculate a new temperature and, if necessary,
  * move the list_head corresponding to this inode or range
@@ -459,6 +477,44 @@ static void hot_map_update(struct hot_freq_data *freq_data,
 	}
 }
 
+/* Update temperatures for each range item for aging purposes */
+static void hot_range_update(struct hot_inode_item *he,
+					struct hot_info *root)
+{
+	struct hot_range_item *hr_nodes[8];
+	loff_t start = 0;
+	bool obsolete;
+	int i, n;
+
+	while (1) {
+		spin_lock(&he->lock);
+		n = radix_tree_gang_lookup(&he->hot_range_tree,
+				(void **)hr_nodes, start,
+				ARRAY_SIZE(hr_nodes));
+		if (!n) {
+			spin_unlock(&he->lock);
+			break;
+		}
+		spin_unlock(&he->lock);
+
+		start = hr_nodes[n - 1]->start + 1;
+		for (i = 0; i < n; i++) {
+			kref_get(&hr_nodes[i]->hot_range.refs);
+			hot_map_update(
+				&hr_nodes[i]->hot_range.hot_freq_data, root);
+
+			spin_lock(&hr_nodes[i]->hot_range.lock);
+			obsolete = hot_is_obsolete(
+					&hr_nodes[i]->hot_range.hot_freq_data);
+			spin_unlock(&hr_nodes[i]->hot_range.lock);
+
+			hot_range_item_put(hr_nodes[i]);
+			if (obsolete)
+				hot_range_item_put(hr_nodes[i]);
+		}
+	}
+}
+
 /*
  * Initialize inode and range map info.
  */
diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
index 2f209b6..0d28e6f 100644
--- a/fs/hot_tracking.h
+++ b/fs/hot_tracking.h
@@ -25,6 +25,12 @@
 #define RANGE_SIZE (1 << RANGE_BITS)
 #define FREQ_POWER 4
 
+/*
+ * time to quit keeping track of
+ * tracking data (seconds)
+ */
+#define TIME_TO_KICK 300
+
 /* NRR/NRW heat unit = 2^X accesses */
 #define NRR_MULTIPLIER_POWER 20 /* NRR - number of reads since mount */
 #define NRR_COEFF_POWER 0
-- 
1.7.6.5

[PATCH v1 hot_track 09/18] vfs: add one work queue

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Add a per-superblock workqueue and a delayed_work
to run periodic work to update map info on each superblock.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c            |   85 ++++++++++++++++++++++++++++++++++++++++++
 fs/hot_tracking.h            |    3 +
 include/linux/hot_tracking.h |    3 +
 3 files changed, 91 insertions(+), 0 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index e85eaa6..552bee0 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -15,9 +15,12 @@
 #include <linux/module.h>
 #include <linux/spinlock.h>
 #include <linux/hardirq.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
 #include <linux/fs.h>
 #include <linux/blkdev.h>
 #include <linux/types.h>
+#include <linux/list_sort.h>
 #include <linux/limits.h>
 #include "hot_tracking.h"
 
@@ -553,6 +556,67 @@ static void hot_map_exit(struct hot_info *root)
 	}
 }
 
+/* Temperature compare function*/
+static int hot_temp_cmp(void *priv, struct list_head *a,
+				struct list_head *b)
+{
+	struct hot_comm_item *ap =
+			container_of(a, struct hot_comm_item, n_list);
+	struct hot_comm_item *bp =
+			container_of(b, struct hot_comm_item, n_list);
+
+	int diff = ap->hot_freq_data.last_temp
+				- bp->hot_freq_data.last_temp;
+	if (diff > 0)
+		return -1;
+	if (diff < 0)
+		return 1;
+	return 0;
+}
+
+/*
+ * Every sync period we update temperatures for
+ * each hot inode item and hot range item for aging
+ * purposes.
+ */
+static void hot_update_worker(struct work_struct *work)
+{
+	struct hot_info *root = container_of(to_delayed_work(work),
+					struct hot_info, update_work);
+	struct hot_inode_item *hi_nodes[8];
+	unsigned long ino = 0;
+	int i, n;
+
+	while (1) {
+		n = radix_tree_gang_lookup(&root->hot_inode_tree,
+				   (void **)hi_nodes, ino,
+				   ARRAY_SIZE(hi_nodes));
+		if (!n)
+			break;
+
+		ino = hi_nodes[n - 1]->i_ino + 1;
+		for (i = 0; i < n; i++) {
+			kref_get(&hi_nodes[i]->hot_inode.refs);
+			hot_map_update(
+				&hi_nodes[i]->hot_inode.hot_freq_data, root);
+			hot_range_update(hi_nodes[i], root);
+			hot_inode_item_put(hi_nodes[i]);
+		}
+	}
+
+	/* Sort temperature map info */
+	for (i = 0; i < HEAT_MAP_SIZE; i++) {
+		list_sort(NULL, &root->heat_inode_map[i].node_list,
+			hot_temp_cmp);
+		list_sort(NULL, &root->heat_range_map[i].node_list,
+			hot_temp_cmp);
+	}
+
+	/* Instert next delayed work */
+	queue_delayed_work(root->update_wq, &root->update_work,
+		msecs_to_jiffies(HEAT_UPDATE_DELAY * MSEC_PER_SEC));
+}
+
 /*
  * Initialize kmem cache for hot_inode_item and hot_range_item.
  */
@@ -647,9 +711,28 @@ int hot_track_init(struct super_block *sb)
 	hot_inode_tree_init(root);
 	hot_map_init(root);
 
+	root->update_wq = alloc_workqueue(
+		"hot_update_wq", WQ_NON_REENTRANT, 0);
+	if (!root->update_wq) {
+		printk(KERN_ERR "%s: Failed to create "
+				"hot update workqueue\n", __func__);
+		goto failed_wq;
+	}
+
+	/* Initialize hot tracking wq and arm one delayed work */
+	INIT_DELAYED_WORK(&root->update_work, hot_update_worker);
+	queue_delayed_work(root->update_wq, &root->update_work,
+		msecs_to_jiffies(HEAT_UPDATE_DELAY * MSEC_PER_SEC));
+
 	printk(KERN_INFO "VFS: Turning on hot data tracking\n");
 
 	return 0;
+
+failed_wq:
+	hot_map_exit(root);
+	hot_inode_tree_exit(root);
+	kfree(root);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(hot_track_init);
 
@@ -657,6 +740,8 @@ void hot_track_exit(struct super_block *sb)
 {
 	struct hot_info *root = sb->s_hot_root;
 
+	cancel_delayed_work_sync(&root->update_work);
+	destroy_workqueue(root->update_wq);
 	hot_map_exit(root);
 	hot_inode_tree_exit(root);
 	kfree(root);
diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
index 0d28e6f..6dbd27a 100644
--- a/fs/hot_tracking.h
+++ b/fs/hot_tracking.h
@@ -31,6 +31,9 @@
  */
 #define TIME_TO_KICK 300
 
+/* set how often to update temperatures (seconds) */
+#define HEAT_UPDATE_DELAY 300
+
 /* NRR/NRW heat unit = 2^X accesses */
 #define NRR_MULTIPLIER_POWER 20 /* NRR - number of reads since mount */
 #define NRR_COEFF_POWER 0
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index 5227e89..af49078 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -82,6 +82,9 @@ struct hot_info {
 	/* map of range temperature */
 	struct hot_map_head heat_range_map[HEAT_MAP_SIZE];
 	unsigned int hot_map_nr;
+
+	struct workqueue_struct *update_wq;
+	struct delayed_work update_work;
 };
 
 extern void __init hot_cache_init(void);
-- 
1.7.6.5

[PATCH v1 hot_track 10/18] vfs: add FS hot type support

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Introduce one way to enable that specific FS
can inject its own hot tracking type.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c            |   43 +++++++++++++++++++++++++++++++----------
 fs/hot_tracking.h            |    1 -
 include/linux/fs.h           |    1 +
 include/linux/hot_tracking.h |   19 ++++++++++++++++++
 4 files changed, 52 insertions(+), 12 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 552bee0..06127cf 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -64,8 +64,11 @@ void hot_range_tree_init(struct hot_inode_item *he)
 static void hot_range_item_init(struct hot_range_item *hr, loff_t start,
 				struct hot_inode_item *he)
 {
+	struct hot_info *root = container_of(he->hot_inode_tree,
+				struct hot_info, hot_inode_tree);
+
 	hr->start = start;
-	hr->len = RANGE_SIZE;
+	hr->len = hot_raw_shift(1, root->hot_type->range_bits, true);
 	hr->hot_inode = he;
 	kref_init(&hr->hot_range.refs);
 	spin_lock_init(&hr->hot_range.lock);
@@ -309,19 +312,21 @@ static void hot_rw_freq_calc(struct timespec old_atime,
 	*avg = *avg >> FREQ_POWER;
 }
 
-static void hot_freq_data_update(struct hot_freq_data *freq_data, bool write)
+static void hot_freq_data_update(struct hot_info *root,
+		struct hot_freq_data *freq_data, bool write)
 {
 	struct timespec cur_time = current_kernel_time();
 
 	if (write) {
 		freq_data->nr_writes += 1;
-		hot_rw_freq_calc(freq_data->last_write_time,
+		root->hot_type->ops.hot_rw_freq_calc_fn(
+				freq_data->last_write_time,
 				cur_time,
 				&freq_data->avg_delta_writes);
 		freq_data->last_write_time = cur_time;
 	} else {
 		freq_data->nr_reads += 1;
-		hot_rw_freq_calc(freq_data->last_read_time,
+			root->hot_type->ops.hot_rw_freq_calc_fn(
 				freq_data->last_read_time,
 				cur_time,
 				&freq_data->avg_delta_reads);
@@ -425,7 +430,7 @@ static void hot_map_update(struct hot_freq_data *freq_data,
 	struct hot_comm_item *comm_item;
 	struct hot_inode_item *he;
 	struct hot_range_item *hr;
-	u32 temp = hot_temp_calc(freq_data);
+	u32 temp = root->hot_type->ops.hot_temp_calc_fn(freq_data);
 	u8 a_temp = (u8)hot_raw_shift((u64)temp, (32 - HEAT_MAP_BITS), false);
 	u8 b_temp = (u8)hot_raw_shift((u64)freq_data->last_temp,
 					(32 - HEAT_MAP_BITS), false);
@@ -507,7 +512,7 @@ static void hot_range_update(struct hot_inode_item *he,
 				&hr_nodes[i]->hot_range.hot_freq_data, root);
 
 			spin_lock(&hr_nodes[i]->hot_range.lock);
-			obsolete = hot_is_obsolete(
+			obsolete = root->hot_type->ops.hot_is_obsolete_fn(
 					&hr_nodes[i]->hot_range.hot_freq_data);
 			spin_unlock(&hr_nodes[i]->hot_range.lock);
 
@@ -652,6 +657,7 @@ void hot_update_freqs(struct inode *inode, loff_t start,
 	struct hot_info *root = inode->i_sb->s_hot_root;
 	struct hot_inode_item *he;
 	struct hot_range_item *hr;
+	u64 range_size;
 	loff_t cur, end;
 
 	if (!root || (len == 0))
@@ -664,15 +670,19 @@ void hot_update_freqs(struct inode *inode, loff_t start,
 	}
 
 	spin_lock(&he->hot_inode.lock);
-	hot_freq_data_update(&he->hot_inode.hot_freq_data, rw);
+	hot_freq_data_update(root, &he->hot_inode.hot_freq_data, rw);
 	spin_unlock(&he->hot_inode.lock);
 
 	/*
-	 * Align ranges on RANGE_SIZE boundary
+	 * Align ranges on range size boundary
 	 * to prevent proliferation of range structs
 	 */
-	end = (start + len + RANGE_SIZE - 1) >> RANGE_BITS;
-	for (cur = (start >> RANGE_BITS); cur < end; cur++) {
+	range_size  = hot_raw_shift(1,
+			root->hot_type->range_bits, true);
+	end = hot_raw_shift((start + len + range_size - 1),
+			root->hot_type->range_bits, false);
+	cur = hot_raw_shift(start, root->hot_type->range_bits, false);
+	for (; cur < end; cur++) {
 		hr = hot_range_item_lookup(he, cur);
 		if (IS_ERR(hr)) {
 			WARN(1, "hot_range_item_lookup returns %ld\n",
@@ -682,7 +692,7 @@ void hot_update_freqs(struct inode *inode, loff_t start,
 		}
 
 		spin_lock(&hr->hot_range.lock);
-		hot_freq_data_update(&hr->hot_range.hot_freq_data, rw);
+		hot_freq_data_update(root, &hr->hot_range.hot_freq_data, rw);
 		spin_unlock(&hr->hot_range.lock);
 
 		hot_range_item_put(hr);
@@ -711,6 +721,17 @@ int hot_track_init(struct super_block *sb)
 	hot_inode_tree_init(root);
 	hot_map_init(root);
 
+	/* Get hot type for specific FS */
+	root->hot_type = &sb->s_type->hot_type;
+	if (!root->hot_type->ops.hot_rw_freq_calc_fn)
+		root->hot_type->ops.hot_rw_freq_calc_fn = hot_rw_freq_calc;
+	if (!root->hot_type->ops.hot_temp_calc_fn)
+		root->hot_type->ops.hot_temp_calc_fn = hot_temp_calc;
+	if (!root->hot_type->ops.hot_is_obsolete_fn)
+		root->hot_type->ops.hot_is_obsolete_fn = hot_is_obsolete;
+	if (root->hot_type->range_bits == 0)
+		root->hot_type->range_bits = RANGE_BITS;
+
 	root->update_wq = alloc_workqueue(
 		"hot_update_wq", WQ_NON_REENTRANT, 0);
 	if (!root->update_wq) {
diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
index 6dbd27a..2914203 100644
--- a/fs/hot_tracking.h
+++ b/fs/hot_tracking.h
@@ -22,7 +22,6 @@
 
 /* size of sub-file ranges */
 #define RANGE_BITS 20
-#define RANGE_SIZE (1 << RANGE_BITS)
 #define FREQ_POWER 4
 
 /*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c541ae7..4e2607d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1821,6 +1821,7 @@ struct file_system_type {
 	struct dentry *(*mount) (struct file_system_type *, int,
 		       const char *, void *);
 	void (*kill_sb) (struct super_block *);
+	struct hot_type hot_type;
 	struct module *owner;
 	struct file_system_type * next;
 	struct hlist_head fs_supers;
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index af49078..67fc0bf 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -73,6 +73,24 @@ struct hot_range_item {
 	size_t len; /* length in bytes */
 };
 
+typedef void (hot_rw_freq_calc_fn) (struct timespec old_atime,
+			struct timespec cur_time, u64 *avg);
+typedef u32 (hot_temp_calc_fn) (struct hot_freq_data *freq_data);
+typedef bool (hot_is_obsolete_fn) (struct hot_freq_data *freq_data);
+
+struct hot_func_ops {
+	hot_rw_freq_calc_fn *hot_rw_freq_calc_fn;
+	hot_temp_calc_fn *hot_temp_calc_fn;
+	hot_is_obsolete_fn *hot_is_obsolete_fn;
+};
+
+/* identifies an hot type */
+struct hot_type {
+	u64 range_bits;
+	/* fields provided by specific FS */
+	struct hot_func_ops ops;
+};
+
 struct hot_info {
 	struct radix_tree_root hot_inode_tree;
 	spinlock_t lock; /*protect inode tree */
@@ -85,6 +103,7 @@ struct hot_info {
 
 	struct workqueue_struct *update_wq;
 	struct delayed_work update_work;
+	struct hot_type *hot_type;
 };
 
 extern void __init hot_cache_init(void);
-- 
1.7.6.5

[PATCH v1 hot_track 11/18] vfs: register one shrinker

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Register a shrinker to control the amount of
memory that is used in tracking hot regions - if we are throwing
inodes out of memory due to memory pressure, we most definitely are
going to need to reduce the amount of memory the tracking code is
using, even if it means losing useful information (i.e. the shrinker
accelerates the aging process).

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c            |   61 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/hot_tracking.h |    1 +
 2 files changed, 62 insertions(+), 0 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 06127cf..3d96512 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -648,6 +648,61 @@ err:
 }
 EXPORT_SYMBOL_GPL(hot_cache_init);
 
+static int hot_track_prune_map(struct hot_map_head *map_head,
+				bool type, int nr)
+{
+	struct hot_comm_item *node;
+	int i;
+
+	for (i = 0; i < HEAT_MAP_SIZE; i++) {
+		while (!list_empty(&(map_head + i)->node_list)) {
+			if (nr-- <= 0)
+				break;
+
+			node = list_first_entry(&(map_head + i)->node_list,
+					struct hot_comm_item, n_list);
+			if (type) {
+				struct hot_inode_item *hot_inode =
+					container_of(node,
+					struct hot_inode_item, hot_inode);
+				hot_inode_item_put(hot_inode);
+			} else {
+				struct hot_range_item *hot_range =
+					container_of(node,
+					struct hot_range_item, hot_range);
+				hot_range_item_put(hot_range);
+			}
+		}
+	}
+
+	return nr;
+}
+
+/* The shrinker callback function */
+static int hot_track_prune(struct shrinker *shrink,
+			struct shrink_control *sc)
+{
+	struct hot_info *root =
+		container_of(shrink, struct hot_info, hot_shrink);
+	int ret;
+
+	if (sc->nr_to_scan == 0)
+		return root->hot_map_nr;
+
+	if (!(sc->gfp_mask & __GFP_FS))
+		return -1;
+
+	ret = hot_track_prune_map(root->heat_range_map,
+				false, sc->nr_to_scan);
+	if (ret > 0)
+		ret = hot_track_prune_map(root->heat_inode_map,
+					true, ret);
+	if (ret > 0)
+		root->hot_map_nr -= (sc->nr_to_scan - ret);
+
+	return root->hot_map_nr;
+}
+
 /*
  * Main function to update access frequency from read/writepage(s) hooks
  */
@@ -745,6 +800,11 @@ int hot_track_init(struct super_block *sb)
 	queue_delayed_work(root->update_wq, &root->update_work,
 		msecs_to_jiffies(HEAT_UPDATE_DELAY * MSEC_PER_SEC));
 
+	/* Register a shrinker callback */
+	root->hot_shrink.shrink = hot_track_prune;
+	root->hot_shrink.seeks = DEFAULT_SEEKS;
+	register_shrinker(&root->hot_shrink);
+
 	printk(KERN_INFO "VFS: Turning on hot data tracking\n");
 
 	return 0;
@@ -761,6 +821,7 @@ void hot_track_exit(struct super_block *sb)
 {
 	struct hot_info *root = sb->s_hot_root;
 
+	unregister_shrinker(&root->hot_shrink);
 	cancel_delayed_work_sync(&root->update_work);
 	destroy_workqueue(root->update_wq);
 	hot_map_exit(root);
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index 67fc0bf..43d9b53 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -104,6 +104,7 @@ struct hot_info {
 	struct workqueue_struct *update_wq;
 	struct delayed_work update_work;
 	struct hot_type *hot_type;
+	struct shrinker hot_shrink;
 };
 
 extern void __init hot_cache_init(void);
-- 
1.7.6.5

[PATCH v1 hot_track 12/18] vfs: add one ioctl interface

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  FS_IOC_GET_HEAT_INFO: return a struct containing the various
metrics collected in hot_freq_data structs, and also return a
calculated data temperature based on those metrics. Optionally, retrieve
the temperature from the hot data hash list instead of recalculating it.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/compat_ioctl.c            |    5 +++
 fs/ioctl.c                   |   74 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/hot_tracking.h |   19 +++++++++++
 3 files changed, 98 insertions(+), 0 deletions(-)

diff --git a/fs/compat_ioctl.c b/fs/compat_ioctl.c
index 4c6285f..ad1d603 100644
--- a/fs/compat_ioctl.c
+++ b/fs/compat_ioctl.c
@@ -57,6 +57,7 @@
 #include <linux/i2c-dev.h>
 #include <linux/atalk.h>
 #include <linux/gfp.h>
+#include <linux/hot_tracking.h>
 
 #include <net/bluetooth/bluetooth.h>
 #include <net/bluetooth/hci.h>
@@ -1400,6 +1401,9 @@ COMPATIBLE_IOCTL(TIOCSTART)
 COMPATIBLE_IOCTL(TIOCSTOP)
 #endif
 
+/*Hot data tracking*/
+COMPATIBLE_IOCTL(FS_IOC_GET_HEAT_INFO)
+
 /* fat 'r' ioctls. These are handled by fat with ->compat_ioctl,
    but we don't want warnings on other file systems. So declare
    them as compatible here. */
@@ -1579,6 +1583,7 @@ asmlinkage long compat_sys_ioctl(unsigned int fd, unsigned int cmd,
 	case FIBMAP:
 	case FIGETBSZ:
 	case FIONREAD:
+	case FS_IOC_GET_HEAT_INFO:
 		if (S_ISREG(f.file->f_path.dentry->d_inode->i_mode))
 			break;
 		/*FALL THROUGH*/
diff --git a/fs/ioctl.c b/fs/ioctl.c
index 3bdad6d..79fe81f 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -15,6 +15,7 @@
 #include <linux/writeback.h>
 #include <linux/buffer_head.h>
 #include <linux/falloc.h>
+#include <linux/hot_tracking.h>
 
 #include <asm/ioctls.h>
 
@@ -537,6 +538,76 @@ static int ioctl_fsthaw(struct file *filp)
 }
 
 /*
+ * Retrieve information about access frequency for the given file. Return it in
+ * a userspace-friendly struct for btrfsctl (or another tool) to parse.
+ *
+ * The temperature that is returned can be "live" -- that is, recalculated when
+ * the ioctl is called -- or it can be returned from the hashtable, reflecting
+ * the (possibly old) value that the system will use when considering files
+ * for migration. This behavior is determined by hot_heat_info->live.
+ */
+static int ioctl_heat_info(struct file *file, void __user *argp)
+{
+	struct inode *inode = file->f_dentry->d_inode;
+	struct hot_heat_info heat_info;
+	struct hot_inode_item *he;
+	int ret = 0;
+
+	if (copy_from_user((void *)&heat_info,
+			argp,
+			sizeof(struct hot_heat_info)) != 0) {
+		ret = -EFAULT;
+		goto err;
+	}
+
+	he = hot_inode_item_lookup(inode->i_sb->s_hot_root, inode->i_ino);
+	if (!he) {
+		/* we don't have any info on this file yet */
+		ret = -ENODATA;
+		goto err;
+	}
+
+	spin_lock(&he->hot_inode.lock);
+	heat_info.avg_delta_reads =
+		(__u64) he->hot_inode.hot_freq_data.avg_delta_reads;
+	heat_info.avg_delta_writes =
+		(__u64) he->hot_inode.hot_freq_data.avg_delta_writes;
+	heat_info.last_read_time =
+	(__u64) timespec_to_ns(&he->hot_inode.hot_freq_data.last_read_time);
+	heat_info.last_write_time =
+	(__u64) timespec_to_ns(&he->hot_inode.hot_freq_data.last_write_time);
+	heat_info.num_reads =
+		(__u32) he->hot_inode.hot_freq_data.nr_reads;
+	heat_info.num_writes =
+		(__u32) he->hot_inode.hot_freq_data.nr_writes;
+
+	if (heat_info.live > 0) {
+		/*
+		 * got a request for live temperature,
+		 * call hot_hash_calc_temperature to recalculate
+		 */
+		heat_info.temp =
+		inode->i_sb->s_hot_root->hot_type->ops.hot_temp_calc_fn(
+					&he->hot_inode.hot_freq_data);
+	} else {
+		/* not live temperature, get it from the hashlist */
+		heat_info.temp = he->hot_inode.hot_freq_data.last_temp;
+	}
+	spin_unlock(&he->hot_inode.lock);
+
+	hot_inode_item_put(he);
+
+	if (copy_to_user(argp, (void *)&heat_info,
+			sizeof(struct hot_heat_info))) {
+		ret = -EFAULT;
+		goto err;
+	}
+
+err:
+	return ret;
+}
+
+/*
  * When you add any new common ioctls to the switches above and below
  * please update compat_sys_ioctl() too.
  *
@@ -591,6 +662,9 @@ int do_vfs_ioctl(struct file *filp, unsigned int fd, unsigned int cmd,
 	case FIGETBSZ:
 		return put_user(inode->i_sb->s_blocksize, argp);
 
+	case FS_IOC_GET_HEAT_INFO:
+		return ioctl_heat_info(filp, argp);
+
 	default:
 		if (S_ISREG(inode->i_mode))
 			error = file_ioctl(filp, cmd, arg);
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index 43d9b53..5c0074a 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -39,6 +39,17 @@ struct hot_freq_data {
 	u32 last_temp;
 };
 
+struct hot_heat_info {
+	__u64 avg_delta_reads;
+	__u64 avg_delta_writes;
+	__u64 last_read_time;
+	__u64 last_write_time;
+	__u32 num_reads;
+	__u32 num_writes;
+	__u32 temp;
+	__u8 live;
+};
+
 /* List heads in hot map array */
 struct hot_map_head {
 	struct list_head node_list;
@@ -107,6 +118,14 @@ struct hot_info {
 	struct shrinker hot_shrink;
 };
 
+/*
+ * Hot data tracking ioctls:
+ *
+ * HOT_INFO - retrieve info on frequency of access
+ */
+#define FS_IOC_GET_HEAT_INFO _IOR('f', 17, \
+			struct hot_heat_info)
+
 extern void __init hot_cache_init(void);
 extern int hot_track_init(struct super_block *sb);
 extern void hot_track_exit(struct super_block *sb);
-- 
1.7.6.5

[PATCH v1 hot_track 13/18] vfs: add debugfs support

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Add a /sys/kernel/debug/hot_track/<device_name>/ directory for each
volume that contains two files. The first, `inode_stats', contains the
heat information for inodes that have been brought into the hot data map
structures. The second, `range_stats', contains similar information for
subfile ranges.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c            |  484 ++++++++++++++++++++++++++++++++++++++++++
 fs/hot_tracking.h            |    5 +
 include/linux/hot_tracking.h |    1 +
 3 files changed, 490 insertions(+), 0 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 3d96512..db430e8 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -21,9 +21,12 @@
 #include <linux/blkdev.h>
 #include <linux/types.h>
 #include <linux/list_sort.h>
+#include <linux/debugfs.h>
 #include <linux/limits.h>
 #include "hot_tracking.h"
 
+static struct dentry *hot_debugfs_root;
+
 /* kmem_cache pointers for slab caches */
 static struct kmem_cache *hot_inode_item_cachep __read_mostly;
 static struct kmem_cache *hot_range_item_cachep __read_mostly;
@@ -623,6 +626,475 @@ static void hot_update_worker(struct work_struct *work)
 }
 
 /*
+ * take the inode, find ranges associated with inode
+ * and print each range data struct
+ */
+static struct hot_range_item
+*hot_range_tree_walk(struct hot_inode_item *he,
+			loff_t *pos, loff_t start, bool flag)
+{
+	struct hot_range_item *hr_nodes[8];
+	loff_t l = *pos;
+	int i, n;
+
+	/* Walk the hot_range_tree for inode */
+	while (1) {
+		spin_lock(&he->lock);
+		n = radix_tree_gang_lookup(&he->hot_range_tree,
+					   (void **)hr_nodes, start,
+					   ARRAY_SIZE(hr_nodes));
+		if (!n) {
+			spin_unlock(&he->lock);
+			break;
+		}
+		spin_unlock(&he->lock);
+
+		start = hr_nodes[n - 1]->start + 1;
+		for (i = 0; i < n; i++) {
+			if ((!flag && !l--) || (flag)) {
+				if (flag)
+					(*pos)++;
+				kref_get(&hr_nodes[i]->hot_range.refs);
+				return hr_nodes[i];
+			}
+		}
+	}
+
+	return NULL;
+}
+
+static void
+*hot_inode_tree_walk(struct seq_file *seq, loff_t *pos,
+			unsigned long ino, bool type, bool flag)
+{
+	struct hot_info *root = seq->private;
+	struct hot_inode_item *hi_nodes[8];
+	struct hot_range_item *hr;
+	loff_t l = *pos;
+	int i, n;
+
+	while (1) {
+		spin_lock(&root->lock);
+		n = radix_tree_gang_lookup(&root->hot_inode_tree,
+					(void **)hi_nodes, ino,
+					ARRAY_SIZE(hi_nodes));
+		if (!n) {
+			spin_unlock(&root->lock);
+			break;
+		}
+		spin_unlock(&root->lock);
+
+		ino = hi_nodes[n - 1]->i_ino + 1;
+		for (i = 0; i < n; i++) {
+			if (!type) {
+				hr = hot_range_tree_walk(hi_nodes[i],
+						pos, 0, flag);
+				if (hr)
+					return hr;
+			} else {
+				if ((!flag && !l--) || (flag)) {
+					if (flag)
+						(*pos)++;
+					kref_get(&hi_nodes[i]->hot_inode.refs);
+					return hi_nodes[i];
+				}
+			}
+		}
+	}
+
+	return NULL;
+}
+
+static void *hot_range_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	return hot_inode_tree_walk(seq, pos, 0, false, false);
+}
+
+static void *hot_range_seq_next(struct seq_file *seq,
+				void *v, loff_t *pos)
+{
+	struct hot_range_item *hr_next, *hr = v;
+	loff_t start = hr->start + 1;
+
+	/* Walk the hot_range_tree for inode */
+	hr_next = hot_range_tree_walk(hr->hot_inode, pos, start, true);
+	if (hr_next)
+		return hr_next;
+
+	return hot_inode_tree_walk(seq, pos,
+			hr->hot_inode->i_ino + 1, false, true);
+}
+
+static void hot_range_seq_stop(struct seq_file *seq, void *v)
+{
+	struct hot_range_item *hr = v;
+
+	if (hr)
+		hot_range_item_put(hr);
+}
+
+static int hot_range_seq_show(struct seq_file *seq, void *v)
+{
+	struct hot_range_item *hr = v;
+	struct hot_inode_item *he = hr->hot_inode;
+	struct hot_freq_data *freq_data = &hr->hot_range.hot_freq_data;
+	struct hot_info *root = container_of(he->hot_inode_tree,
+		struct hot_info, hot_inode_tree);
+	loff_t start = hr->start * hot_raw_shift(1,
+			root->hot_type->range_bits, true);
+
+	/* Always lock hot_inode_item first */
+	spin_lock(&he->hot_inode.lock);
+	spin_lock(&hr->hot_range.lock);
+	seq_printf(seq, "inode %lu, range start " \
+			"%llu (range len %llu) reads %u, writes %u, "
+			"avg read time %llu, avg write time %llu, temp %u\n",
+			he->i_ino, (unsigned long long)start,
+			(unsigned long long)hr->len,
+			freq_data->nr_reads,
+			freq_data->nr_writes,
+			freq_data->avg_delta_reads / NSEC_PER_MSEC,
+			freq_data->avg_delta_writes / NSEC_PER_MSEC,
+			(u8)hot_raw_shift((u64)freq_data->last_temp,
+					(32 - HEAT_MAP_BITS), false));
+	spin_unlock(&hr->hot_range.lock);
+	spin_unlock(&he->hot_inode.lock);
+
+	return 0;
+}
+
+static void *hot_inode_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	return hot_inode_tree_walk(seq, pos, 0, true, false);
+}
+
+static void *hot_inode_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct hot_inode_item *he = v;
+	unsigned long ino = he->i_ino + 1;
+
+	hot_inode_item_put(he);
+
+	return hot_inode_tree_walk(seq, pos, ino, true, true);
+}
+
+static void hot_inode_seq_stop(struct seq_file *seq, void *v)
+{
+	struct hot_inode_item *he = v;
+
+	if (he)
+		hot_inode_item_put(he);
+}
+
+static int hot_inode_seq_show(struct seq_file *seq, void *v)
+{
+	struct hot_inode_item *he = v;
+	struct hot_freq_data *freq_data = &he->hot_inode.hot_freq_data;
+
+	spin_lock(&he->hot_inode.lock);
+	seq_printf(seq, "inode %lu, reads %u, writes %u, " \
+		"avg read time %llu, avg write time %llu, temp %d\n",
+		he->i_ino,
+		freq_data->nr_reads,
+		freq_data->nr_writes,
+		freq_data->avg_delta_reads / NSEC_PER_MSEC,
+		freq_data->avg_delta_writes / NSEC_PER_MSEC,
+		(u8)hot_raw_shift((u64)freq_data->last_temp,
+				(32 - HEAT_MAP_BITS), false));
+	spin_unlock(&he->hot_inode.lock);
+
+	return 0;
+}
+
+static void *hot_spot_range_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	struct hot_info *root = seq->private;
+	struct hot_range_item *hr;
+	struct hot_comm_item *comm_item;
+	struct list_head *n_list;
+	int i;
+
+	for (i = HEAT_MAP_SIZE - 1; i >= 0; i--) {
+		n_list = seq_list_start(
+			&root->heat_range_map[i].node_list, *pos);
+		if (n_list) {
+			comm_item = container_of(n_list,
+				struct hot_comm_item, n_list);
+			hr = container_of(comm_item,
+				struct hot_range_item, hot_range);
+			kref_get(&hr->hot_range.refs);
+			return hr;
+		}
+	}
+
+	return NULL;
+}
+
+static void *hot_spot_range_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct hot_info *root = seq->private;
+	struct hot_range_item *hr_next, *hr = v;
+	struct hot_comm_item *comm_item;
+	struct list_head *n_list;
+	int i = (int)hot_raw_shift(hr->hot_range.hot_freq_data.last_temp,
+				(32 - HEAT_MAP_BITS), false);
+
+	n_list = seq_list_next(&hr->hot_range.n_list,
+		&root->heat_range_map[i].node_list, pos);
+	hot_range_item_put(hr);
+next:
+	if (n_list) {
+		comm_item = container_of(n_list,
+			struct hot_comm_item, n_list);
+		hr_next = container_of(comm_item,
+			struct hot_range_item, hot_range);
+		kref_get(&hr_next->hot_range.refs);
+		return hr_next;
+	} else if (--i >= 0) {
+		n_list = seq_list_next(&root->heat_range_map[i].node_list,
+				&root->heat_range_map[i].node_list, pos);
+		goto next;
+	}
+
+	return NULL;
+}
+
+static void *hot_spot_inode_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	struct hot_info *root = seq->private;
+	struct hot_inode_item *he;
+	struct hot_comm_item *comm_item;
+	struct list_head *n_list;
+	int i;
+
+	for (i = HEAT_MAP_SIZE - 1; i >= 0; i--) {
+		n_list = seq_list_start(
+			&root->heat_inode_map[i].node_list, *pos);
+		if (n_list) {
+			comm_item = container_of(n_list,
+				struct hot_comm_item, n_list);
+			he = container_of(comm_item,
+				struct hot_inode_item, hot_inode);
+			kref_get(&he->hot_inode.refs);
+			return he;
+		}
+	}
+
+	return NULL;
+}
+
+static void *hot_spot_inode_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct hot_info *root = seq->private;
+	struct hot_inode_item *he_next, *he = v;
+	struct hot_comm_item *comm_item;
+	struct list_head *n_list;
+	int i = (int)hot_raw_shift(he->hot_inode.hot_freq_data.last_temp,
+				(32 - HEAT_MAP_BITS), false);
+
+	n_list = seq_list_next(&he->hot_inode.n_list,
+			&root->heat_inode_map[i].node_list, pos);
+	hot_inode_item_put(he);
+next:
+	if (n_list) {
+		comm_item = container_of(n_list,
+			struct hot_comm_item, n_list);
+		he_next = container_of(comm_item,
+			struct hot_inode_item, hot_inode);
+		kref_get(&he_next->hot_inode.refs);
+		return he_next;
+	} else if (--i >= 0) {
+		n_list = seq_list_next(&root->heat_inode_map[i].node_list,
+				&root->heat_inode_map[i].node_list, pos);
+		goto next;
+	}
+
+	return NULL;
+}
+
+static const struct seq_operations hot_range_seq_ops = {
+	.start = hot_range_seq_start,
+	.next = hot_range_seq_next,
+	.stop = hot_range_seq_stop,
+	.show = hot_range_seq_show
+};
+
+static const struct seq_operations hot_inode_seq_ops = {
+	.start = hot_inode_seq_start,
+	.next = hot_inode_seq_next,
+	.stop = hot_inode_seq_stop,
+	.show = hot_inode_seq_show
+};
+
+static const struct seq_operations hot_spot_range_seq_ops = {
+	.start = hot_spot_range_seq_start,
+	.next = hot_spot_range_seq_next,
+	.stop = hot_range_seq_stop,
+	.show = hot_range_seq_show
+};
+
+static const struct seq_operations hot_spot_inode_seq_ops = {
+	.start = hot_spot_inode_seq_start,
+	.next = hot_spot_inode_seq_next,
+	.stop = hot_inode_seq_stop,
+	.show = hot_inode_seq_show
+};
+
+static int hot_range_seq_open(struct inode *inode, struct file *file)
+{
+	int ret = seq_open_private(file, &hot_range_seq_ops, 0);
+	if (ret == 0) {
+		struct seq_file *seq = file->private_data;
+		seq->private = inode->i_private;
+	}
+	return ret;
+}
+
+static int hot_inode_seq_open(struct inode *inode, struct file *file)
+{
+	int ret = seq_open_private(file, &hot_inode_seq_ops, 0);
+	if (ret == 0) {
+		struct seq_file *seq = file->private_data;
+		seq->private = inode->i_private;
+	}
+	return ret;
+}
+
+static int hot_spot_range_seq_open(struct inode *inode, struct file *file)
+{
+	int ret = seq_open_private(file, &hot_spot_range_seq_ops, 0);
+	if (ret == 0) {
+		struct seq_file *seq = file->private_data;
+		seq->private = inode->i_private;
+	}
+	return ret;
+}
+
+static int hot_spot_inode_seq_open(struct inode *inode, struct file *file)
+{
+	int ret = seq_open_private(file, &hot_spot_inode_seq_ops, 0);
+	if (ret == 0) {
+		struct seq_file *seq = file->private_data;
+		seq->private = inode->i_private;
+	}
+	return ret;
+}
+
+/* fops to override for printing range data */
+static const struct file_operations hot_debugfs_range_fops = {
+	.open = hot_range_seq_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release,
+};
+
+/* fops to override for printing inode data */
+static const struct file_operations hot_debugfs_inode_fops = {
+	.open = hot_inode_seq_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release,
+};
+
+/* fops to override for printing temperature data */
+static const struct file_operations hot_debugfs_spot_range_fops = {
+	.open = hot_spot_range_seq_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release,
+};
+
+static const struct file_operations hot_debugfs_spot_inode_fops = {
+	.open = hot_spot_inode_seq_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release,
+};
+
+static const struct hot_debugfs hot_debugfs[] = {
+	{
+		.name = "rt_stats_range",
+		.fops  = &hot_debugfs_range_fops,
+	},
+	{
+		.name = "rt_stats_inode",
+		.fops  = &hot_debugfs_inode_fops,
+	},
+	{
+		.name = "hot_spots_range",
+		.fops  = &hot_debugfs_spot_range_fops,
+	},
+	{
+		.name = "hot_spots_inode",
+		.fops  = &hot_debugfs_spot_inode_fops,
+	},
+};
+
+/* initialize debugfs */
+static int hot_debugfs_init(struct super_block *sb)
+{
+	static const char hot_name[] = "hot_track";
+	struct dentry *dentry;
+	int i, ret = 0;
+
+	/* Determine if hot debufs root has existed */
+	if (!hot_debugfs_root) {
+		hot_debugfs_root = debugfs_create_dir(hot_name, NULL);
+		if (IS_ERR(hot_debugfs_root)) {
+			ret = PTR_ERR(hot_debugfs_root);
+			return ret;
+		}
+	}
+
+	if (!S_ISDIR(hot_debugfs_root->d_inode->i_mode))
+		return -ENOTDIR;
+
+	/* create debugfs folder for this volume by mounted dev name */
+	sb->s_hot_root->vol_dentry =
+			debugfs_create_dir(sb->s_id, hot_debugfs_root);
+	if (IS_ERR(sb->s_hot_root->vol_dentry)) {
+		ret = PTR_ERR(sb->s_hot_root->vol_dentry);
+		goto err;
+	}
+
+	/* create debugfs hot data files */
+	for (i = 0; i < ARRAY_SIZE(hot_debugfs); i++) {
+		dentry = debugfs_create_file(hot_debugfs[i].name,
+					S_IFREG | S_IRUSR | S_IWUSR,
+					sb->s_hot_root->vol_dentry,
+					sb->s_hot_root,
+					hot_debugfs[i].fops);
+		if (IS_ERR(dentry)) {
+			ret = PTR_ERR(dentry);
+			goto err;
+		}
+	}
+
+	return 0;
+
+err:
+	debugfs_remove_recursive(sb->s_hot_root->vol_dentry);
+
+	if (list_empty(&hot_debugfs_root->d_subdirs))
+		debugfs_remove(hot_debugfs_root);
+
+	return ret;
+}
+
+/* remove dentries for debugsfs */
+static void hot_debugfs_exit(struct super_block *sb)
+{
+	/* remove all debugfs entries recursively from the volume root */
+	if (sb->s_hot_root->vol_dentry)
+		debugfs_remove_recursive(sb->s_hot_root->vol_dentry);
+	else
+		BUG();
+
+	if (list_empty(&hot_debugfs_root->d_subdirs))
+		debugfs_remove(hot_debugfs_root);
+}
+
+/*
  * Initialize kmem cache for hot_inode_item and hot_range_item.
  */
 void __init hot_cache_init(void)
@@ -805,10 +1277,21 @@ int hot_track_init(struct super_block *sb)
 	root->hot_shrink.seeks = DEFAULT_SEEKS;
 	register_shrinker(&root->hot_shrink);
 
+	ret = hot_debugfs_init(sb);
+	if (ret) {
+		printk(KERN_ERR "%s: hot_debugfs_init error: %d\n",
+				__func__, ret);
+		goto failed_debugfs;
+	}
+
 	printk(KERN_INFO "VFS: Turning on hot data tracking\n");
 
 	return 0;
 
+failed_debugfs:
+	unregister_shrinker(&root->hot_shrink);
+	cancel_delayed_work_sync(&root->update_work);
+	destroy_workqueue(root->update_wq);
 failed_wq:
 	hot_map_exit(root);
 	hot_inode_tree_exit(root);
@@ -826,6 +1309,7 @@ void hot_track_exit(struct super_block *sb)
 	destroy_workqueue(root->update_wq);
 	hot_map_exit(root);
 	hot_inode_tree_exit(root);
+	hot_debugfs_exit(sb);
 	kfree(root);
 }
 EXPORT_SYMBOL_GPL(hot_track_exit);
diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
index 2914203..1a445a6 100644
--- a/fs/hot_tracking.h
+++ b/fs/hot_tracking.h
@@ -54,4 +54,9 @@
 #define AVW_DIVIDER_POWER 40 /* AVW - average delta between recent writes(ns) */
 #define AVW_COEFF_POWER 0
 
+struct hot_debugfs {
+	const char *name;
+	const struct file_operations *fops;
+};
+
 #endif /* __HOT_TRACKING__ */
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index 5c0074a..d9a49f9 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -116,6 +116,7 @@ struct hot_info {
 	struct delayed_work update_work;
 	struct hot_type *hot_type;
 	struct shrinker hot_shrink;
+	struct dentry *vol_dentry;
 };
 
 /*
-- 
1.7.6.5

[PATCH v1 hot_track 14/18] procfs: add two hot_track proc files

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Add two proc files hot-kick-time and hot-update-delay
under the dir /proc/sys/fs/ in order to turn
TIME_TO_KICK and HEAT_UPDATE_DELAY into be tunable.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/hot_tracking.c            |   12 +++++++++---
 fs/hot_tracking.h            |    9 ---------
 include/linux/hot_tracking.h |    7 +++++++
 kernel/sysctl.c              |   14 ++++++++++++++
 4 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index db430e8..2e5bf6c 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -27,6 +27,12 @@
 
 static struct dentry *hot_debugfs_root;
 
+int sysctl_hot_kick_time __read_mostly = 300;
+EXPORT_SYMBOL_GPL(sysctl_hot_kick_time);
+
+int sysctl_hot_update_delay __read_mostly = 300;
+EXPORT_SYMBOL_GPL(sysctl_hot_update_delay);
+
 /* kmem_cache pointers for slab caches */
 static struct kmem_cache *hot_inode_item_cachep __read_mostly;
 static struct kmem_cache *hot_range_item_cachep __read_mostly;
@@ -413,7 +419,7 @@ static bool hot_is_obsolete(struct hot_freq_data *freq_data)
 		(cur_time - timespec_to_ns(&freq_data->last_read_time));
 	u64 last_write_ns =
 		(cur_time - timespec_to_ns(&freq_data->last_write_time));
-	u64 kick_ns =  TIME_TO_KICK * NSEC_PER_SEC;
+	u64 kick_ns =  sysctl_hot_kick_time * NSEC_PER_SEC;
 
 	if ((last_read_ns > kick_ns) && (last_write_ns > kick_ns))
 		ret = 1;
@@ -622,7 +628,7 @@ static void hot_update_worker(struct work_struct *work)
 
 	/* Instert next delayed work */
 	queue_delayed_work(root->update_wq, &root->update_work,
-		msecs_to_jiffies(HEAT_UPDATE_DELAY * MSEC_PER_SEC));
+		msecs_to_jiffies(sysctl_hot_update_delay * MSEC_PER_SEC));
 }
 
 /*
@@ -1270,7 +1276,7 @@ int hot_track_init(struct super_block *sb)
 	/* Initialize hot tracking wq and arm one delayed work */
 	INIT_DELAYED_WORK(&root->update_work, hot_update_worker);
 	queue_delayed_work(root->update_wq, &root->update_work,
-		msecs_to_jiffies(HEAT_UPDATE_DELAY * MSEC_PER_SEC));
+		msecs_to_jiffies(sysctl_hot_update_delay * MSEC_PER_SEC));
 
 	/* Register a shrinker callback */
 	root->hot_shrink.shrink = hot_track_prune;
diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
index 1a445a6..50c5681 100644
--- a/fs/hot_tracking.h
+++ b/fs/hot_tracking.h
@@ -24,15 +24,6 @@
 #define RANGE_BITS 20
 #define FREQ_POWER 4
 
-/*
- * time to quit keeping track of
- * tracking data (seconds)
- */
-#define TIME_TO_KICK 300
-
-/* set how often to update temperatures (seconds) */
-#define HEAT_UPDATE_DELAY 300
-
 /* NRR/NRW heat unit = 2^X accesses */
 #define NRR_MULTIPLIER_POWER 20 /* NRR - number of reads since mount */
 #define NRR_COEFF_POWER 0
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index d9a49f9..96c91e3 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -120,6 +120,13 @@ struct hot_info {
 };
 
 /*
+ * Two variables have meanings as below:
+ * 1. time to quit keeping track of tracking data (seconds)
+ * 2. set how often to update temperatures (seconds)
+ */
+extern int sysctl_hot_kick_time, sysctl_hot_update_delay;
+
+/*
  * Hot data tracking ioctls:
  *
  * HOT_INFO - retrieve info on frequency of access
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 26f65ea..37624fb 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1545,6 +1545,20 @@ static struct ctl_table fs_table[] = {
 		.proc_handler	= &pipe_proc_fn,
 		.extra1		= &pipe_min_size,
 	},
+	{
+		.procname	= "hot-kick-time",
+		.data		= &sysctl_hot_kick_time,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+	{
+		.procname	= "hot-update-delay",
+		.data		= &sysctl_hot_update_delay,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 	{ }
 };
 
-- 
1.7.6.5

[PATCH v1 hot_track 15/18] btrfs: add hot tracking support

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Introduce one new mount option '-o hot_track',
and add its parsing support.
  Its usage looks like:
   mount -o hot_track
   mount -o nouser,hot_track
   mount -o nouser,hot_track,loop
   mount -o hot_track,nouser

Reviewed-by:   David Sterba <dsterba@suse.cz>
Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 fs/btrfs/ctree.h |    1 +
 fs/btrfs/super.c |   22 +++++++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index c72ead8..4703178 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1756,6 +1756,7 @@ struct btrfs_ioctl_defrag_range_args {
 #define BTRFS_MOUNT_CHECK_INTEGRITY	(1 << 20)
 #define BTRFS_MOUNT_CHECK_INTEGRITY_INCLUDING_EXTENT_DATA (1 << 21)
 #define BTRFS_MOUNT_PANIC_ON_FATAL_ERROR	(1 << 22)
+#define BTRFS_MOUNT_HOT_TRACK		(1 << 23)
 
 #define btrfs_clear_opt(o, opt)		((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)		((o) |= BTRFS_MOUNT_##opt)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 915ac14..0bcc62b 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -41,6 +41,7 @@
 #include <linux/slab.h>
 #include <linux/cleancache.h>
 #include <linux/ratelimit.h>
+#include <linux/hot_tracking.h>
 #include "compat.h"
 #include "delayed-inode.h"
 #include "ctree.h"
@@ -299,6 +300,10 @@ static void btrfs_put_super(struct super_block *sb)
 	 * last process that kept it busy.  Or segfault in the aforementioned
 	 * process...  Whom would you report that to?
 	 */
+
+	/* Hot data tracking */
+	if (btrfs_test_opt(btrfs_sb(sb)->tree_root, HOT_TRACK))
+		hot_track_exit(sb);
 }
 
 enum {
@@ -311,7 +316,7 @@ enum {
 	Opt_enospc_debug, Opt_subvolrootid, Opt_defrag, Opt_inode_cache,
 	Opt_no_space_cache, Opt_recovery, Opt_skip_balance,
 	Opt_check_integrity, Opt_check_integrity_including_extent_data,
-	Opt_check_integrity_print_mask, Opt_fatal_errors,
+	Opt_check_integrity_print_mask, Opt_fatal_errors, Opt_hot_track,
 	Opt_err,
 };
 
@@ -352,6 +357,7 @@ static match_table_t tokens = {
 	{Opt_check_integrity_including_extent_data, "check_int_data"},
 	{Opt_check_integrity_print_mask, "check_int_print_mask=%d"},
 	{Opt_fatal_errors, "fatal_errors=%s"},
+	{Opt_hot_track, "hot_track"},
 	{Opt_err, NULL},
 };
 
@@ -614,6 +620,9 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 				goto out;
 			}
 			break;
+		case Opt_hot_track:
+			btrfs_set_opt(info->mount_opt, HOT_TRACK);
+			break;
 		case Opt_err:
 			printk(KERN_INFO "btrfs: unrecognized mount option "
 			       "'%s'\n", p);
@@ -841,11 +850,20 @@ static int btrfs_fill_super(struct super_block *sb,
 		goto fail_close;
 	}
 
+	if (btrfs_test_opt(fs_info->tree_root, HOT_TRACK)) {
+		err = hot_track_init(sb);
+		if (err)
+			goto fail_hot;
+	}
+
 	save_mount_options(sb, data);
 	cleancache_init_fs(sb);
 	sb->s_flags |= MS_ACTIVE;
 	return 0;
 
+fail_hot:
+	dput(sb->s_root);
+	sb->s_root = NULL;
 fail_close:
 	close_ctree(fs_info->tree_root);
 	return err;
@@ -941,6 +959,8 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
 		seq_puts(seq, ",skip_balance");
 	if (btrfs_test_opt(root, PANIC_ON_FATAL_ERROR))
 		seq_puts(seq, ",fatal_errors=panic");
+	if (btrfs_test_opt(root, HOT_TRACK))
+		seq_puts(seq, ",hot_track");
 	return 0;
 }
 
-- 
1.7.6.5

[PATCH v1 hot_track 16/18] xfs: add hot tracking support

[zwu.kernel]

From: Dave Chinner <dchinner@redhat.com>

  Connect up the VFS hot tracking support
so XFS filesystems can make use of it.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/xfs_mount.h |    1 +
 fs/xfs/xfs_super.c |   16 ++++++++++++++++
 2 files changed, 17 insertions(+), 0 deletions(-)

diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index deee09e..96d93c2 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -217,6 +217,7 @@ typedef struct xfs_mount {
 #define XFS_MOUNT_WSYNC		(1ULL << 0)	/* for nfs - all metadata ops
 						   must be synchronous except
 						   for space allocations */
+#define XFS_MOUNT_HOTTRACK      (1ULL << 1)     /* hot inode tracking */
 #define XFS_MOUNT_WAS_CLEAN	(1ULL << 3)
 #define XFS_MOUNT_FS_SHUTDOWN	(1ULL << 4)	/* atomic stop of all filesystem
 						   operations, typically for
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 26a09bd..48b3bed 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -61,6 +61,7 @@
 #include <linux/kthread.h>
 #include <linux/freezer.h>
 #include <linux/parser.h>
+#include <linux/hot_tracking.h>
 
 static const struct super_operations xfs_super_operations;
 static kmem_zone_t *xfs_ioend_zone;
@@ -114,6 +115,7 @@ mempool_t *xfs_ioend_pool;
 #define MNTOPT_NODELAYLOG  "nodelaylog"	/* Delayed logging disabled */
 #define MNTOPT_DISCARD	   "discard"	/* Discard unused blocks */
 #define MNTOPT_NODISCARD   "nodiscard"	/* Do not discard unused blocks */
+#define MNTOPT_HOTTRACK    "hot_track"  /* hot inode tracking */
 
 /*
  * Table driven mount option parser.
@@ -371,6 +373,8 @@ xfs_parseargs(
 			mp->m_flags |= XFS_MOUNT_DISCARD;
 		} else if (!strcmp(this_char, MNTOPT_NODISCARD)) {
 			mp->m_flags &= ~XFS_MOUNT_DISCARD;
+		} else if (!strcmp(this_char, MNTOPT_HOTTRACK)) {
+			mp->m_flags |= XFS_MOUNT_HOTTRACK;
 		} else if (!strcmp(this_char, "ihashsize")) {
 			xfs_warn(mp,
 	"ihashsize no longer used, option is deprecated.");
@@ -1005,6 +1009,9 @@ xfs_fs_put_super(
 {
 	struct xfs_mount	*mp = XFS_M(sb);
 
+	if (mp->m_flags & XFS_MOUNT_HOTTRACK)
+		hot_track_exit(sb);
+
 	xfs_filestream_unmount(mp);
 	cancel_delayed_work_sync(&mp->m_sync_work);
 	xfs_unmountfs(mp);
@@ -1407,7 +1414,16 @@ xfs_fs_fill_super(
 		goto out_unmount;
 	}
 
+	if (mp->m_flags & XFS_MOUNT_HOTTRACK) {
+		error = hot_track_init(sb);
+		if (error)
+			goto out_free_root;
+	}
+
 	return 0;
+ out_free_root:
+	dput(sb->s_root);
+	sb->s_root = NULL;
  out_syncd_stop:
 	xfs_syncd_stop(mp);
  out_filestream_unmount:
-- 
1.7.6.5

[PATCH v1 hot_track 17/18] ext4: add hot tracking support

[zwu.kernel]

From: Zheng Liu <wenqing.lz@taobao.com>

  Define a new mount option to add VFS hot
tracking support in order to use it in ext4.

CC: Zhi Yong Wu <zwu.kernel@gmail.com>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
---
 fs/ext4/ext4.h  |    3 +++
 fs/ext4/super.c |   13 ++++++++++++-
 2 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 3c20de1..f6cff1e 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1298,6 +1298,9 @@ struct ext4_sb_info {
 
 	/* Precomputed FS UUID checksum for seeding other checksums */
 	__u32 s_csum_seed;
+
+	/* Enable hot tracking or not */
+	int s_hottrack_enable;
 };
 
 static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 80928f7..ba9f376 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -864,6 +864,8 @@ static void ext4_put_super(struct super_block *sb)
 	ext4_ext_release(sb);
 	ext4_xattr_put_super(sb);
 
+	if (sbi->s_hottrack_enable)
+		hot_track_exit(sb);
 	if (!(sb->s_flags & MS_RDONLY)) {
 		EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
 		es->s_state = cpu_to_le16(sbi->s_mount_state);
@@ -1222,7 +1224,7 @@ enum {
 	Opt_inode_readahead_blks, Opt_journal_ioprio,
 	Opt_dioread_nolock, Opt_dioread_lock,
 	Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
-	Opt_max_dir_size_kb,
+	Opt_max_dir_size_kb, Opt_hottrack,
 };
 
 static const match_table_t tokens = {
@@ -1297,6 +1299,7 @@ static const match_table_t tokens = {
 	{Opt_init_itable, "init_itable"},
 	{Opt_noinit_itable, "noinit_itable"},
 	{Opt_max_dir_size_kb, "max_dir_size_kb=%u"},
+	{Opt_hottrack, "hot_track"},
 	{Opt_removed, "check=none"},	/* mount option from ext2/3 */
 	{Opt_removed, "nocheck"},	/* mount option from ext2/3 */
 	{Opt_removed, "reservation"},	/* mount option from ext2/3 */
@@ -1595,6 +1598,14 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
 			sbi->s_li_wait_mult = arg;
 		} else if (token == Opt_max_dir_size_kb) {
 			sbi->s_max_dir_size_kb = arg;
+		} else if (token == Opt_hottrack) {
+			if (hot_track_init(sb)) {
+				ext4_msg(sb, KERN_ERR,
+					"EXT4-fs: hot tracking initialization"
+					" failed");
+				return -1;
+			}
+			sbi->s_hottrack_enable = 1;
 		} else if (token == Opt_stripe) {
 			sbi->s_stripe = arg;
 		} else if (m->flags & MOPT_DATAJ) {
-- 
1.7.6.5

[PATCH v1 hot_track 18/18] vfs: add documentation

[zwu.kernel]

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Add one doc for VFS hot tracking feature

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 Documentation/filesystems/00-INDEX         |    2 +
 Documentation/filesystems/hot_tracking.txt |  263 ++++++++++++++++++++++++++++
 2 files changed, 265 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/filesystems/hot_tracking.txt

diff --git a/Documentation/filesystems/00-INDEX b/Documentation/filesystems/00-INDEX
index 8c624a1..b68bdff 100644
--- a/Documentation/filesystems/00-INDEX
+++ b/Documentation/filesystems/00-INDEX
@@ -118,3 +118,5 @@ xfs.txt
 	- info and mount options for the XFS filesystem.
 xip.txt
 	- info on execute-in-place for file mappings.
+hot_tracking.txt
+	- info on hot data tracking in VFS layer
diff --git a/Documentation/filesystems/hot_tracking.txt b/Documentation/filesystems/hot_tracking.txt
new file mode 100644
index 0000000..0adc524
--- /dev/null
+++ b/Documentation/filesystems/hot_tracking.txt
@@ -0,0 +1,263 @@
+Hot Data Tracking
+
+September, 2012		Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
+
+CONTENTS
+
+1. Introduction
+2. Motivation
+3. The Design
+4. How to Calc Frequency of Reads/Writes & Temperature
+5. Git Development Tree
+6. Usage Example
+
+
+1. Introduction
+
+  The feature adds experimental support for tracking data temperature
+information in VFS layer.  Essentially, this means maintaining some key
+stats(like number of reads/writes, last read/write time, frequency of
+reads/writes), then distilling those numbers down to a single
+"temperature" value that reflects what data is "hot," and using that
+temperature to move data to SSDs.
+
+  The long-term goal of the feature is to allow some FSs,
+e.g. Btrfs to intelligently utilize SSDs in a heterogenous volume.
+Incidentally, this project has been motivated by
+the Project Ideas page on the Btrfs wiki.
+
+  Of course, users are warned not to run this code outside of development
+environments. These patches are EXPERIMENTAL, and as such they might eat
+your data and/or memory. That said, the code should be relatively safe
+when the hottrack mount option are disabled.
+
+
+2. Motivation
+
+  The overall goal of enabling hot data relocation to SSD has been
+motivated by the Project Ideas page on the Btrfs wiki at
+<https://btrfs.wiki.kernel.org/index.php/Project_ideas>.
+It will divide into two steps. VFS provide hot data tracking function
+while specific FS will provide hot data relocation function.
+So as the first step of this goal, it is hoped that the patchset
+for hot data tracking will eventually mature into VFS.
+
+  This is essentially the traditional cache argument: SSD is fast and
+expensive; HDD is cheap but slow. ZFS, for example, can already take
+advantage of SSD caching. Btrfs should also be able to take advantage of
+hybrid storage without many broad, sweeping changes to existing code.
+
+
+3. The Design
+
+These include the following parts:
+
+    * Hooks in existing vfs functions to track data access frequency
+
+    * New radix-trees for tracking access frequency of inodes and sub-file
+ranges
+    The relationship between super_block and radix-tree is as below:
+hot_info.hot_inode_tree
+    Each FS instance can find hot tracking info s_hotinfo.
+In this hot_info, it store a lot of hot tracking info such as hot_inode_tree,
+inode and range list, etc.
+
+    * A list for indexing data by its temperature
+
+    * A debugfs interface for dumping data from the radix-trees
+
+    * A background kthread for updating inode heat info
+
+    * Mount options for enabling temperature tracking(-o hot_track,
+default mean disabled)
+    * An ioctl to retrieve the frequency information collected for a certain
+file
+    * Ioctls to enable/disable frequency tracking per inode.
+
+Let us see their relationship as below:
+
+    * hot_info.hot_inode_tree indexes hot_inode_items, one per inode
+
+    * hot_inode_item contains access frequency data for that inode
+
+    * hot_inode_item holds a heat list node to index the access
+frequency data for that inode
+
+    * hot_inode_item.hot_range_tree indexes hot_range_items for that inode
+
+    * hot_range_item contains access frequency data for that range
+
+    * hot_range_item holds a heat list node to index the access
+frequency data for that range
+
+    * hot_info.heat_inode_map indexes per-inode heat list nodes
+
+    * hot_info.heat_range_map indexes per-range heat list nodes
+
+  How about some ascii art? :) Just looking at the hot inode item case
+(the range item case is the same pattern, though), we have:
+
+heat_inode_map           hot_inode_tree
+    |                         |
+    |                         V
+    |           +-------hot_comm_item--------+
+    |           |       frequency data       |
++---+           |        list_head           |
+|               V            ^ |             V
+| ...<--hot_comm_item-->...  | |  ...<--hot_comm_item-->...
+|       frequency data       | |        frequency data
++-------->list_head----------+ +--------->list_head--->.....
+       hot_range_tree                  hot_range_tree
+                                             |
+             heat_range_map                  V
+                   |           +-------hot_comm_item--------+
+                   |           |       frequency data       |
+               +---+           |        list_head           |
+               |               V            ^ |             V
+               | ...<--hot_comm_item-->...  | |  ...<--hot_comm_item-->...
+               |       frequency data       | |        frequency data
+               +-------->list_head----------+ +--------->list_head--->.....
+
+
+4. How to Calc Frequency of Reads/Writes & Temperature
+
+1.) hot_rw_freq_calc()
+
+  This function does the actual work of updating the frequency numbers,
+whatever they turn out to be. FREQ_POWER determines how many atime
+deltas we keep track of (as a power of 2). So, setting it to anything above
+16ish is probably overkill. Also, the higher the power, the more bits get
+right shifted out of the timestamp, reducing precision, so take note of that
+as well.
+
+  The caller should have already locked freq_data's parent's spinlock.
+
+  FREQ_POWER, defined immediately below, determines how heavily to weight
+the current frequency numbers against the newest access. For example, a value
+of 4 means that the new access information will be weighted 1/16th (ie 2^-4)
+as heavily as the existing frequency info. In essence, this is a kludged-
+together version of a weighted average, since we can't afford to keep all of
+the information that it would take to get a _real_ weighted average.
+
+2.) Some Micro explaination
+
+  The following comments explain what exactly comprises a unit of heat.
+Each of six values of heat are calculated and combined in order to form an
+overall temperature for the data:
+
+    * NRR - number of reads since mount
+    * NRW - number of writes since mount
+    * LTR - time elapsed since last read (ns)
+    * LTW - time elapsed since last write (ns)
+    * AVR - average delta between recent reads (ns)
+    * AVW - average delta between recent writes (ns)
+
+  These values are divided (right-shifted) according to the *_DIVIDER_POWER
+values defined below to bring the numbers into a reasonable range. You can
+modify these values to fit your needs. However, each heat unit is a u32 and
+thus maxes out at 2^32 - 1. Therefore, you must choose your dividers quite
+carefully or else they could max out or be stuck at zero quite easily.
+(E.g., if you chose AVR_DIVIDER_POWER = 0, nothing less than 4s of atime
+delta would bring the temperature above zero, ever.)
+
+  Finally, each value is added to the overall temperature between 0 and 8
+times, depending on its *_COEFF_POWER value. Note that the coefficients are
+also actually implemented with shifts, so take care to treat these values
+as powers of 2. (I.e., 0 means we'll add it to the temp once; 1 = 2x, etc.)
+
+    * AVR/AVW cold unit = 2^X ns of average delta
+    * AVR/AVW heat unit = HEAT_MAX_VALUE - cold unit
+
+  E.g., data with an average delta between 0 and 2^X ns will have a cold
+value of 0, which means a heat value equal to HEAT_MAX_VALUE.
+
+3.) hot_temp_calc()
+
+  This function is responsible for distilling the six heat
+criteria, which are described in detail in hot_tracking.h) down into a single
+temperature value for the data, which is an integer between 0
+and HEAT_MAX_VALUE.
+
+  To accomplish this, the raw values from the hot_freq_data structure
+are shifted various ways in order to make the temperature calculation more
+or less sensitive to each value.
+
+  Once this calibration has happened, we do some additional normalization and
+make sure that everything fits nicely in a u32. From there, we take a very
+rudimentary kind of "average" of each of the values, where the *_COEFF_POWER
+values act as weights for the average.
+
+  Finally, we use the HEAT_HASH_BITS value, which determines the size of the
+heat list array, to normalize the temperature to the proper granularity.
+
+
+5. Git Development Tree
+
+  This feature is still on development and review, so if you're interested,
+you can pull from the git repository at the following location:
+
+  https://github.com/wuzhy/kernel.git hot_tracking
+  git://github.com/wuzhy/kernel.git hot_tracking
+
+
+6. Usage Example
+
+1.) To use hot tracking, you should mount like this:
+
+$ mount -o hot_track /dev/sdb /mnt
+[ 1505.894078] device label test devid 1 transid 29 /dev/sdb
+[ 1505.952977] btrfs: disk space caching is enabled
+[ 1506.069678] vfs: turning on hot data tracking
+
+2.) Mount debugfs at first:
+
+$ mount -t debugfs none /sys/kernel/debug
+$ ls -l /sys/kernel/debug/hot_track/
+total 0
+drwxr-xr-x 2 root root 0 Aug  8 04:40 sdb
+$ ls -l /sys/kernel/debug/hot_track/sdb
+total 0
+-rw-r--r-- 1 root root 0 Aug  8 04:40 rt_stats_inode
+-rw-r--r-- 1 root root 0 Aug  8 04:40 rt_stats_range
+
+3.) View information about hot tracking from debugfs:
+
+$ echo "hot tracking test" > /mnt/file
+$ cat /sys/kernel/debug/hot_track/sdb/rt_stats_inode
+inode #279, reads 0, writes 1, avg read time 18446744073709551615,
+avg write time 5251566408153596, temp 109
+$ cat /sys/kernel/debug/hot_track/sdb/range_data
+inode #279, range start 0 (range len 1048576) reads 0, writes 1,
+avg read time 18446744073709551615, avg write time 1128690176623144209, temp 64
+
+$ echo "hot data tracking test" >> /mnt/file
+$ cat /sys/kernel/debug/hot_track/sdb/rt_stats_inode
+inode #279, reads 0, writes 2, avg read time 18446744073709551615,
+avg write time 4923343766042451, temp 109
+$ cat /sys/kernel/debug/hot_track/sdb/range_data
+inode #279, range start 0 (range len 1048576) reads 0, writes 2,
+avg read time 18446744073709551615, avg write time 1058147040842596150, temp 64
+
+4.) Check temp sorting result of some nodes:
+
+$ cat /sys/kernel/debug/hot_track/loop0/hot_spots_inode
+inode #5248773, reads 0, writes 244,
+avg read time 18446744073709, avg write time 822, temp 111
+inode #878523, reads 0, writes 1,
+avg read time 18446744073709, avg write time 5278036898, temp 109
+inode #878524, reads 0, writes 1,
+avg read time 18446744073709, avg write time 5278036898, temp 109
+
+5.) Tune some hot tracking parameters as below:
+
+$ cat /proc/sys/fs/hot-kick-time
+300
+$ echo 360 > /proc/sys/fs/hot-kick-time
+$ cat /proc/sys/fs/hot-kick-time
+360
+$ cat /proc/sys/fs/hot-update-delay
+300
+$ echo 360 > /proc/sys/fs/hot-update-delay
+$ cat /proc/sys/fs/hot-update-delay
+360
+
-- 
1.7.6.5