[PATCH v6 02/11] VFS hot tracking: Track IO and record heat information

Zhi Yong Wu
2013-11-06T13:48:19Z

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

This patch adds read/write code paths: include read_pages(),
do_writepages(), do_generic_file_read() and __blockdev_direct_IO()
to record heat information.

When real disk i/o for an inode is done, its own hot_inode_item will
be created or updated in the RB tree for the filesystem, and the i/o freq for
all of its extents will also be created/updated in the RB-tree per inode.

Each of the two structures hot_inode_item and hot_range_item
contains a hot_freq_data struct with its frequency of access metrics
(number of {reads, writes}, last {read,write} time, frequency of
{reads,writes}).

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: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
fs/hot_tracking.c | 259 +++++++++++++++++++++++++++++++++++++++++++
fs/hot_tracking.h | 3 +
fs/namei.c | 4 +
include/linux/hot_tracking.h | 19 ++++
mm/filemap.c | 24 +++-
mm/readahead.c | 6 +
6 files changed, 313 insertions(+), 2 deletions(-)

diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
index 25e7858..d68c458 100644
--- a/fs/hot_tracking.c
+++ b/fs/hot_tracking.c
@@ -22,6 +22,8 @@ static void hot_range_item_init(struct hot_range_item *hr,
struct hot_inode_item *he, loff_t start)
{
kref_init(&hr->refs);
+ hr->freq.avg_delta_reads = (u64) -1;
+ hr->freq.avg_delta_writes = (u64) -1;
hr->start = start;
hr->len = 1 << RANGE_BITS;
hr->hot_inode = he;
@@ -59,6 +61,62 @@ static void hot_range_item_put(struct hot_range_item *hr)
kref_put(&hr->refs, hot_range_item_free);
}

+static struct hot_range_item
+*hot_range_item_alloc(struct hot_inode_item *he, loff_t start)
+{
+ struct rb_node **p;
+ struct rb_node *parent = NULL;
+ struct hot_range_item *hr, *hr_new = NULL;
+
+ start = start << RANGE_BITS;
+
+ /* walk tree to find insertion point */
+redo:
+ spin_lock(&he->i_lock);
+ p = &he->hot_range_tree.rb_node;
+ while (*p) {
+ parent = *p;
+ hr = rb_entry(parent, struct hot_range_item, rb_node);
+ if (start < hr->start)
+ p = &(*p)->rb_left;
+ else if (start > (hr->start + hr->len - 1))
+ p = &(*p)->rb_right;
+ else {
+ hot_range_item_get(hr);
+ if (hr_new) {
+ /*
+ * Lost the race. Somebody else inserted
+ * the item for the range. Free the
+ * newly allocated item.
+ */
+ kmem_cache_free(hot_range_item_cachep, hr_new);
+ }
+ spin_unlock(&he->i_lock);
+
+ return hr;
+ }
+ }
+
+ if (hr_new) {
+ rb_link_node(&hr_new->rb_node, parent, p);
+ rb_insert_color(&hr_new->rb_node, &he->hot_range_tree);
+ hot_range_item_get(hr_new); /* For the caller */
+ spin_unlock(&he->i_lock);
+ return hr_new;
+ }
+ spin_unlock(&he->i_lock);
+
+ hr_new = kmem_cache_zalloc(hot_range_item_cachep, GFP_NOFS);
+ if (!hr_new)
+ return ERR_PTR(-ENOMEM);
+
+ hot_range_item_init(hr_new, he, start);
+
+ cond_resched();
+
+ goto redo;
+}
+
/*
* Free the entire hot_range_tree.
*/
@@ -82,6 +140,8 @@ static void hot_inode_item_init(struct hot_inode_item *he,
struct hot_info *root, u64 ino)
{
kref_init(&he->refs);
+ he->freq.avg_delta_reads = (u64) -1;
+ he->freq.avg_delta_writes = (u64) -1;
he->ino = ino;
he->hot_root = root;
spin_lock_init(&he->i_lock);
@@ -120,6 +180,153 @@ void hot_inode_item_put(struct hot_inode_item *he)
kref_put(&he->refs, hot_inode_item_free);
}

+static struct hot_inode_item
+*hot_inode_item_alloc(struct hot_info *root, u64 ino)
+{
+ struct rb_node **p;
+ struct rb_node *parent = NULL;
+ struct hot_inode_item *he, *he_new = NULL;
+
+ /* walk tree to find insertion point */
+redo:
+ spin_lock(&root->t_lock);
+ p = &root->hot_inode_tree.rb_node;
+ while (*p) {
+ parent = *p;
+ he = rb_entry(parent, struct hot_inode_item, rb_node);
+ if (ino < he->ino)
+ p = &(*p)->rb_left;
+ else if (ino > he->ino)
+ p = &(*p)->rb_right;
+ else {
+ hot_inode_item_get(he);
+ if (he_new) {
+ /*
+ * Lost the race. Somebody else inserted
+ * the item for the inode. Free the
+ * newly allocated item.
+ */
+ kmem_cache_free(hot_inode_item_cachep, he_new);
+ }
+ spin_unlock(&root->t_lock);
+
+ return he;
+ }
+ }
+
+ if (he_new) {
+ rb_link_node(&he_new->rb_node, parent, p);
+ rb_insert_color(&he_new->rb_node, &root->hot_inode_tree);
+ hot_inode_item_get(he_new); /* For the caller */
+ spin_unlock(&root->t_lock);
+ return he_new;
+ }
+ spin_unlock(&root->t_lock);
+
+ he_new = kmem_cache_zalloc(hot_inode_item_cachep, GFP_NOFS);
+ if (!he_new)
+ return ERR_PTR(-ENOMEM);
+
+ hot_inode_item_init(he_new, root, ino);
+
+ cond_resched();
+
+ goto redo;
+}
+
+struct hot_inode_item
+*hot_inode_item_lookup(struct hot_info *root, u64 ino)
+{
+ struct rb_node **p;
+ struct rb_node *parent = NULL;
+ struct hot_inode_item *he;
+
+ /* walk tree to find insertion point */
+ spin_lock(&root->t_lock);
+ p = &root->hot_inode_tree.rb_node;
+ while (*p) {
+ parent = *p;
+ he = rb_entry(parent, struct hot_inode_item, rb_node);
+ if (ino < he->ino)
+ p = &(*p)->rb_left;
+ else if (ino > he->ino)
+ p = &(*p)->rb_right;
+ else {
+ hot_inode_item_get(he);
+ spin_unlock(&root->t_lock);
+
+ return he;
+ }
+ }
+ spin_unlock(&root->t_lock);
+
+ return ERR_PTR(-ENOENT);
+}
+
+void hot_inode_item_unlink(struct inode *inode)
+{
+ struct hot_info *root = inode->i_sb->s_hot_root;
+ struct hot_inode_item *he;
+
+ if (!(inode->i_sb->s_flags & MS_HOTTRACK)
+ || !S_ISREG(inode->i_mode))
+ return;
+
+ he = hot_inode_item_lookup(root, inode->i_ino);
+ if (IS_ERR(he))
+ return;
+
+ spin_lock(&root->t_lock);
+ hot_inode_item_put(he);
+ hot_inode_item_put(he); /* For the caller */
+ spin_unlock(&root->t_lock);
+}
+
+/*
+ * This function does the actual work of updating
+ * the frequency numbers.
+ *
+ * avg_delta_{reads,writes} are indeed a kind of simple moving
+ * average of the time difference between each of the last
+ * 2^(FREQ_POWER) reads/writes. If there have not yet been that
+ * many reads or writes, it's likely that the values will be very
+ * large; They are initialized to the largest possible value for the
+ * data type. Simply, we don't want a few fast access to a file to
+ * automatically make it appear very hot.
+ */
+static void hot_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_update(struct hot_info *root,
+ struct hot_freq *freq, bool write)
+{
+ struct timespec cur_time = current_kernel_time();
+
+ if (write) {
+ freq->nr_writes += 1;
+ hot_freq_calc(freq->last_write_time,
+ cur_time,
+ &freq->avg_delta_writes);
+ freq->last_write_time = cur_time;
+ } else {
+ freq->nr_reads += 1;
+ hot_freq_calc(freq->last_read_time,
+ cur_time,
+ &freq->avg_delta_reads);
+ freq->last_read_time = cur_time;
+ }
+}
+
/*
* Initialize kmem cache for hot_inode_item and hot_range_item.
*/
@@ -136,6 +343,58 @@ void __init hot_cache_init(void)
kmem_cache_destroy(hot_inode_item_cachep);
}

+/*
+ * Main function to update i/o access frequencies, and it will be called
+ * from read/writepages() hooks, which are read_pages(), do_writepages(),
+ * do_generic_file_read(), and __blockdev_direct_IO().
+ */
+inline void hot_freqs_update(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;
+ u64 range_size;
+ loff_t cur, end;
+
+ if (!(inode->i_sb->s_flags & MS_HOTTRACK) || (len == 0)
+ || !S_ISREG(inode->i_mode) || !inode->i_nlink)
+ return;
+
+ he = hot_inode_item_alloc(root, inode->i_ino);
+ if (IS_ERR(he))
+ return;
+
+ hot_freq_update(root, &he->freq, rw);
+
+ /*
+ * Align ranges on range size boundary
+ * to prevent proliferation of range structs
+ */
+ range_size = 1 << RANGE_BITS;
+ end = (start + len + range_size - 1) >> RANGE_BITS;
+ cur = start >> RANGE_BITS;
+ for (; cur < end; cur++) {
+ hr = hot_range_item_alloc(he, cur);
+ if (IS_ERR(hr)) {
+ WARN(1, "hot_range_item_alloc returns %ld\n",
+ PTR_ERR(hr));
+ return;
+ }
+
+ hot_freq_update(root, &hr->freq, rw);
+
+ spin_lock(&he->i_lock);
+ hot_range_item_put(hr);
+ spin_unlock(&he->i_lock);
+ }
+
+ spin_lock(&root->t_lock);
+ hot_inode_item_put(he);
+ spin_unlock(&root->t_lock);
+}
+EXPORT_SYMBOL(hot_freqs_update);
+
static struct hot_info *hot_tree_init(struct super_block *sb)
{
struct hot_info *root;
diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
index 51d829e..56ab13c 100644
--- a/fs/hot_tracking.h
+++ b/fs/hot_tracking.h
@@ -16,8 +16,11 @@

/* size of sub-file ranges */
#define RANGE_BITS 20
+#define FREQ_POWER 4

void __init hot_cache_init(void);
void hot_inode_item_put(struct hot_inode_item *he);
+struct hot_inode_item *hot_inode_item_lookup(struct hot_info *root, u64 ino);
+void hot_inode_item_unlink(struct inode *inode);

#endif /* __HOT_TRACKING__ */
diff --git a/fs/namei.c b/fs/namei.c
index caa2805..e50af1e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -38,6 +38,7 @@

#include "internal.h"
#include "mount.h"
+#include "hot_tracking.h"

/* [Feb-1997 T. Schoebel-Theuer]
* Fundamental changes in the pathname lookup mechanisms (namei)
@@ -3668,6 +3669,9 @@ int vfs_unlink(struct inode *dir, struct dentry *dentry)
dont_mount(dentry);
}
}
+
+ if (!error && !dentry->d_inode->i_nlink)
+ hot_inode_item_unlink(dentry->d_inode);
mutex_unlock(&dentry->d_inode->i_mutex);

/* We don't d_delete() NFS sillyrenamed files--they still exist. */
diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
index 91633db..5f02025 100644
--- a/include/linux/hot_tracking.h
+++ b/include/linux/hot_tracking.h
@@ -31,8 +31,24 @@ enum {
MAX_TYPES,
};

+/*
+ * 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 {
+ 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 last_temp;
+};
+
/* An item representing an inode and its access frequency */
struct hot_inode_item {
+ struct hot_freq freq; /* frequency data */
struct kref refs;
struct rb_node rb_node; /* rbtree index */
struct rcu_head rcu;
@@ -47,6 +63,7 @@ struct hot_inode_item {
* an inode whose frequency is being tracked
*/
struct hot_range_item {
+ struct hot_freq freq; /* frequency data */
struct kref refs;
struct rb_node rb_node; /* rbtree index */
struct rcu_head rcu;
@@ -62,5 +79,7 @@ struct hot_info {

extern int hot_track_init(struct super_block *sb);
extern void hot_track_exit(struct super_block *sb);
+extern void hot_freqs_update(struct inode *inode, loff_t start,
+ size_t len, int rw);

#endif /* _LINUX_HOTTRACK_H */
diff --git a/mm/filemap.c b/mm/filemap.c
index ae4846f..d70939d 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"

#define CREATE_TRACE_POINTS
@@ -1196,6 +1197,10 @@ page_ok:
mark_page_accessed(page);
prev_index = index;

+ /* Hot tracking */
+ hot_freqs_update(inode, page->index << PAGE_CACHE_SHIFT,
+ PAGE_CACHE_SIZE, 0);
+
/*
* Ok, we have the page, and it's up-to-date, so
* now we can copy it to user space...
@@ -1514,9 +1519,13 @@ static int page_cache_read(struct file *file, pgoff_t offset)
return -ENOMEM;

ret = add_to_page_cache_lru(page, mapping, offset, GFP_KERNEL);
- if (ret == 0)
+ if (ret == 0) {
+ /* Hot tracking */
+ hot_freqs_update(mapping->host,
+ page->index << PAGE_CACHE_SHIFT,
+ PAGE_CACHE_SIZE, 0);
ret = mapping->a_ops->readpage(file, page);
- else if (ret == -EEXIST)
+ } else if (ret == -EEXIST)
ret = 0; /* losing race to add is OK */

page_cache_release(page);
@@ -1711,6 +1720,11 @@ page_not_uptodate:
* and we need to check for errors.
*/
ClearPageError(page);
+
+ /* Hot tracking */
+ hot_freqs_update(inode, page->index << PAGE_CACHE_SHIFT,
+ PAGE_CACHE_SIZE, 0);
+
error = mapping->a_ops->readpage(file, page);
if (!error) {
wait_on_page_locked(page);
@@ -2249,6 +2263,9 @@ generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
}

if (written > 0) {
+ /* Hot tracking */
+ hot_freqs_update(inode, pos, written, 1);
+
pos += written;
if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
i_size_write(inode, pos);
@@ -2404,6 +2421,9 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
status = generic_perform_write(file, &i, pos);

if (likely(status >= 0)) {
+ /* Hot tracking */
+ hot_freqs_update(file_inode(file), pos, status, 1);
+
written += status;
*ppos = pos + status;
}
diff --git a/mm/readahead.c b/mm/readahead.c
index e4ed041..51f0e88 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
@@ -115,6 +116,11 @@ static int read_pages(struct address_space *mapping, struct file *filp,
unsigned page_idx;
int ret;

+ /* Hot tracking */
+ hot_freqs_update(mapping->host,
+ list_to_page(pages)->index << PAGE_CACHE_SHIFT,
+ (size_t)nr_pages * PAGE_CACHE_SIZE, 0);
+
blk_start_plug(&plug);

if (mapping->a_ops->readpages) {
--
1.7.11.7