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Subject[PATCH 04/18] fs: Implement lazy LRU updates for inodes.
Date
From: Nick Piggin <npiggin@suse.de>

Convert the inode LRU to use lazy updates to reduce lock and
cacheline traffic. We avoid moving inodes around in the LRU list
during iget/iput operations so these frequent operations don't need
to access the LRUs. Instead, we defer the refcount checks to
reclaim-time and use a per-inode state flag, I_REFERENCED, to tell
reclaim that iget has touched the inode in the past. This means that
only reclaim should be touching the LRU with any frequency, hence
significantly reducing lock acquisitions and the amount contention
on LRU updates.

This also removes the inode_in_use list, which means we now only
have one list for tracking the inode LRU status. This makes it much
simpler to split out the LRU list operations under it's own lock.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/fs-writeback.c | 9 +------
fs/inode.c | 56 +++++++++++++++++++++++++++++----------------
include/linux/fs.h | 13 +++++-----
include/linux/writeback.h | 1 -
4 files changed, 44 insertions(+), 35 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 3209aff..2a61300 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -408,15 +408,8 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
* completion.
*/
redirty_tail(inode);
- } else if (atomic_read(&inode->i_count)) {
- /*
- * The inode is clean, inuse
- */
- list_move(&inode->i_list, &inode_in_use);
} else {
- /*
- * The inode is clean, unused
- */
+ /* The inode is clean */
list_move(&inode->i_list, &inode_unused);
}
}
diff --git a/fs/inode.c b/fs/inode.c
index 22ef3f1..e76d398 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -72,7 +72,6 @@ static unsigned int i_hash_shift __read_mostly;
* allowing for low-overhead inode sync() operations.
*/

-LIST_HEAD(inode_in_use);
LIST_HEAD(inode_unused);
static struct hlist_head *inode_hashtable __read_mostly;

@@ -291,6 +290,7 @@ void inode_init_once(struct inode *inode)
INIT_HLIST_NODE(&inode->i_hash);
INIT_LIST_HEAD(&inode->i_dentry);
INIT_LIST_HEAD(&inode->i_devices);
+ INIT_LIST_HEAD(&inode->i_list);
INIT_RADIX_TREE(&inode->i_data.page_tree, GFP_ATOMIC);
spin_lock_init(&inode->i_data.tree_lock);
spin_lock_init(&inode->i_data.i_mmap_lock);
@@ -317,12 +317,7 @@ static void init_once(void *foo)
*/
void __iget(struct inode *inode)
{
- if (atomic_inc_return(&inode->i_count) != 1)
- return;
-
- if (!(inode->i_state & (I_DIRTY|I_SYNC)))
- list_move(&inode->i_list, &inode_in_use);
- percpu_counter_dec(&nr_inodes_unused);
+ atomic_inc(&inode->i_count);
}

void end_writeback(struct inode *inode)
@@ -367,7 +362,7 @@ static void dispose_list(struct list_head *head)
struct inode *inode;

inode = list_first_entry(head, struct inode, i_list);
- list_del(&inode->i_list);
+ list_del_init(&inode->i_list);

evict(inode);

@@ -489,8 +484,15 @@ static void prune_icache(int nr_to_scan)

inode = list_entry(inode_unused.prev, struct inode, i_list);

- if (inode->i_state || atomic_read(&inode->i_count)) {
+ if (atomic_read(&inode->i_count) ||
+ (inode->i_state & ~I_REFERENCED)) {
+ list_del_init(&inode->i_list);
+ percpu_counter_dec(&nr_inodes_unused);
+ continue;
+ }
+ if (inode->i_state & I_REFERENCED) {
list_move(&inode->i_list, &inode_unused);
+ inode->i_state &= ~I_REFERENCED;
continue;
}
if (inode_has_buffers(inode) || inode->i_data.nrpages) {
@@ -502,11 +504,15 @@ static void prune_icache(int nr_to_scan)
iput(inode);
spin_lock(&inode_lock);

- if (inode != list_entry(inode_unused.next,
- struct inode, i_list))
- continue; /* wrong inode or list_empty */
- if (!can_unuse(inode))
+ /*
+ * if we can't reclaim this inod immediately, give it
+ * another pass through the free list so we don't spin
+ * on it.
+ */
+ if (!can_unuse(inode)) {
+ list_move(&inode->i_list, &inode_unused);
continue;
+ }
}
list_move(&inode->i_list, &freeable);
WARN_ON(inode->i_state & I_NEW);
@@ -621,7 +627,6 @@ static inline void
__inode_add_to_lists(struct super_block *sb, struct hlist_head *head,
struct inode *inode)
{
- list_add(&inode->i_list, &inode_in_use);
list_add(&inode->i_sb_list, &sb->s_inodes);
if (head)
hlist_add_head(&inode->i_hash, head);
@@ -1238,10 +1243,12 @@ static void iput_final(struct inode *inode)
drop = generic_drop_inode(inode);

if (!drop) {
- if (!(inode->i_state & (I_DIRTY|I_SYNC)))
- list_move(&inode->i_list, &inode_unused);
- percpu_counter_inc(&nr_inodes_unused);
if (sb->s_flags & MS_ACTIVE) {
+ inode->i_state |= I_REFERENCED;
+ if (!(inode->i_state & (I_DIRTY|I_SYNC))) {
+ list_move(inode->i_list, &inode_unused);
+ percpu_counter_inc(&nr_inodes_unused);
+ }
spin_unlock(&inode_lock);
return;
}
@@ -1252,13 +1259,22 @@ static void iput_final(struct inode *inode)
spin_lock(&inode_lock);
WARN_ON(inode->i_state & I_NEW);
inode->i_state &= ~I_WILL_FREE;
- percpu_counter_dec(&nr_inodes_unused);
hlist_del_init(&inode->i_hash);
}
- list_del_init(&inode->i_list);
- list_del_init(&inode->i_sb_list);
WARN_ON(inode->i_state & I_NEW);
inode->i_state |= I_FREEING;
+
+ /*
+ * We avoid moving dirty inodes back onto the LRU now because I_FREEING
+ * is set and hence writeback_single_inode() won't move the inode
+ * around.
+ */
+ if (!list_empty(&inode->i_list)) {
+ list_del_init(&inode->i_list);
+ percpu_counter_dec(&nr_inodes_unused);
+ }
+
+ list_del_init(&inode->i_sb_list);
spin_unlock(&inode_lock);
evict(inode);
spin_lock(&inode_lock);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6f0b07f..8ff7b6b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1632,16 +1632,17 @@ struct super_operations {
*
* Q: What is the difference between I_WILL_FREE and I_FREEING?
*/
-#define I_DIRTY_SYNC 1
-#define I_DIRTY_DATASYNC 2
-#define I_DIRTY_PAGES 4
+#define I_DIRTY_SYNC 0x01
+#define I_DIRTY_DATASYNC 0x02
+#define I_DIRTY_PAGES 0x04
#define __I_NEW 3
#define I_NEW (1 << __I_NEW)
-#define I_WILL_FREE 16
-#define I_FREEING 32
-#define I_CLEAR 64
+#define I_WILL_FREE 0x10
+#define I_FREEING 0x20
+#define I_CLEAR 0x40
#define __I_SYNC 7
#define I_SYNC (1 << __I_SYNC)
+#define I_REFERENCED 0x100

#define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 72a5d64..f956b66 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -10,7 +10,6 @@
struct backing_dev_info;

extern spinlock_t inode_lock;
-extern struct list_head inode_in_use;
extern struct list_head inode_unused;

/*
--
1.7.1


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