[PATCH 6/8] fs: move i_wb_list out from under inode_lock

From: Dave Chinner
Date: Tue Mar 22 2011 - 07:24:52 EST

From: Dave Chinner <dchinner@xxxxxxxxxx>

Protect the inode writeback list with a new global lock
inode_wb_list_lock and use it to protect the list manipulations and
traversals. This lock replaces the inode_lock as the inodes on the
list can be validity checked while holding the inode->i_lock and
hence the inode_lock is no longer needed to protect the list.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
fs/block_dev.c | 4 +-
fs/fs-writeback.c | 76 ++++++++++++++++++++++++++-------------------
fs/inode.c | 12 +++++--
fs/internal.h | 5 +++
include/linux/writeback.h | 1 +
mm/backing-dev.c | 8 ++--
mm/filemap.c | 8 ++--
mm/rmap.c | 4 +-
8 files changed, 70 insertions(+), 48 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index bc39b18..2bbc0e6 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -55,13 +55,13 @@ EXPORT_SYMBOL(I_BDEV);
static void bdev_inode_switch_bdi(struct inode *inode,
struct backing_dev_info *dst)
{
- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
spin_lock(&inode->i_lock);
inode->i_data.backing_dev_info = dst;
if (inode->i_state & I_DIRTY)
list_move(&inode->i_wb_list, &dst->wb.b_dirty);
spin_unlock(&inode->i_lock);
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);
}

static sector_t max_block(struct block_device *bdev)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 5de56a2..ed80065 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -176,6 +176,17 @@ void bdi_start_background_writeback(struct backing_dev_info *bdi)
}

/*
+ * Remove the inode from the writeback list it is on.
+ */
+void inode_wb_list_del(struct inode *inode)
+{
+ spin_lock(&inode_wb_list_lock);
+ list_del_init(&inode->i_wb_list);
+ spin_unlock(&inode_wb_list_lock);
+}
+
+
+/*
* Redirty an inode: set its when-it-was dirtied timestamp and move it to the
* furthest end of its superblock's dirty-inode list.
*
@@ -188,6 +199,7 @@ static void redirty_tail(struct inode *inode)
{
struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;

+ assert_spin_locked(&inode_wb_list_lock);
if (!list_empty(&wb->b_dirty)) {
struct inode *tail;

@@ -205,14 +217,17 @@ static void requeue_io(struct inode *inode)
{
struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;

+ assert_spin_locked(&inode_wb_list_lock);
list_move(&inode->i_wb_list, &wb->b_more_io);
}

static void inode_sync_complete(struct inode *inode)
{
/*
- * Prevent speculative execution through spin_unlock(&inode_lock);
+ * Prevent speculative execution through
+ * spin_unlock(&inode_wb_list_lock);
*/
+
smp_mb();
wake_up_bit(&inode->i_state, __I_SYNC);
}
@@ -286,6 +301,7 @@ static void move_expired_inodes(struct list_head *delaying_queue,
*/
static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
{
+ assert_spin_locked(&inode_wb_list_lock);
list_splice_init(&wb->b_more_io, &wb->b_io);
move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
}
@@ -308,25 +324,23 @@ static void inode_wait_for_writeback(struct inode *inode)
wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
while (inode->i_state & I_SYNC) {
spin_unlock(&inode->i_lock);
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);
__wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
spin_lock(&inode->i_lock);
}
}

/*
- * Write out an inode's dirty pages. Called under inode_lock. Either the
- * caller has ref on the inode (either via __iget or via syscall against an fd)
- * or the inode has I_WILL_FREE set (via generic_forget_inode)
+ * Write out an inode's dirty pages. Called under inode_wb_list_lock. Either
+ * the caller has an active reference on the inode or the inode has I_WILL_FREE
+ * set.
*
* If `wait' is set, wait on the writeout.
*
* The whole writeout design is quite complex and fragile. We want to avoid
* starvation of particular inodes when others are being redirtied, prevent
* livelocks, etc.
- *
- * Called under inode_lock.
*/
static int
writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
@@ -368,7 +382,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
inode->i_state |= I_SYNC;
inode->i_state &= ~I_DIRTY_PAGES;
spin_unlock(&inode->i_lock);
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);

ret = do_writepages(mapping, wbc);

@@ -388,12 +402,10 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
* due to delalloc, clear dirty metadata flags right before
* write_inode()
*/
- spin_lock(&inode_lock);
spin_lock(&inode->i_lock);
dirty = inode->i_state & I_DIRTY;
inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
spin_unlock(&inode->i_lock);
- spin_unlock(&inode_lock);
/* Don't write the inode if only I_DIRTY_PAGES was set */
if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
int err = write_inode(inode, wbc);
@@ -401,7 +413,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
ret = err;
}

- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
spin_lock(&inode->i_lock);
inode->i_state &= ~I_SYNC;
if (!(inode->i_state & I_FREEING)) {
@@ -543,10 +555,10 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
*/
redirty_tail(inode);
}
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);
iput(inode);
cond_resched();
- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
if (wbc->nr_to_write <= 0) {
wbc->more_io = 1;
return 1;
@@ -565,7 +577,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,

if (!wbc->wb_start)
wbc->wb_start = jiffies; /* livelock avoidance */
- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
if (!wbc->for_kupdate || list_empty(&wb->b_io))
queue_io(wb, wbc->older_than_this);

@@ -583,7 +595,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
if (ret)
break;
}
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);
/* Leave any unwritten inodes on b_io */
}

@@ -592,11 +604,11 @@ static void __writeback_inodes_sb(struct super_block *sb,
{
WARN_ON(!rwsem_is_locked(&sb->s_umount));

- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
if (!wbc->for_kupdate || list_empty(&wb->b_io))
queue_io(wb, wbc->older_than_this);
writeback_sb_inodes(sb, wb, wbc, true);
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);
}

/*
@@ -735,7 +747,7 @@ static long wb_writeback(struct bdi_writeback *wb,
* become available for writeback. Otherwise
* we'll just busyloop.
*/
- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
if (!list_empty(&wb->b_more_io)) {
inode = wb_inode(wb->b_more_io.prev);
trace_wbc_writeback_wait(&wbc, wb->bdi);
@@ -743,7 +755,7 @@ static long wb_writeback(struct bdi_writeback *wb,
inode_wait_for_writeback(inode);
spin_unlock(&inode->i_lock);
}
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);
}

return wrote;
@@ -1009,7 +1021,6 @@ void __mark_inode_dirty(struct inode *inode, int flags)
{
struct super_block *sb = inode->i_sb;
struct backing_dev_info *bdi = NULL;
- bool wakeup_bdi = false;

/*
* Don't do this for I_DIRTY_PAGES - that doesn't actually
@@ -1033,7 +1044,6 @@ void __mark_inode_dirty(struct inode *inode, int flags)
if (unlikely(block_dump))
block_dump___mark_inode_dirty(inode);

- spin_lock(&inode_lock);
spin_lock(&inode->i_lock);
if ((inode->i_state & flags) != flags) {
const int was_dirty = inode->i_state & I_DIRTY;
@@ -1059,12 +1069,12 @@ void __mark_inode_dirty(struct inode *inode, int flags)
if (inode->i_state & I_FREEING)
goto out_unlock_inode;

- spin_unlock(&inode->i_lock);
/*
* If the inode was already on b_dirty/b_io/b_more_io, don't
* reposition it (that would break b_dirty time-ordering).
*/
if (!was_dirty) {
+ bool wakeup_bdi = false;
bdi = inode_to_bdi(inode);

if (bdi_cap_writeback_dirty(bdi)) {
@@ -1081,18 +1091,20 @@ void __mark_inode_dirty(struct inode *inode, int flags)
wakeup_bdi = true;
}

+ spin_unlock(&inode->i_lock);
+ spin_lock(&inode_wb_list_lock);
inode->dirtied_when = jiffies;
list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
+ spin_unlock(&inode_wb_list_lock);
+
+ if (wakeup_bdi)
+ bdi_wakeup_thread_delayed(bdi);
+ return;
}
- goto out;
}
out_unlock_inode:
spin_unlock(&inode->i_lock);
-out:
- spin_unlock(&inode_lock);

- if (wakeup_bdi)
- bdi_wakeup_thread_delayed(bdi);
}
EXPORT_SYMBOL(__mark_inode_dirty);

@@ -1296,9 +1308,9 @@ int write_inode_now(struct inode *inode, int sync)
wbc.nr_to_write = 0;

might_sleep();
- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
ret = writeback_single_inode(inode, &wbc);
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);
if (sync)
inode_sync_wait(inode);
return ret;
@@ -1320,9 +1332,9 @@ int sync_inode(struct inode *inode, struct writeback_control *wbc)
{
int ret;

- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
ret = writeback_single_inode(inode, wbc);
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);
return ret;
}
EXPORT_SYMBOL(sync_inode);
diff --git a/fs/inode.c b/fs/inode.c
index 5483d38..5a7f8ef 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -25,6 +25,7 @@
#include <linux/async.h>
#include <linux/posix_acl.h>
#include <linux/ima.h>
+#include "internal.h"

/*
* inode locking rules.
@@ -35,6 +36,8 @@
* inode_lru, inode->i_lru
* inode_sb_list_lock protects:
* sb->s_inodes, inode->i_sb_list
+ * inode_wb_list_lock protects:
+ * bdi->wb.b_{dirty,io,more_io}, inode->i_wb_list
*
* Lock ordering:
* inode_lock
@@ -43,6 +46,9 @@
* inode_sb_list_lock
* inode->i_lock
* inode_lru_lock
+ *
+ * inode_wb_list_lock
+ * inode->i_lock
*/

/*
@@ -104,6 +110,7 @@ static struct hlist_head *inode_hashtable __read_mostly;
DEFINE_SPINLOCK(inode_lock);

__cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_sb_list_lock);
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_wb_list_lock);

/*
* iprune_sem provides exclusion between the icache shrinking and the
@@ -482,10 +489,7 @@ static void evict(struct inode *inode)
BUG_ON(!(inode->i_state & I_FREEING));
BUG_ON(!list_empty(&inode->i_lru));

- spin_lock(&inode_lock);
- list_del_init(&inode->i_wb_list);
- spin_unlock(&inode_lock);
-
+ inode_wb_list_del(inode);
inode_sb_list_del(inode);

if (op->evict_inode) {
diff --git a/fs/internal.h b/fs/internal.h
index 7013ae0..b29c46e 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -127,6 +127,11 @@ extern long do_handle_open(int mountdirfd,
*/
extern spinlock_t inode_sb_list_lock;

+/*
+ * fs-writeback.c
+ */
+extern void inode_wb_list_del(struct inode *inode);
+
extern int get_nr_dirty_inodes(void);
extern void evict_inodes(struct super_block *);
extern int invalidate_inodes(struct super_block *, bool);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 0ead399..3f5fee7 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -10,6 +10,7 @@
struct backing_dev_info;

extern spinlock_t inode_lock;
+extern spinlock_t inode_wb_list_lock;

/*
* fs/fs-writeback.c
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 027100d..4b3e9f1 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -73,14 +73,14 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
struct inode *inode;

nr_wb = nr_dirty = nr_io = nr_more_io = 0;
- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
nr_dirty++;
list_for_each_entry(inode, &wb->b_io, i_wb_list)
nr_io++;
list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
nr_more_io++;
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);

global_dirty_limits(&background_thresh, &dirty_thresh);
bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
@@ -682,11 +682,11 @@ void bdi_destroy(struct backing_dev_info *bdi)
if (bdi_has_dirty_io(bdi)) {
struct bdi_writeback *dst = &default_backing_dev_info.wb;

- spin_lock(&inode_lock);
+ spin_lock(&inode_wb_list_lock);
list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
list_splice(&bdi->wb.b_io, &dst->b_io);
list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
- spin_unlock(&inode_lock);
+ spin_unlock(&inode_wb_list_lock);
}

bdi_unregister(bdi);
diff --git a/mm/filemap.c b/mm/filemap.c
index 79b021d..c88d17f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -80,8 +80,8 @@
* ->i_mutex
* ->i_alloc_sem (various)
*
- * ->inode_lock
- * ->sb_lock (fs/fs-writeback.c)
+ * inode_wb_list_lock
+ * sb_lock (fs/fs-writeback.c)
* ->mapping->tree_lock (__sync_single_inode)
*
* ->i_mmap_lock
@@ -98,9 +98,9 @@
* ->zone.lru_lock (check_pte_range->isolate_lru_page)
* ->private_lock (page_remove_rmap->set_page_dirty)
* ->tree_lock (page_remove_rmap->set_page_dirty)
- * ->inode_lock (page_remove_rmap->set_page_dirty)
+ * inode_wb_list_lock (page_remove_rmap->set_page_dirty)
* ->inode->i_lock (page_remove_rmap->set_page_dirty)
- * ->inode_lock (zap_pte_range->set_page_dirty)
+ * inode_wb_list_lock (zap_pte_range->set_page_dirty)
* ->inode->i_lock (zap_pte_range->set_page_dirty)
* ->private_lock (zap_pte_range->__set_page_dirty_buffers)
*
diff --git a/mm/rmap.c b/mm/rmap.c
index 81a95c3..af9e0d7 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -31,12 +31,12 @@
* swap_lock (in swap_duplicate, swap_info_get)
* mmlist_lock (in mmput, drain_mmlist and others)
* mapping->private_lock (in __set_page_dirty_buffers)
- * inode_lock (in set_page_dirty's __mark_inode_dirty)
* inode->i_lock (in set_page_dirty's __mark_inode_dirty)
+ * inode_wb_list_lock (in set_page_dirty's __mark_inode_dirty)
* sb_lock (within inode_lock in fs/fs-writeback.c)
* mapping->tree_lock (widely used, in set_page_dirty,
* in arch-dependent flush_dcache_mmap_lock,
- * within inode_lock in __sync_single_inode)
+ * within inode_wb_list_lock in __sync_single_inode)
*
* (code doesn't rely on that order so it could be switched around)
* ->tasklist_lock
--
1.7.2.3

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