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SubjectRe: [patch 1/7] cpusets: add dirty map to struct address_space
On Tue, 28 Oct 2008, David Rientjes wrote:

> Yeah, if we don't serialize with tree_lock then we'll need to protect the
> attachment of mapping->dirty_nodes with a new spinlock in struct
> address_space (and only for configs where MAX_NUMNODES > BITS_PER_LONG).
> That locking overhead is negligible when mapping->dirty_nodes is non-NULL
> since there's no requirement to protect the setting of the node in the
> nodemask.
>
> Are your concurrent pagecache patches in the latest mmotm? If so, I can
> rebase this entire patchset off that.

We're still taking mapping->tree_lock in both __set_page_dirty() and
__set_page_dirty_nobuffers() in today's mmotm.

When tree_lock is removed with your patchset, we can add a spinlock to
protect mapping->dirty_nodes when MAX_NUMNODES > BITS_PER_LONG.

Would you like to fold this patch into your series (which assumes we're
not taking mapping->tree_lock in either of the two callers above)?
---
diff --git a/fs/inode.c b/fs/inode.c
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -223,6 +223,9 @@ void inode_init_once(struct inode *inode)
INIT_LIST_HEAD(&inode->inotify_watches);
mutex_init(&inode->inotify_mutex);
#endif
+#if MAX_NUMNODES > BITS_PER_LONG
+ spin_lock_init(&inode->i_data.dirty_nodes_lock);
+#endif
}

EXPORT_SYMBOL(inode_init_once);
diff --git a/include/linux/fs.h b/include/linux/fs.h
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -554,6 +554,7 @@ struct address_space {
nodemask_t dirty_nodes; /* nodes with dirty pages */
#else
nodemask_t *dirty_nodes; /* pointer to mask, if dirty */
+ spinlock_t dirty_nodes_lock; /* protects the above */
#endif
#endif
} __attribute__((aligned(sizeof(long))));
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2413,10 +2413,7 @@ EXPORT_SYMBOL_GPL(cpuset_mem_spread_node);
#if MAX_NUMNODES > BITS_PER_LONG
/*
* Special functions for NUMA systems with a large number of nodes. The
- * nodemask is pointed to from the address_space structure. The attachment of
- * the dirty_nodes nodemask is protected by the tree_lock. The nodemask is
- * freed only when the inode is cleared (and therefore unused, thus no locking
- * is necessary).
+ * nodemask is pointed to from the address_space structure.
*/
void cpuset_update_dirty_nodes(struct address_space *mapping,
struct page *page)
@@ -2424,14 +2421,18 @@ void cpuset_update_dirty_nodes(struct address_space *mapping,
nodemask_t *nodes = mapping->dirty_nodes;
int node = page_to_nid(page);

+ spin_lock_irq(&mapping->dirty_nodes_lock);
if (!nodes) {
nodes = kmalloc(sizeof(nodemask_t), GFP_ATOMIC);
- if (!nodes)
+ if (!nodes) {
+ spin_unlock_irq(&mapping->dirty_nodes_lock);
return;
+ }

*nodes = NODE_MASK_NONE;
mapping->dirty_nodes = nodes;
}
+ spin_unlock_irq(&mapping->dirty_nodes_lock);
node_set(node, *nodes);
}

@@ -2446,8 +2447,8 @@ void cpuset_clear_dirty_nodes(struct address_space *mapping)
}

/*
- * Called without tree_lock. The nodemask is only freed when the inode is
- * cleared and therefore this is safe.
+ * The nodemask is only freed when the inode is cleared and therefore this
+ * requires no locking.
*/
int cpuset_intersects_dirty_nodes(struct address_space *mapping,
nodemask_t *mask)

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