mm, truncate: do not check mapping for every page being truncated

During truncation, the mapping has already been checked for shmem and
dax so it's known that workingset_update_node is required.

This patch avoids the checks on mapping for each page being truncated.
In all other cases, a lookup helper is used to determine if
workingset_update_node() needs to be called.  The one danger is that the
API is slightly harder to use as calling workingset_update_node directly
without checking for dax or shmem mappings could lead to surprises.
However, the API rarely needs to be used and hopefully the comment is
enough to give people the hint.

sparsetruncate (tiny)
                              4.14.0-rc4             4.14.0-rc4
                             oneirq-v1r1        pickhelper-v1r1
Min          Time      141.00 (   0.00%)      140.00 (   0.71%)
1st-qrtle    Time      142.00 (   0.00%)      141.00 (   0.70%)
2nd-qrtle    Time      142.00 (   0.00%)      142.00 (   0.00%)
3rd-qrtle    Time      143.00 (   0.00%)      143.00 (   0.00%)
Max-90%      Time      144.00 (   0.00%)      144.00 (   0.00%)
Max-95%      Time      147.00 (   0.00%)      145.00 (   1.36%)
Max-99%      Time      195.00 (   0.00%)      191.00 (   2.05%)
Max          Time      230.00 (   0.00%)      205.00 (  10.87%)
Amean        Time      144.37 (   0.00%)      143.82 (   0.38%)
Stddev       Time       10.44 (   0.00%)        9.00 (  13.74%)
Coeff        Time        7.23 (   0.00%)        6.26 (  13.41%)
Best99%Amean Time      143.72 (   0.00%)      143.34 (   0.26%)
Best95%Amean Time      142.37 (   0.00%)      142.00 (   0.26%)
Best90%Amean Time      142.19 (   0.00%)      141.85 (   0.24%)
Best75%Amean Time      141.92 (   0.00%)      141.58 (   0.24%)
Best50%Amean Time      141.69 (   0.00%)      141.31 (   0.27%)
Best25%Amean Time      141.38 (   0.00%)      140.97 (   0.29%)

As you'd expect, the gain is marginal but it can be detected.  The
differences in bonnie are all within the noise which is not surprising
given the impact on the microbenchmark.

radix_tree_update_node_t is a callback for some radix operations that
optionally passes in a private field.  The only user of the callback is
workingset_update_node and as it no longer requires a mapping, the
private field is removed.

Link: http://lkml.kernel.org/r/20171018075952.10627-3-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 14 insertions, 18 deletions

diff --git a/lib/idr.c b/lib/idr.c
index edd9b2b..2593ce5 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -171,7 +171,7 @@ void *idr_replace_ext(struct idr *idr, void *ptr, unsigned long id)
 	if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
 		return ERR_PTR(-ENOENT);
 
-	__radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL, NULL);
+	__radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL);
 
 	return entry;
 }
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 8b1feca..c8d5556 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -677,8 +677,7 @@ out:
  *	@root		radix tree root
  */
 static inline bool radix_tree_shrink(struct radix_tree_root *root,
-				     radix_tree_update_node_t update_node,
-				     void *private)
+				     radix_tree_update_node_t update_node)
 {
 	bool shrunk = false;
 
@@ -739,7 +738,7 @@ static inline bool radix_tree_shrink(struct radix_tree_root *root,
 		if (!radix_tree_is_internal_node(child)) {
 			node->slots[0] = (void __rcu *)RADIX_TREE_RETRY;
 			if (update_node)
-				update_node(node, private);
+				update_node(node);
 		}
 
 		WARN_ON_ONCE(!list_empty(&node->private_list));
@@ -752,7 +751,7 @@ static inline bool radix_tree_shrink(struct radix_tree_root *root,
 
 static bool delete_node(struct radix_tree_root *root,
 			struct radix_tree_node *node,
-			radix_tree_update_node_t update_node, void *private)
+			radix_tree_update_node_t update_node)
 {
 	bool deleted = false;
 
@@ -762,8 +761,8 @@ static bool delete_node(struct radix_tree_root *root,
 		if (node->count) {
 			if (node_to_entry(node) ==
 					rcu_dereference_raw(root->rnode))
-				deleted |= radix_tree_shrink(root, update_node,
-								private);
+				deleted |= radix_tree_shrink(root,
+								update_node);
 			return deleted;
 		}
 
@@ -1173,7 +1172,6 @@ static int calculate_count(struct radix_tree_root *root,
  * @slot:		pointer to slot in @node
  * @item:		new item to store in the slot.
  * @update_node:	callback for changing leaf nodes
- * @private:		private data to pass to @update_node
  *
  * For use with __radix_tree_lookup().  Caller must hold tree write locked
  * across slot lookup and replacement.
@@ -1181,7 +1179,7 @@ static int calculate_count(struct radix_tree_root *root,
 void __radix_tree_replace(struct radix_tree_root *root,
 			  struct radix_tree_node *node,
 			  void __rcu **slot, void *item,
-			  radix_tree_update_node_t update_node, void *private)
+			  radix_tree_update_node_t update_node)
 {
 	void *old = rcu_dereference_raw(*slot);
 	int exceptional = !!radix_tree_exceptional_entry(item) -
@@ -1201,9 +1199,9 @@ void __radix_tree_replace(struct radix_tree_root *root,
 		return;
 
 	if (update_node)
-		update_node(node, private);
+		update_node(node);
 
-	delete_node(root, node, update_node, private);
+	delete_node(root, node, update_node);
 }
 
 /**
@@ -1225,7 +1223,7 @@ void __radix_tree_replace(struct radix_tree_root *root,
 void radix_tree_replace_slot(struct radix_tree_root *root,
 			     void __rcu **slot, void *item)
 {
-	__radix_tree_replace(root, NULL, slot, item, NULL, NULL);
+	__radix_tree_replace(root, NULL, slot, item, NULL);
 }
 EXPORT_SYMBOL(radix_tree_replace_slot);
 
@@ -1242,7 +1240,7 @@ void radix_tree_iter_replace(struct radix_tree_root *root,
 				const struct radix_tree_iter *iter,
 				void __rcu **slot, void *item)
 {
-	__radix_tree_replace(root, iter->node, slot, item, NULL, NULL);
+	__radix_tree_replace(root, iter->node, slot, item, NULL);
 }
 
 #ifdef CONFIG_RADIX_TREE_MULTIORDER
@@ -1972,7 +1970,6 @@ EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);
  *	@root:		radix tree root
  *	@node:		node containing @index
  *	@update_node:	callback for changing leaf nodes
- *	@private:	private data to pass to @update_node
  *
  *	After clearing the slot at @index in @node from radix tree
  *	rooted at @root, call this function to attempt freeing the
@@ -1980,10 +1977,9 @@ EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);
  */
 void __radix_tree_delete_node(struct radix_tree_root *root,
 			      struct radix_tree_node *node,
-			      radix_tree_update_node_t update_node,
-			      void *private)
+			      radix_tree_update_node_t update_node)
 {
-	delete_node(root, node, update_node, private);
+	delete_node(root, node, update_node);
 }
 
 static bool __radix_tree_delete(struct radix_tree_root *root,
@@ -2001,7 +1997,7 @@ static bool __radix_tree_delete(struct radix_tree_root *root,
 			node_tag_clear(root, node, tag, offset);
 
 	replace_slot(slot, NULL, node, -1, exceptional);
-	return node && delete_node(root, node, NULL, NULL);
+	return node && delete_node(root, node, NULL);
 }
 
 /**