linux-kernel - [PATCH 5/7] rhashtable: simplify nested_table_alloc() and rht_bucket_nested

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Date:   Mon, 18 Jun 2018 12:52:50 +1000
From:   NeilBrown <neilb@...e.com>
To:     Thomas Graf <tgraf@...g.ch>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 5/7] rhashtable: simplify nested_table_alloc() and
 rht_bucket_nested_insert()

Now that we don't use the hash value or shift in nested_table_alloc()
there is room for simplification.
We only need to pass a "is this a leaf" flag to nested_table_alloc(),
and don't need to track as much information in
rht_bucket_nested_insert().

Note there is another minor cleanup in nested_table_alloc() here.
The number of elements in a page of "union nested_tables" is most naturally

  PAGE_SIZE / sizeof(ntbl[0])

The previous code had

  PAGE_SIZE / sizeof(ntbl[0].bucket)

which happens to be the correct value only because the bucket uses all
the space in the union.

Acked-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: NeilBrown <neilb@...e.com>
---
 lib/rhashtable.c |   18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index a81cd27d518c..2aa41c15df17 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -116,7 +116,7 @@ static void bucket_table_free_rcu(struct rcu_head *head)
 
 static union nested_table *nested_table_alloc(struct rhashtable *ht,
 					      union nested_table __rcu **prev,
-					      unsigned int shifted)
+					      bool leaf)
 {
 	union nested_table *ntbl;
 	int i;
@@ -127,8 +127,8 @@ static union nested_table *nested_table_alloc(struct rhashtable *ht,
 
 	ntbl = kzalloc(PAGE_SIZE, GFP_ATOMIC);
 
-	if (ntbl && shifted) {
-		for (i = 0; i < PAGE_SIZE / sizeof(ntbl[0].bucket); i++)
+	if (ntbl && leaf) {
+		for (i = 0; i < PAGE_SIZE / sizeof(ntbl[0]); i++)
 			INIT_RHT_NULLS_HEAD(ntbl[i].bucket);
 	}
 
@@ -155,7 +155,7 @@ static struct bucket_table *nested_bucket_table_alloc(struct rhashtable *ht,
 		return NULL;
 
 	if (!nested_table_alloc(ht, (union nested_table __rcu **)tbl->buckets,
-				0)) {
+				false)) {
 		kfree(tbl);
 		return NULL;
 	}
@@ -1207,24 +1207,18 @@ struct rhash_head __rcu **rht_bucket_nested_insert(struct rhashtable *ht,
 	unsigned int index = hash & ((1 << tbl->nest) - 1);
 	unsigned int size = tbl->size >> tbl->nest;
 	union nested_table *ntbl;
-	unsigned int shifted;
-	unsigned int nhash;
 
 	ntbl = (union nested_table *)rcu_dereference_raw(tbl->buckets[0]);
 	hash >>= tbl->nest;
-	nhash = index;
-	shifted = tbl->nest;
 	ntbl = nested_table_alloc(ht, &ntbl[index].table,
-				  size <= (1 << shift) ? shifted : 0);
+				  size <= (1 << shift));
 
 	while (ntbl && size > (1 << shift)) {
 		index = hash & ((1 << shift) - 1);
 		size >>= shift;
 		hash >>= shift;
-		nhash |= index << shifted;
-		shifted += shift;
 		ntbl = nested_table_alloc(ht, &ntbl[index].table,
-					  size <= (1 << shift) ? shifted : 0);
+					  size <= (1 << shift));
 	}
 
 	if (!ntbl)