linux-kernel - [PATCH] dcache: Deduplicate code that sets up dentry

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Date:	Tue, 22 Sep 2015 23:56:51 -0500
From:	Eric Biggers <ebiggers3@...il.com>
To:	linux-fsdevel@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Eric Biggers <ebiggers3@...il.com>
Subject: [PATCH] dcache: Deduplicate code that sets up dentry_hashtable

Make both dcache_init_early() and dcache_init() call a new helper
function, dcache_alloc_hashtable().  Also address a small inefficiency by
moving the table length calculation outside of the loop condition.  gcc
apparently doesn't do that because it assumes that the memory pointed to
by 'dentry_hashtable' might alias 'd_hash_shift'.

Signed-off-by: Eric Biggers <ebiggers3@...il.com>
---
 fs/dcache.c | 48 +++++++++++++++++++-----------------------------
 1 file changed, 19 insertions(+), 29 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 5c33aeb..7cfe848 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3380,35 +3380,39 @@ static int __init set_dhash_entries(char *str)
 }
 __setup("dhash_entries=", set_dhash_entries);
 
-static void __init dcache_init_early(void)
+static void __init dcache_alloc_hashtable(int flags)
 {
-	unsigned int loop;
-
-	/* If hashes are distributed across NUMA nodes, defer
-	 * hash allocation until vmalloc space is available.
-	 */
-	if (hashdist)
-		return;
+	unsigned int num_entries;
+	unsigned int i;
 
 	dentry_hashtable =
 		alloc_large_system_hash("Dentry cache",
 					sizeof(struct hlist_bl_head),
 					dhash_entries,
 					13,
-					HASH_EARLY,
+					flags,
 					&d_hash_shift,
 					&d_hash_mask,
 					0,
 					0);
 
-	for (loop = 0; loop < (1U << d_hash_shift); loop++)
-		INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
+	num_entries = 1U << d_hash_shift;
+
+	for (i = 0; i < num_entries; i++)
+		INIT_HLIST_BL_HEAD(&dentry_hashtable[i]);
 }
 
-static void __init dcache_init(void)
+static void __init dcache_init_early(void)
 {
-	unsigned int loop;
+	/* If hashes are distributed across NUMA nodes, defer
+	 * hash allocation until vmalloc space is available.
+	 */
+	if (!hashdist)
+		dcache_alloc_hashtable(HASH_EARLY);
+}
 
+static void __init dcache_init(void)
+{
 	/* 
 	 * A constructor could be added for stable state like the lists,
 	 * but it is probably not worth it because of the cache nature
@@ -3418,22 +3422,8 @@ static void __init dcache_init(void)
 		SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
 
 	/* Hash may have been set up in dcache_init_early */
-	if (!hashdist)
-		return;
-
-	dentry_hashtable =
-		alloc_large_system_hash("Dentry cache",
-					sizeof(struct hlist_bl_head),
-					dhash_entries,
-					13,
-					0,
-					&d_hash_shift,
-					&d_hash_mask,
-					0,
-					0);
-
-	for (loop = 0; loop < (1U << d_hash_shift); loop++)
-		INIT_HLIST_BL_HEAD(dentry_hashtable + loop);
+	if (hashdist)
+		dcache_alloc_hashtable(0);
 }
 
 /* SLAB cache for __getname() consumers */
-- 
2.4.3

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