Here is a small patch to hash.c
I didn't like the fact that we had a magic number sprinkled through the code so I replaced it with a #define.
I also added some comments.
John
Index: hash.c
===================================================================
--- hash.c (revision 900)
+++ hash.c (working copy)
@@ -1,4 +1,6 @@
-/*
+/* -*- mode: c; c-basic-offset: 8; -*-
+ * vim: noet sw=8 ts=8 ai tw=80 sts=0:
+ *
* hash.c
*
* lockid hash, bh sem hash, inode hash
@@ -95,22 +97,44 @@
#define ocfs_bh_sem_hash_fn(_b) \
(_hashfn((unsigned int)BH_GET_DEVICE((_b)), (_b)->b_blocknr) & ocfs_bh_hash_shift)
+/* How many pages we are allocating for our semaphore hash table */
+#define SEM_HASH_FREE_PAGES 2
+#define SEM_HASH_PAGE_COUNT ( 1 << SEM_HASH_FREE_PAGES )
+
+/*
+ * ocfs_bh_sem_hash_init()
+ *
+ * Setup our buffer head semaphore hash table.
+ *
+ * The purpose of the buffer head semaphore hash table is to store semaphores
+ * for our buffer heads. In order to help speed up the performance of finding
+ * the correct semaphore for our buffer heads we use a hash. The way this is
+ * done is we create a table that has "buckets" of semaphores. Each bucket
+ * contains a list of semaphores for our buffer heads which all have the same
+ * hash value. When we need to find the correct semaphore for a buffer head we
+ * call the ocfs_bh_sem_lookup() function.
+ */
int ocfs_bh_sem_hash_init()
{
int i, ret;
spin_lock_init (&OcfsGlobalCtxt.bh_sem_hash_lock);
- OcfsGlobalCtxt.bh_sem_hash = (struct list_head *)__get_free_pages(GFP_KERNEL, 2);
+ OcfsGlobalCtxt.bh_sem_hash = (struct list_head *)__get_free_pages(GFP_KERNEL, SEM_HASH_FREE_PAGES);
if (!OcfsGlobalCtxt.bh_sem_hash) {
LOG_ERROR_STR("ENOMEM allocating ocfs_bh_sem_hash");
ret = -ENOMEM;
goto bail;
}
- OcfsGlobalCtxt.bh_sem_hash_sz = (PAGE_SIZE * 4) / sizeof(struct list_head);
-
+ /* Keep track of how many buckets we have spots for in our hash table
+ * */
+ OcfsGlobalCtxt.bh_sem_hash_sz = (PAGE_SIZE * SEM_HASH_PAGE_COUNT) / sizeof(struct list_head);
+ /* Setup all our buckets, so that they have properly initialized lists
+ * */
for (i=OcfsGlobalCtxt.bh_sem_hash_sz-1; i>=0; i--)
INIT_LIST_HEAD(&OcfsGlobalCtxt.bh_sem_hash[i]);
+ /* Initially we have no target for pruning and we haven't yet gone
+ * through our pruning function (ocfs_bh_sem_hash_prune) */
atomic_set(&OcfsGlobalCtxt.bh_sem_hash_target_bucket, -1);
atomic_set(&OcfsGlobalCtxt.bh_sem_hash_num_iters, 0);
ret = 0;
@@ -130,7 +154,7 @@
}
spin_lock (&OcfsGlobalCtxt.bh_sem_hash_lock);
- free_pages((unsigned long)OcfsGlobalCtxt.bh_sem_hash, 2);
+ free_pages((unsigned long)OcfsGlobalCtxt.bh_sem_hash, SEM_HASH_FREE_PAGES);
OcfsGlobalCtxt.bh_sem_hash = NULL;
return 0;
-------------- next part --------------
Index: hash.c
===================================================================
--- hash.c (revision 900)
+++ hash.c (working copy)
@@ -1,4 +1,6 @@
-/*
+/* -*- mode: c; c-basic-offset: 8; -*-
+ * vim: noet sw=8 ts=8 ai tw=80 sts=0:
+ *
* hash.c
*
* lockid hash, bh sem hash, inode hash
@@ -95,22 +97,44 @@
#define ocfs_bh_sem_hash_fn(_b) \
(_hashfn((unsigned int)BH_GET_DEVICE((_b)), (_b)->b_blocknr) & ocfs_bh_hash_shift)
+/* How many pages we are allocating for our semaphore hash table */
+#define SEM_HASH_FREE_PAGES 2
+#define SEM_HASH_PAGE_COUNT ( 1 << SEM_HASH_FREE_PAGES )
+
+/*
+ * ocfs_bh_sem_hash_init()
+ *
+ * Setup our buffer head semaphore hash table.
+ *
+ * The purpose of the buffer head semaphore hash table is to store semaphores
+ * for our buffer heads. In order to help speed up the performance of finding
+ * the correct semaphore for our buffer heads we use a hash. The way this is
+ * done is we create a table that has "buckets" of semaphores. Each bucket
+ * contains a list of semaphores for our buffer heads which all have the same
+ * hash value. When we need to find the correct semaphore for a buffer head we
+ * call the ocfs_bh_sem_lookup() function.
+ */
int ocfs_bh_sem_hash_init()
{
int i, ret;
spin_lock_init (&OcfsGlobalCtxt.bh_sem_hash_lock);
- OcfsGlobalCtxt.bh_sem_hash = (struct list_head *)__get_free_pages(GFP_KERNEL, 2);
+ OcfsGlobalCtxt.bh_sem_hash = (struct list_head *)__get_free_pages(GFP_KERNEL, SEM_HASH_FREE_PAGES);
if (!OcfsGlobalCtxt.bh_sem_hash) {
LOG_ERROR_STR("ENOMEM allocating ocfs_bh_sem_hash");
ret = -ENOMEM;
goto bail;
}
- OcfsGlobalCtxt.bh_sem_hash_sz = (PAGE_SIZE * 4) / sizeof(struct list_head);
-
+ /* Keep track of how many buckets we have spots for in our hash table
+ * */
+ OcfsGlobalCtxt.bh_sem_hash_sz = (PAGE_SIZE * SEM_HASH_PAGE_COUNT) / sizeof(struct list_head);
+ /* Setup all our buckets, so that they have properly initialized lists
+ * */
for (i=OcfsGlobalCtxt.bh_sem_hash_sz-1; i>=0; i--)
INIT_LIST_HEAD(&OcfsGlobalCtxt.bh_sem_hash[i]);
+ /* Initially we have no target for pruning and we haven't yet gone
+ * through our pruning function (ocfs_bh_sem_hash_prune) */
atomic_set(&OcfsGlobalCtxt.bh_sem_hash_target_bucket, -1);
atomic_set(&OcfsGlobalCtxt.bh_sem_hash_num_iters, 0);
ret = 0;
@@ -130,7 +154,7 @@
}
spin_lock (&OcfsGlobalCtxt.bh_sem_hash_lock);
- free_pages((unsigned long)OcfsGlobalCtxt.bh_sem_hash, 2);
+ free_pages((unsigned long)OcfsGlobalCtxt.bh_sem_hash, SEM_HASH_FREE_PAGES);
OcfsGlobalCtxt.bh_sem_hash = NULL;
return 0;