The patch increases the parallelism of mb_cache_entry utilization by
replacing list_head with hlist_bl_node for the implementation of both the
block and index hash tables. Each hlist_bl_node contains a built-in lock
used to protect mb_cache's local block and index hash chains. The global
data mb_cache_lru_list and mb_cache_list continue to be protected by the
global mb_cache_spinlock.
A new spinlock is also added to the mb_cache_entry to protect its local data,
e_used and e_queued.
Signed-off-by: T. Makphaibulchoke <tmac@xxxxxx>
---
fs/mbcache.c | 363 ++++++++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 260 insertions(+), 103 deletions(-)
diff --git a/fs/mbcache.c b/fs/mbcache.c
index 55db0da..0c4cec2 100644
--- a/fs/mbcache.c
+++ b/fs/mbcache.c
@@ -26,6 +26,40 @@
* back on the lru list.
*/
+/*
+ * Lock descriptions and usage:
+ *
+ * Each hash chain of both the block and index hash tables now contains
+ * a built-in lock used to serialize accesses to the hash chain.
+ *
+ * Accesses to global data structures mb_cache_list and mb_cache_lru_list
+ * are serialized via the global spinlock mb_cache_spinlock.
+ *
+ * Each mb_cache_entry contains a spinlock, e_entry_lock, to serialize
+ * accesses to its local data, such as e_used and e_queued.
+ *
+ * Lock ordering:
+ *
+ * mb_cache_spinlock has the lock highest order, followed by each block and
+ * index hash chain's lock, with e_entry_lock the lowest. While holding
+ * mb_cache_spinlock, a thread can acquire either a block and/or index hash
+ * chain lock, and in turn can also acquire each entry spinlock, e_entry_lock.
+ *
+ * Synchronization:
+ *
+ * Since both mb_cache_entry_get and mb_cache_entry_find scan the block and
+ * index hash chian, it needs to lock the corresponding hash chain. For each
+ * mb_cache_entry within the chain, it needs to lock the mb_cache_entry to
+ * prevent either any simultaneous release or free on the entry and also
+ * to serialize accesses to either the e_used or e_queued member of the entry.
+ *
+ * To avoid having a dangling reference to an already freed
+ * mb_cache_entry, an mb_cache_entry is only freed when it is not on a
+ * block hash chain and also no longer being referenced, both e_used,
+ * and e_queued are 0's. When an mb_cache_entry is explicitly freed it is
+ * first removed from a block hash chain.
+ */
+
#include <linux/kernel.h>
#include <linux/module.h>
@@ -113,11 +147,21 @@ __mb_cache_entry_unhash_index(struct mb_cache_entry *ce)
hlist_bl_del_init(&ce->e_index.o_list);
}
+/*
+ * __mb_cache_entry_unhash_unlock()
+ *
+ * This function is called to unhash both the block and index hash
+ * chain.
+ * It assumes both the block and index hash chain is locked upon entry.
+ * It also unlock both hash chains both exit
+ */
static inline void
-__mb_cache_entry_unhash(struct mb_cache_entry *ce)
+__mb_cache_entry_unhash_unlock(struct mb_cache_entry *ce)
{
__mb_cache_entry_unhash_index(ce);
+ hlist_bl_unlock(ce->e_index_hash_p);
__mb_cache_entry_unhash_block(ce);
+ hlist_bl_unlock(ce->e_block_hash_p);
}
static void
@@ -130,31 +174,42 @@ __mb_cache_entry_forget(struct mb_cache_entry *ce, gfp_t gfp_mask)
atomic_dec(&cache->c_entry_count);
}
-
static void
-__mb_cache_entry_release_unlock(struct mb_cache_entry *ce)
- __releases(mb_cache_spinlock)
+__mb_cache_entry_release(struct mb_cache_entry *ce)
{
+ /* First lock the entry to serialize access to its local data. */
+ spin_lock(&ce->e_entry_lock);
/* Wake up all processes queuing for this cache entry. */
if (ce->e_queued)
wake_up_all(&mb_cache_queue);
if (ce->e_used >= MB_CACHE_WRITER)
ce->e_used -= MB_CACHE_WRITER;
+ /*
+ * Make sure that all cache entries on lru_list have
+ * both e_used and e_qued of 0s.
+ */
ce->e_used--;
if (!(ce->e_used || ce->e_queued)) {
- if (!__mb_cache_entry_is_block_hashed(ce))
+ if (!__mb_cache_entry_is_block_hashed(ce)) {
+ spin_unlock(&ce->e_entry_lock);
goto forget;
- mb_assert(list_empty(&ce->e_lru_list));
- list_add_tail(&ce->e_lru_list, &mb_cache_lru_list);
+ }
+ /*
+ * Need access to lru list, first drop entry lock,
+ * then reacquire the lock in the proper order.
+ */
+ spin_lock(&mb_cache_spinlock);
+ if (list_empty(&ce->e_lru_list))
+ list_add_tail(&ce->e_lru_list, &mb_cache_lru_list);
+ spin_unlock(&mb_cache_spinlock);
}
- spin_unlock(&mb_cache_spinlock);
+ spin_unlock(&ce->e_entry_lock);
return;
forget:
- spin_unlock(&mb_cache_spinlock);
+ mb_assert(list_empty(&ce->e_lru_list));
__mb_cache_entry_forget(ce, GFP_KERNEL);
}
-
/*
* mb_cache_shrink_scan() memory pressure callback
*
@@ -177,17 +232,32 @@ mb_cache_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
mb_debug("trying to free %d entries", nr_to_scan);
spin_lock(&mb_cache_spinlock);
- while (nr_to_scan-- && !list_empty(&mb_cache_lru_list)) {
+ while ((nr_to_scan-- > 0) && !list_empty(&mb_cache_lru_list)) {
struct mb_cache_entry *ce =
list_entry(mb_cache_lru_list.next,
- struct mb_cache_entry, e_lru_list);
- list_move_tail(&ce->e_lru_list, &free_list);
- __mb_cache_entry_unhash(ce);
- freed++;
+ struct mb_cache_entry, e_lru_list);
+ list_del_init(&ce->e_lru_list);
+ spin_unlock(&mb_cache_spinlock);
+ /* Prevent any find or get operation on the entry */
+ hlist_bl_lock(ce->e_block_hash_p);
+ hlist_bl_lock(ce->e_index_hash_p);
+ /* Ignore if it is touched by a find/get */
+ if (ce->e_used || ce->e_queued ||
+ !list_empty(&ce->e_lru_list)) {
+ hlist_bl_unlock(ce->e_index_hash_p);
+ hlist_bl_unlock(ce->e_block_hash_p);
+ spin_lock(&mb_cache_spinlock);
+ continue;
+ }
+ __mb_cache_entry_unhash_unlock(ce);
+ list_add_tail(&ce->e_lru_list, &free_list);
+ spin_lock(&mb_cache_spinlock);
}
spin_unlock(&mb_cache_spinlock);
+
list_for_each_entry_safe(entry, tmp, &free_list, e_lru_list) {
__mb_cache_entry_forget(entry, gfp_mask);
+ freed++;
}
return freed;
}
@@ -290,21 +360,41 @@ void
mb_cache_shrink(struct block_device *bdev)
{
LIST_HEAD(free_list);
- struct list_head *l, *ltmp;
+ struct list_head *l;
+ struct mb_cache_entry *ce, *tmp;
+ l = &mb_cache_lru_list;
spin_lock(&mb_cache_spinlock);
- list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
- struct mb_cache_entry *ce =
- list_entry(l, struct mb_cache_entry, e_lru_list);
+ while (!list_is_last(l, &mb_cache_lru_list)) {
+ l = l->next;
+ ce = list_entry(l, struct mb_cache_entry, e_lru_list);
if (ce->e_bdev == bdev) {
- list_move_tail(&ce->e_lru_list, &free_list);
- __mb_cache_entry_unhash(ce);
+ list_del_init(&ce->e_lru_list);
+ spin_unlock(&mb_cache_spinlock);
+ /*
+ * Prevent any find or get operation on the entry.
+ */
+ hlist_bl_lock(ce->e_block_hash_p);
+ hlist_bl_lock(ce->e_index_hash_p);
+ /* Ignore if it is touched by a find/get */
+ if (ce->e_used || ce->e_queued ||
+ !list_empty(&ce->e_lru_list)) {
+ hlist_bl_unlock(ce->e_index_hash_p);
+ hlist_bl_unlock(ce->e_block_hash_p);
+ l = &mb_cache_lru_list;
+ spin_lock(&mb_cache_spinlock);
+ continue;
+ }
+ __mb_cache_entry_unhash_unlock(ce);
+ list_add_tail(&ce->e_lru_list, &free_list);
+ l = &mb_cache_lru_list;
+ spin_lock(&mb_cache_spinlock);
}
}
spin_unlock(&mb_cache_spinlock);
- list_for_each_safe(l, ltmp, &free_list) {
- __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
- e_lru_list), GFP_KERNEL);
+
+ list_for_each_entry_safe(ce, tmp, &free_list, e_lru_list) {
+ __mb_cache_entry_forget(ce, GFP_KERNEL);
}
}
@@ -320,23 +410,26 @@ void
mb_cache_destroy(struct mb_cache *cache)
{
LIST_HEAD(free_list);
- struct list_head *l, *ltmp;
+ struct mb_cache_entry *ce, *tmp;
spin_lock(&mb_cache_spinlock);
- list_for_each_safe(l, ltmp, &mb_cache_lru_list) {
- struct mb_cache_entry *ce =
- list_entry(l, struct mb_cache_entry, e_lru_list);
- if (ce->e_cache == cache) {
+ list_for_each_entry_safe(ce, tmp, &mb_cache_lru_list, e_lru_list) {
+ if (ce->e_cache == cache)
list_move_tail(&ce->e_lru_list, &free_list);
- __mb_cache_entry_unhash(ce);
- }
}
list_del(&cache->c_cache_list);
spin_unlock(&mb_cache_spinlock);
- list_for_each_safe(l, ltmp, &free_list) {
- __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
- e_lru_list), GFP_KERNEL);
+ list_for_each_entry_safe(ce, tmp, &free_list, e_lru_list) {
+ list_del_init(&ce->e_lru_list);
+ /*
+ * Prevent any find or get operation on the entry.
+ */
+ hlist_bl_lock(ce->e_block_hash_p);
+ hlist_bl_lock(ce->e_index_hash_p);
+ mb_assert(!(ce->e_used || ce->e_queued));
+ __mb_cache_entry_unhash_unlock(ce);
+ __mb_cache_entry_forget(ce, GFP_KERNEL);
}
if (atomic_read(&cache->c_entry_count) > 0) {
@@ -363,31 +456,56 @@ mb_cache_destroy(struct mb_cache *cache)
struct mb_cache_entry *
mb_cache_entry_alloc(struct mb_cache *cache, gfp_t gfp_flags)
{
- struct mb_cache_entry *ce = NULL;
+ struct mb_cache_entry *ce;
if (atomic_read(&cache->c_entry_count) >= cache->c_max_entries) {
+ struct list_head *l;
+
+ l = &mb_cache_lru_list;
spin_lock(&mb_cache_spinlock);
- if (!list_empty(&mb_cache_lru_list)) {
- ce = list_entry(mb_cache_lru_list.next,
- struct mb_cache_entry, e_lru_list);
- list_del_init(&ce->e_lru_list);
- __mb_cache_entry_unhash(ce);
+ while (!list_is_last(l, &mb_cache_lru_list)) {
+ l = l->next;
+ ce = list_entry(l, struct mb_cache_entry, e_lru_list);
+ if (ce->e_cache == cache) {
+ list_del_init(&ce->e_lru_list);
+ spin_unlock(&mb_cache_spinlock);
+ /*
+ * Prevent any find or get operation on the
+ * entry.
+ */
+ hlist_bl_lock(ce->e_block_hash_p);
+ hlist_bl_lock(ce->e_index_hash_p);
+ /* Ignore if it is touched by a find/get */
+ if (ce->e_used || ce->e_queued ||
+ !list_empty(&ce->e_lru_list)) {
+ hlist_bl_unlock(ce->e_index_hash_p);
+ hlist_bl_unlock(ce->e_block_hash_p);
+ l = &mb_cache_lru_list;
+ spin_lock(&mb_cache_spinlock);
+ continue;
+ }
+ mb_assert(list_empty(&ce->e_lru_list));
+ mb_assert(!(ce->e_used || ce->e_queued));
+ __mb_cache_entry_unhash_unlock(ce);
+ goto found;
+ }
}
spin_unlock(&mb_cache_spinlock);
}
- if (!ce) {
- ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags);
- if (!ce)
- return NULL;
- atomic_inc(&cache->c_entry_count);
- INIT_LIST_HEAD(&ce->e_lru_list);
- INIT_HLIST_BL_NODE(&ce->e_block_list);
- INIT_HLIST_BL_NODE(&ce->e_index.o_list);
- ce->e_cache = cache;
- ce->e_queued = 0;
- }
+
+ ce = kmem_cache_alloc(cache->c_entry_cache, gfp_flags);
+ if (!ce)
+ return NULL;
+ atomic_inc(&cache->c_entry_count);
+ INIT_LIST_HEAD(&ce->e_lru_list);
+ INIT_HLIST_BL_NODE(&ce->e_block_list);
+ INIT_HLIST_BL_NODE(&ce->e_index.o_list);
+ ce->e_cache = cache;
+ ce->e_queued = 0;
+found:
ce->e_block_hash_p = &cache->c_block_hash[0];
ce->e_index_hash_p = &cache->c_index_hash[0];
+ spin_lock_init(&ce->e_entry_lock);
ce->e_used = 1 + MB_CACHE_WRITER;
return ce;
}
@@ -423,25 +541,28 @@ mb_cache_entry_insert(struct mb_cache_entry *ce, struct block_device *bdev,
bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
cache->c_bucket_bits);
block_hash_p = &cache->c_block_hash[bucket];
- spin_lock(&mb_cache_spinlock);
+ hlist_bl_lock(block_hash_p);
hlist_bl_for_each_entry(lce, l, block_hash_p, e_block_list) {
if (lce->e_bdev == bdev && lce->e_block == block)
goto out;
}
mb_assert(!__mb_cache_entry_is_block_hashed(ce));
- __mb_cache_entry_unhash(ce);
+ __mb_cache_entry_unhash_block(ce);
+ __mb_cache_entry_unhash_index(ce);
ce->e_bdev = bdev;
ce->e_block = block;
ce->e_block_hash_p = block_hash_p;
ce->e_index.o_key = key;
bucket = hash_long(key, cache->c_bucket_bits);
index_hash_p = &cache->c_index_hash[bucket];
+ hlist_bl_lock(index_hash_p);
ce->e_index_hash_p = index_hash_p;
hlist_bl_add_head(&ce->e_index.o_list, index_hash_p);
hlist_bl_add_head(&ce->e_block_list, block_hash_p);
+ hlist_bl_unlock(index_hash_p);
error = 0;
out:
- spin_unlock(&mb_cache_spinlock);
+ hlist_bl_unlock(block_hash_p);
return error;
}
@@ -456,24 +577,26 @@ out:
void
mb_cache_entry_release(struct mb_cache_entry *ce)
{
- spin_lock(&mb_cache_spinlock);
- __mb_cache_entry_release_unlock(ce);
+ __mb_cache_entry_release(ce);
}
/*
* mb_cache_entry_free()
*
- * This is equivalent to the sequence mb_cache_entry_takeout() --
- * mb_cache_entry_release().
*/
void
mb_cache_entry_free(struct mb_cache_entry *ce)
{
- spin_lock(&mb_cache_spinlock);
+ mb_assert(ce);
mb_assert(list_empty(&ce->e_lru_list));
- __mb_cache_entry_unhash(ce);
- __mb_cache_entry_release_unlock(ce);
+ hlist_bl_lock(ce->e_index_hash_p);
+ __mb_cache_entry_unhash_index(ce);
+ hlist_bl_unlock(ce->e_index_hash_p);
+ hlist_bl_lock(ce->e_block_hash_p);
+ __mb_cache_entry_unhash_block(ce);
+ hlist_bl_unlock(ce->e_block_hash_p);
+ __mb_cache_entry_release(ce);
}
@@ -493,43 +616,58 @@ mb_cache_entry_get(struct mb_cache *cache, struct block_device *bdev,
struct hlist_bl_node *l;
struct mb_cache_entry *ce;
struct hlist_bl_head *block_hash_p;
+ int held_lock = 1;
bucket = hash_long((unsigned long)bdev + (block & 0xffffffff),
cache->c_bucket_bits);
block_hash_p = &cache->c_block_hash[bucket];
- spin_lock(&mb_cache_spinlock);
+ /* First serialize access to the block corresponding hash chain. */
+ hlist_bl_lock(block_hash_p);
hlist_bl_for_each_entry(ce, l, block_hash_p, e_block_list) {
mb_assert(ce->e_block_hash_p == block_hash_p);
if (ce->e_bdev == bdev && ce->e_block == block) {
- DEFINE_WAIT(wait);
-
- if (!list_empty(&ce->e_lru_list))
+ /*
+ * Prevent a release on the entry.
+ */
+ spin_lock(&ce->e_entry_lock);
+ if (!list_empty(&ce->e_lru_list)) {
+ spin_lock(&mb_cache_spinlock);
list_del_init(&ce->e_lru_list);
-
- while (ce->e_used > 0) {
- ce->e_queued++;
- prepare_to_wait(&mb_cache_queue, &wait,
- TASK_UNINTERRUPTIBLE);
spin_unlock(&mb_cache_spinlock);
- schedule();
- spin_lock(&mb_cache_spinlock);
- ce->e_queued--;
}
- finish_wait(&mb_cache_queue, &wait);
+ if (ce->e_used > 0) {
+ DEFINE_WAIT(wait);
+ while (ce->e_used > 0) {
+ ce->e_queued++;
+ prepare_to_wait(&mb_cache_queue, &wait,
+ TASK_UNINTERRUPTIBLE);
+ spin_unlock(&ce->e_entry_lock);
+ if (held_lock) {
+ hlist_bl_unlock(block_hash_p);
+ held_lock = 0;
+ }
+ schedule();
+ spin_lock(&ce->e_entry_lock);
+ ce->e_queued--;
+ }
+ finish_wait(&mb_cache_queue, &wait);
+ }
ce->e_used += 1 + MB_CACHE_WRITER;
+ spin_unlock(&ce->e_entry_lock);
if (!__mb_cache_entry_is_block_hashed(ce)) {
- __mb_cache_entry_release_unlock(ce);
+ if (held_lock)
+ hlist_bl_unlock(block_hash_p);
+ __mb_cache_entry_release(ce);
return NULL;
}
- goto cleanup;
+ if (held_lock)
+ hlist_bl_unlock(block_hash_p);
+ return ce;
}
}
- ce = NULL;
-
-cleanup:
- spin_unlock(&mb_cache_spinlock);
- return ce;
+ hlist_bl_unlock(block_hash_p);
+ return NULL;
}
#if !defined(MB_CACHE_INDEXES_COUNT) || (MB_CACHE_INDEXES_COUNT > 0)
@@ -538,40 +676,59 @@ static struct mb_cache_entry *
__mb_cache_entry_find(struct hlist_bl_node *l, struct hlist_bl_head *head,
struct block_device *bdev, unsigned int key)
{
+ int held_lock = 1;
+
+ /* The index hash chain is alredy acquire by caller. */
while (l != NULL) {
struct mb_cache_entry *ce =
hlist_bl_entry(l, struct mb_cache_entry,
e_index.o_list);
mb_assert(ce->e_index_hash_p == head);
if (ce->e_bdev == bdev && ce->e_index.o_key == key) {
- DEFINE_WAIT(wait);
-
- if (!list_empty(&ce->e_lru_list))
+ /*
+ * Prevent a release on the entry.
+ */
+ spin_lock(&ce->e_entry_lock);
+ if (!list_empty(&ce->e_lru_list)) {
+ spin_lock(&mb_cache_spinlock);
list_del_init(&ce->e_lru_list);
-
+ spin_unlock(&mb_cache_spinlock);
+ }
+ ce->e_used++;
/* Incrementing before holding the lock gives readers
priority over writers. */
- ce->e_used++;
- while (ce->e_used >= MB_CACHE_WRITER) {
- ce->e_queued++;
- prepare_to_wait(&mb_cache_queue, &wait,
- TASK_UNINTERRUPTIBLE);
- spin_unlock(&mb_cache_spinlock);
- schedule();
- spin_lock(&mb_cache_spinlock);
- ce->e_queued--;
+ if (ce->e_used >= MB_CACHE_WRITER) {
+ DEFINE_WAIT(wait);
+
+ while (ce->e_used >= MB_CACHE_WRITER) {
+ ce->e_queued++;
+ prepare_to_wait(&mb_cache_queue, &wait,
+ TASK_UNINTERRUPTIBLE);
+ spin_unlock(&ce->e_entry_lock);
+ if (held_lock) {
+ hlist_bl_unlock(head);
+ held_lock = 0;
+ }
+ schedule();
+ spin_lock(&ce->e_entry_lock);
+ ce->e_queued--;
+ }
+ finish_wait(&mb_cache_queue, &wait);
}
- finish_wait(&mb_cache_queue, &wait);
-
+ spin_unlock(&ce->e_entry_lock);
if (!__mb_cache_entry_is_block_hashed(ce)) {
- __mb_cache_entry_release_unlock(ce);
- spin_lock(&mb_cache_spinlock);
+ if (held_lock)
+ hlist_bl_unlock(head);
+ __mb_cache_entry_release(ce);
return ERR_PTR(-EAGAIN);
}
+ if (held_lock)
+ hlist_bl_unlock(head);
return ce;
}
l = l->next;
}
+ hlist_bl_unlock(head);
return NULL;
}
@@ -598,12 +755,12 @@ mb_cache_entry_find_first(struct mb_cache *cache, struct block_device *bdev,
struct hlist_bl_head *index_hash_p;
index_hash_p = &cache->c_index_hash[bucket];
- spin_lock(&mb_cache_spinlock);
+ hlist_bl_lock(index_hash_p);
if (!hlist_bl_empty(index_hash_p)) {
l = hlist_bl_first(index_hash_p);
ce = __mb_cache_entry_find(l, index_hash_p, bdev, key);
- }
- spin_unlock(&mb_cache_spinlock);
+ } else
+ hlist_bl_unlock(index_hash_p);
return ce;
}
@@ -638,11 +795,11 @@ mb_cache_entry_find_next(struct mb_cache_entry *prev,
index_hash_p = &cache->c_index_hash[bucket];
mb_assert(prev->e_index_hash_p == index_hash_p);
- spin_lock(&mb_cache_spinlock);
+ hlist_bl_lock(index_hash_p);
mb_assert(!hlist_bl_empty(index_hash_p));
l = prev->e_index.o_list.next;
ce = __mb_cache_entry_find(l, index_hash_p, bdev, key);
- __mb_cache_entry_release_unlock(prev);
+ __mb_cache_entry_release(prev);
return ce;
}
--
1.7.11.3
--
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