[PATCH 36/40] fscache: convert operation to use workqueue instead of slow-work

Tejun Heo
2010-01-18T01:02:05Z

Make fscache operation to use only workqueue instead of combination of
workqueue and slow-work. FSCACHE_OP_SLOW is dropped and
FSCACHE_OP_FAST is renamed to FSCACHE_OP_ASYNC and uses newly added
fscache_op_wq workqueue to execute op->processor().
fscache_operation_init_slow() is dropped and fscache_operation_init()
now takes @processor argument directly.

* fscache_retrieval_work() is no longer necessary as OP_ASYNC now does
the equivalent thing.

* Max concurrency for objects is set to 4 which is the default for
slow works. API to adjust cwq max concurrency limit can be added
easily.

* Single CPU workqueue was used to ease conversion. If necessary,
multi CPU one can be used by adding per-operation mutex.

NOT_SIGNED_OFF_YET
Cc: David Howells <dhowells@redhat.com>
---
fs/cachefiles/rdwr.c | 4 +-
fs/fscache/internal.h | 1 +
fs/fscache/main.c | 9 +++++
fs/fscache/operation.c | 67 +++++------------------------------------
fs/fscache/page.c | 36 +++++-----------------
include/linux/fscache-cache.h | 34 +++++---------------
6 files changed, 37 insertions(+), 114 deletions(-)

diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index 1d83325..43bbe57 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -421,7 +421,7 @@ int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;

op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
- op->op.flags |= FSCACHE_OP_FAST;
+ op->op.flags |= FSCACHE_OP_ASYNC;
op->op.processor = cachefiles_read_copier;

pagevec_init(&pagevec, 0);
@@ -728,7 +728,7 @@ int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
pagevec_init(&pagevec, 0);

op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
- op->op.flags |= FSCACHE_OP_FAST;
+ op->op.flags |= FSCACHE_OP_ASYNC;
op->op.processor = cachefiles_read_copier;

INIT_LIST_HEAD(&backpages);
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index f9da2fc..4238ce6 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -83,6 +83,7 @@ extern unsigned fscache_defer_create;
extern unsigned fscache_debug;
extern struct kobject *fscache_root;
extern struct workqueue_struct *fscache_object_wq;
+extern struct workqueue_struct *fscache_op_wq;

extern int fscache_wait_bit(void *);
extern int fscache_wait_bit_interruptible(void *);
diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index a676a86..908803c 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -41,6 +41,7 @@ MODULE_PARM_DESC(fscache_debug,

struct kobject *fscache_root;
struct workqueue_struct *fscache_object_wq;
+struct workqueue_struct *fscache_op_wq;

/*
* initialise the fs caching module
@@ -59,6 +60,11 @@ static int __init fscache_init(void)
if (!fscache_object_wq)
goto error_object_wq;

+ fscache_op_wq =
+ __create_workqueue("fscache_operation", WQ_SINGLE_CPU, 4);
+ if (!fscache_op_wq)
+ goto error_op_wq;
+
ret = fscache_proc_init();
if (ret < 0)
goto error_proc;
@@ -87,6 +93,8 @@ error_kobj:
error_cookie_jar:
fscache_proc_cleanup();
error_proc:
+ destroy_workqueue(fscache_op_wq);
+error_op_wq:
destroy_workqueue(fscache_object_wq);
error_object_wq:
slow_work_unregister_user(THIS_MODULE);
@@ -106,6 +114,7 @@ static void __exit fscache_exit(void)
kobject_put(fscache_root);
kmem_cache_destroy(fscache_cookie_jar);
fscache_proc_cleanup();
+ destroy_workqueue(fscache_op_wq);
destroy_workqueue(fscache_object_wq);
slow_work_unregister_user(THIS_MODULE);
printk(KERN_NOTICE "FS-Cache: Unloaded\n");
diff --git a/fs/fscache/operation.c b/fs/fscache/operation.c
index 313e79a..c673b32 100644
--- a/fs/fscache/operation.c
+++ b/fs/fscache/operation.c
@@ -41,16 +41,12 @@ void fscache_enqueue_operation(struct fscache_operation *op)

fscache_stat(&fscache_n_op_enqueue);
switch (op->flags & FSCACHE_OP_TYPE) {
- case FSCACHE_OP_FAST:
- _debug("queue fast");
+ case FSCACHE_OP_ASYNC:
+ _debug("queue async");
atomic_inc(&op->usage);
- if (!schedule_work(&op->fast_work))
+ if (!queue_work(fscache_op_wq, &op->work))
fscache_put_operation(op);
break;
- case FSCACHE_OP_SLOW:
- _debug("queue slow");
- slow_work_enqueue(&op->slow_work);
- break;
case FSCACHE_OP_MYTHREAD:
_debug("queue for caller's attention");
break;
@@ -454,36 +450,13 @@ void fscache_operation_gc(struct work_struct *work)
}

/*
- * allow the slow work item processor to get a ref on an operation
- */
-static int fscache_op_get_ref(struct slow_work *work)
-{
- struct fscache_operation *op =
- container_of(work, struct fscache_operation, slow_work);
-
- atomic_inc(&op->usage);
- return 0;
-}
-
-/*
- * allow the slow work item processor to discard a ref on an operation
- */
-static void fscache_op_put_ref(struct slow_work *work)
-{
- struct fscache_operation *op =
- container_of(work, struct fscache_operation, slow_work);
-
- fscache_put_operation(op);
-}
-
-/*
- * execute an operation using the slow thread pool to provide processing context
- * - the caller holds a ref to this object, so we don't need to hold one
+ * execute an operation using fs_op_wq to provide processing context -
+ * the caller holds a ref to this object, so we don't need to hold one
*/
-static void fscache_op_execute(struct slow_work *work)
+void fscache_op_work_func(struct work_struct *work)
{
struct fscache_operation *op =
- container_of(work, struct fscache_operation, slow_work);
+ container_of(work, struct fscache_operation, work);
unsigned long start;

_enter("{OBJ%x OP%x,%d}",
@@ -493,31 +466,7 @@ static void fscache_op_execute(struct slow_work *work)
start = jiffies;
op->processor(op);
fscache_hist(fscache_ops_histogram, start);
+ fscache_put_operation(op);

_leave("");
}
-
-/*
- * describe an operation for slow-work debugging
- */
-#ifdef CONFIG_SLOW_WORK_PROC
-static void fscache_op_desc(struct slow_work *work, struct seq_file *m)
-{
- struct fscache_operation *op =
- container_of(work, struct fscache_operation, slow_work);
-
- seq_printf(m, "FSC: OBJ%x OP%x: %s/%s fl=%lx",
- op->object->debug_id, op->debug_id,
- op->name, op->state, op->flags);
-}
-#endif
-
-const struct slow_work_ops fscache_op_slow_work_ops = {
- .owner = THIS_MODULE,
- .get_ref = fscache_op_get_ref,
- .put_ref = fscache_op_put_ref,
- .execute = fscache_op_execute,
-#ifdef CONFIG_SLOW_WORK_PROC
- .desc = fscache_op_desc,
-#endif
-};
diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index c598ea4..3d02944 100644
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -104,7 +104,7 @@ bool __fscache_maybe_release_page(struct fscache_cookie *cookie,

page_busy:
/* we might want to wait here, but that could deadlock the allocator as
- * the slow-work threads writing to the cache may all end up sleeping
+ * the work threads writing to the cache may all end up sleeping
* on memory allocation */
fscache_stat(&fscache_n_store_vmscan_busy);
return false;
@@ -187,9 +187,8 @@ int __fscache_attr_changed(struct fscache_cookie *cookie)
return -ENOMEM;
}

- fscache_operation_init(op, NULL);
- fscache_operation_init_slow(op, fscache_attr_changed_op);
- op->flags = FSCACHE_OP_SLOW | (1 << FSCACHE_OP_EXCLUSIVE);
+ fscache_operation_init(op, fscache_attr_changed_op, NULL);
+ op->flags = FSCACHE_OP_ASYNC | (1 << FSCACHE_OP_EXCLUSIVE);
fscache_set_op_name(op, "Attr");

spin_lock(&cookie->lock);
@@ -217,24 +216,6 @@ nobufs:
EXPORT_SYMBOL(__fscache_attr_changed);

/*
- * handle secondary execution given to a retrieval op on behalf of the
- * cache
- */
-static void fscache_retrieval_work(struct work_struct *work)
-{
- struct fscache_retrieval *op =
- container_of(work, struct fscache_retrieval, op.fast_work);
- unsigned long start;
-
- _enter("{OP%x}", op->op.debug_id);
-
- start = jiffies;
- op->op.processor(&op->op);
- fscache_hist(fscache_ops_histogram, start);
- fscache_put_operation(&op->op);
-}
-
-/*
* release a retrieval op reference
*/
static void fscache_release_retrieval_op(struct fscache_operation *_op)
@@ -268,13 +249,12 @@ static struct fscache_retrieval *fscache_alloc_retrieval(
return NULL;
}

- fscache_operation_init(&op->op, fscache_release_retrieval_op);
+ fscache_operation_init(&op->op, NULL, fscache_release_retrieval_op);
op->op.flags = FSCACHE_OP_MYTHREAD | (1 << FSCACHE_OP_WAITING);
op->mapping = mapping;
op->end_io_func = end_io_func;
op->context = context;
op->start_time = jiffies;
- INIT_WORK(&op->op.fast_work, fscache_retrieval_work);
INIT_LIST_HEAD(&op->to_do);
fscache_set_op_name(&op->op, "Retr");
return op;
@@ -798,9 +778,9 @@ int __fscache_write_page(struct fscache_cookie *cookie,
if (!op)
goto nomem;

- fscache_operation_init(&op->op, fscache_release_write_op);
- fscache_operation_init_slow(&op->op, fscache_write_op);
- op->op.flags = FSCACHE_OP_SLOW | (1 << FSCACHE_OP_WAITING);
+ fscache_operation_init(&op->op, fscache_write_op,
+ fscache_release_write_op);
+ op->op.flags = FSCACHE_OP_ASYNC | (1 << FSCACHE_OP_WAITING);
fscache_set_op_name(&op->op, "Write1");

ret = radix_tree_preload(gfp & ~__GFP_HIGHMEM);
@@ -855,7 +835,7 @@ int __fscache_write_page(struct fscache_cookie *cookie,
fscache_stat(&fscache_n_store_ops);
fscache_stat(&fscache_n_stores_ok);

- /* the slow work queue now carries its own ref on the object */
+ /* the work queue now carries its own ref on the object */
fscache_put_operation(&op->op);
_leave(" = 0");
return 0;
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 63b7f76..7791f2c 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -77,18 +77,14 @@ typedef void (*fscache_operation_release_t)(struct fscache_operation *op);
typedef void (*fscache_operation_processor_t)(struct fscache_operation *op);

struct fscache_operation {
- union {
- struct work_struct fast_work; /* record for fast ops */
- struct slow_work slow_work; /* record for (very) slow ops */
- };
+ struct work_struct work; /* record for async ops */
struct list_head pend_link; /* link in object->pending_ops */
struct fscache_object *object; /* object to be operated upon */

unsigned long flags;
#define FSCACHE_OP_TYPE 0x000f /* operation type */
-#define FSCACHE_OP_FAST 0x0001 /* - fast op, processor may not sleep for disk */
-#define FSCACHE_OP_SLOW 0x0002 /* - (very) slow op, processor may sleep for disk */
-#define FSCACHE_OP_MYTHREAD 0x0003 /* - processing is done be issuing thread, not pool */
+#define FSCACHE_OP_ASYNC 0x0001 /* - async op, processor may sleep for disk */
+#define FSCACHE_OP_MYTHREAD 0x0002 /* - processing is done be issuing thread, not pool */
#define FSCACHE_OP_WAITING 4 /* cleared when op is woken */
#define FSCACHE_OP_EXCLUSIVE 5 /* exclusive op, other ops must wait */
#define FSCACHE_OP_DEAD 6 /* op is now dead */
@@ -118,7 +114,7 @@ struct fscache_operation {
};

extern atomic_t fscache_op_debug_id;
-extern const struct slow_work_ops fscache_op_slow_work_ops;
+extern void fscache_op_work_func(struct work_struct *work);

extern void fscache_enqueue_operation(struct fscache_operation *);
extern void fscache_put_operation(struct fscache_operation *);
@@ -129,33 +125,21 @@ extern void fscache_put_operation(struct fscache_operation *);
* @release: The release function to assign
*
* Do basic initialisation of an operation. The caller must still set flags,
- * object, either fast_work or slow_work if necessary, and processor if needed.
+ * object and processor if needed.
*/
static inline void fscache_operation_init(struct fscache_operation *op,
- fscache_operation_release_t release)
+ fscache_operation_processor_t processor,
+ fscache_operation_release_t release)
{
+ INIT_WORK(&op->work, fscache_op_work_func);
atomic_set(&op->usage, 1);
op->debug_id = atomic_inc_return(&fscache_op_debug_id);
+ op->processor = processor;
op->release = release;
INIT_LIST_HEAD(&op->pend_link);
fscache_set_op_state(op, "Init");
}

-/**
- * fscache_operation_init_slow - Do additional initialisation of a slow op
- * @op: The operation to initialise
- * @processor: The processor function to assign
- *
- * Do additional initialisation of an operation as required for slow work.
- */
-static inline
-void fscache_operation_init_slow(struct fscache_operation *op,
- fscache_operation_processor_t processor)
-{
- op->processor = processor;
- slow_work_init(&op->slow_work, &fscache_op_slow_work_ops);
-}
-
/*
* data read operation
*/
--
1.6.4.2