[PATCH 1/7] fscache: convert object to use workqueue instead of slow-work

From: Tejun Heo
Date: Tue Jul 20 2010 - 16:36:53 EST

Make fscache object state transition callbacks use workqueue instead
of slow-work. New dedicated unbound CPU workqueue fscache_object_wq
is created. get/put callbacks are renamed and modified to take
@object and called directly from the enqueue wrapper and the work
function. While at it, make all open coded instances of get/put to
use fscache_get/put_object().

* Unbound workqueue is used.

* work_busy() output is printed instead of slow-work flags in object
debugging outputs. They mean basically the same thing bit-for-bit.

* sysctl fscache.object_max_active added to control concurrency. The
default value is nr_cpus clamped between 4 and
WQ_UNBOUND_MAX_ACTIVE.

* slow_work_sleep_till_thread_needed() is replaced with fscache
private implementation fscache_object_sleep_till_congested() which
waits on fscache_object_wq congestion.

* debugfs support is dropped for now. Tracing API based debug
facility is planned to be added.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
---
Documentation/filesystems/caching/fscache.txt | 10 +-
fs/cachefiles/namei.c | 13 ++--
fs/fscache/internal.h | 7 ++
fs/fscache/main.c | 76 ++++++++++++++++++
fs/fscache/object-list.c | 11 +--
fs/fscache/object.c | 106 ++++++++++++------------
include/linux/fscache-cache.h | 9 ++-
7 files changed, 158 insertions(+), 74 deletions(-)

diff --git a/Documentation/filesystems/caching/fscache.txt b/Documentation/filesystems/caching/fscache.txt
index a91e2e2..770267a 100644
--- a/Documentation/filesystems/caching/fscache.txt
+++ b/Documentation/filesystems/caching/fscache.txt
@@ -343,8 +343,8 @@ This will look something like:
[root@andromeda ~]# head /proc/fs/fscache/objects
OBJECT PARENT STAT CHLDN OPS OOP IPR EX READS EM EV F S | NETFS_COOKIE_DEF TY FL NETFS_DATA OBJECT_KEY, AUX_DATA
======== ======== ==== ===== === === === == ===== == == = = | ================ == == ================ ================
- 17e4b 2 ACTV 0 0 0 0 0 0 7b 4 0 8 | NFS.fh DT 0 ffff88001dd82820 010006017edcf8bbc93b43298fdfbe71e50b57b13a172c0117f38472, e567634700000000000000000000000063f2404a000000000000000000000000c9030000000000000000000063f2404a
- 1693a 2 ACTV 0 0 0 0 0 0 7b 4 0 8 | NFS.fh DT 0 ffff88002db23380 010006017edcf8bbc93b43298fdfbe71e50b57b1e0162c01a2df0ea6, 420ebc4a000000000000000000000000420ebc4a0000000000000000000000000e1801000000000000000000420ebc4a
+ 17e4b 2 ACTV 0 0 0 0 0 0 7b 4 0 0 | NFS.fh DT 0 ffff88001dd82820 010006017edcf8bbc93b43298fdfbe71e50b57b13a172c0117f38472, e567634700000000000000000000000063f2404a000000000000000000000000c9030000000000000000000063f2404a
+ 1693a 2 ACTV 0 0 0 0 0 0 7b 4 0 0 | NFS.fh DT 0 ffff88002db23380 010006017edcf8bbc93b43298fdfbe71e50b57b1e0162c01a2df0ea6, 420ebc4a000000000000000000000000420ebc4a0000000000000000000000000e1801000000000000000000420ebc4a

where the first set of columns before the '|' describe the object:

@@ -362,7 +362,7 @@ where the first set of columns before the '|' describe the object:
EM Object's event mask
EV Events raised on this object
F Object flags
- S Object slow-work work item flags
+ S Object work item busy state mask (1:pending 2:running)

and the second set of columns describe the object's cookie, if present:

@@ -395,8 +395,8 @@ and the following paired letters:
w Show objects that don't have pending writes
R Show objects that have outstanding reads
r Show objects that don't have outstanding reads
- S Show objects that have slow work queued
- s Show objects that don't have slow work queued
+ S Show objects that have work queued
+ s Show objects that don't have work queued

If neither side of a letter pair is given, then both are implied. For example:

diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index f4a7840..42c7faf 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -37,9 +37,9 @@ void __cachefiles_printk_object(struct cachefiles_object *object,

printk(KERN_ERR "%sobject: OBJ%x\n",
prefix, object->fscache.debug_id);
- printk(KERN_ERR "%sobjstate=%s fl=%lx swfl=%lx ev=%lx[%lx]\n",
+ printk(KERN_ERR "%sobjstate=%s fl=%lx wbusy=%x ev=%lx[%lx]\n",
prefix, fscache_object_states[object->fscache.state],
- object->fscache.flags, object->fscache.work.flags,
+ object->fscache.flags, work_busy(&object->fscache.work),
object->fscache.events,
object->fscache.event_mask & FSCACHE_OBJECT_EVENTS_MASK);
printk(KERN_ERR "%sops=%u inp=%u exc=%u\n",
@@ -212,7 +212,7 @@ wait_for_old_object:

/* if the object we're waiting for is queued for processing,
* then just put ourselves on the queue behind it */
- if (slow_work_is_queued(&xobject->fscache.work)) {
+ if (work_pending(&xobject->fscache.work)) {
_debug("queue OBJ%x behind OBJ%x immediately",
object->fscache.debug_id,
xobject->fscache.debug_id);
@@ -220,8 +220,7 @@ wait_for_old_object:
}

/* otherwise we sleep until either the object we're waiting for
- * is done, or the slow-work facility wants the thread back to
- * do other work */
+ * is done, or the fscache_object is congested */
wq = bit_waitqueue(&xobject->flags, CACHEFILES_OBJECT_ACTIVE);
init_wait(&wait);
requeue = false;
@@ -229,8 +228,8 @@ wait_for_old_object:
prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
if (!test_bit(CACHEFILES_OBJECT_ACTIVE, &xobject->flags))
break;
- requeue = slow_work_sleep_till_thread_needed(
- &object->fscache.work, &timeout);
+
+ requeue = fscache_object_sleep_till_congested(&timeout);
} while (timeout > 0 && !requeue);
finish_wait(wq, &wait);

diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index edd7434..6e0b5fb 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -82,6 +82,13 @@ extern unsigned fscache_defer_lookup;
extern unsigned fscache_defer_create;
extern unsigned fscache_debug;
extern struct kobject *fscache_root;
+extern struct workqueue_struct *fscache_object_wq;
+DECLARE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait);
+
+static inline bool fscache_object_congested(void)
+{
+ return workqueue_congested(WORK_CPU_UNBOUND, fscache_object_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 add6bdb..bb8d4c3 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -15,6 +15,7 @@
#include <linux/sched.h>
#include <linux/completion.h>
#include <linux/slab.h>
+#include <linux/seq_file.h>
#include "internal.h"

MODULE_DESCRIPTION("FS Cache Manager");
@@ -40,22 +41,89 @@ MODULE_PARM_DESC(fscache_debug,
"FS-Cache debugging mask");

struct kobject *fscache_root;
+struct workqueue_struct *fscache_object_wq;
+
+DEFINE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait);
+
+/* these values serve as lower bounds, will be adjusted in fscache_init() */
+static unsigned fscache_object_max_active = 4;
+
+#ifdef CONFIG_SYSCTL
+static struct ctl_table_header *fscache_sysctl_header;
+
+static int fscache_max_active_sysctl(struct ctl_table *table, int write,
+ void __user *buffer,
+ size_t *lenp, loff_t *ppos)
+{
+ struct workqueue_struct **wqp = table->extra1;
+ unsigned int *datap = table->data;
+ int ret;
+
+ ret = proc_dointvec(table, write, buffer, lenp, ppos);
+ if (ret == 0)
+ workqueue_set_max_active(*wqp, *datap);
+ return ret;
+}
+
+ctl_table fscache_sysctls[] = {
+ {
+ .procname = "object_max_active",
+ .data = &fscache_object_max_active,
+ .maxlen = sizeof(unsigned),
+ .mode = 0644,
+ .proc_handler = fscache_max_active_sysctl,
+ .extra1 = &fscache_object_wq,
+ },
+ {}
+};
+
+ctl_table fscache_sysctls_root[] = {
+ {
+ .procname = "fscache",
+ .mode = 0555,
+ .child = fscache_sysctls,
+ },
+ {}
+};
+#endif

/*
* initialise the fs caching module
*/
static int __init fscache_init(void)
{
+ unsigned int nr_cpus = num_possible_cpus();
+ unsigned int cpu;
int ret;

ret = slow_work_register_user(THIS_MODULE);
if (ret < 0)
goto error_slow_work;

+ fscache_object_max_active =
+ clamp_val(nr_cpus,
+ fscache_object_max_active, WQ_UNBOUND_MAX_ACTIVE);
+
+ ret = -ENOMEM;
+ fscache_object_wq = alloc_workqueue("fscache_object", WQ_UNBOUND,
+ fscache_object_max_active);
+ if (!fscache_object_wq)
+ goto error_object_wq;
+
+ for_each_possible_cpu(cpu)
+ init_waitqueue_head(&per_cpu(fscache_object_cong_wait, cpu));
+
ret = fscache_proc_init();
if (ret < 0)
goto error_proc;

+#ifdef CONFIG_SYSCTL
+ ret = -ENOMEM;
+ fscache_sysctl_header = register_sysctl_table(fscache_sysctls_root);
+ if (!fscache_sysctl_header)
+ goto error_sysctl;
+#endif
+
fscache_cookie_jar = kmem_cache_create("fscache_cookie_jar",
sizeof(struct fscache_cookie),
0,
@@ -78,8 +146,14 @@ static int __init fscache_init(void)
error_kobj:
kmem_cache_destroy(fscache_cookie_jar);
error_cookie_jar:
+#ifdef CONFIG_SYSCTL
+ unregister_sysctl_table(fscache_sysctl_header);
+error_sysctl:
+#endif
fscache_proc_cleanup();
error_proc:
+ destroy_workqueue(fscache_object_wq);
+error_object_wq:
slow_work_unregister_user(THIS_MODULE);
error_slow_work:
return ret;
@@ -96,7 +170,9 @@ static void __exit fscache_exit(void)

kobject_put(fscache_root);
kmem_cache_destroy(fscache_cookie_jar);
+ unregister_sysctl_table(fscache_sysctl_header);
fscache_proc_cleanup();
+ destroy_workqueue(fscache_object_wq);
slow_work_unregister_user(THIS_MODULE);
printk(KERN_NOTICE "FS-Cache: Unloaded\n");
}
diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c
index 4a8eb31..ebe29c5 100644
--- a/fs/fscache/object-list.c
+++ b/fs/fscache/object-list.c
@@ -34,8 +34,8 @@ struct fscache_objlist_data {
#define FSCACHE_OBJLIST_CONFIG_NOREADS 0x00000200 /* show objects without active reads */
#define FSCACHE_OBJLIST_CONFIG_EVENTS 0x00000400 /* show objects with events */
#define FSCACHE_OBJLIST_CONFIG_NOEVENTS 0x00000800 /* show objects without no events */
-#define FSCACHE_OBJLIST_CONFIG_WORK 0x00001000 /* show objects with slow work */
-#define FSCACHE_OBJLIST_CONFIG_NOWORK 0x00002000 /* show objects without slow work */
+#define FSCACHE_OBJLIST_CONFIG_WORK 0x00001000 /* show objects with work */
+#define FSCACHE_OBJLIST_CONFIG_NOWORK 0x00002000 /* show objects without work */

u8 buf[512]; /* key and aux data buffer */
};
@@ -231,12 +231,11 @@ static int fscache_objlist_show(struct seq_file *m, void *v)
READS, NOREADS);
FILTER(obj->events & obj->event_mask,
EVENTS, NOEVENTS);
- FILTER(obj->work.flags & ~(1UL << SLOW_WORK_VERY_SLOW),
- WORK, NOWORK);
+ FILTER(work_busy(&obj->work), WORK, NOWORK);
}

seq_printf(m,
- "%8x %8x %s %5u %3u %3u %3u %2u %5u %2lx %2lx %1lx %1lx | ",
+ "%8x %8x %s %5u %3u %3u %3u %2u %5u %2lx %2lx %1lx %1x | ",
obj->debug_id,
obj->parent ? obj->parent->debug_id : -1,
fscache_object_states_short[obj->state],
@@ -249,7 +248,7 @@ static int fscache_objlist_show(struct seq_file *m, void *v)
obj->event_mask & FSCACHE_OBJECT_EVENTS_MASK,
obj->events,
obj->flags,
- obj->work.flags);
+ work_busy(&obj->work));

no_cookie = true;
keylen = auxlen = 0;
diff --git a/fs/fscache/object.c b/fs/fscache/object.c
index 0b589a9..b6b897c 100644
--- a/fs/fscache/object.c
+++ b/fs/fscache/object.c
@@ -14,7 +14,6 @@

#define FSCACHE_DEBUG_LEVEL COOKIE
#include <linux/module.h>
-#include <linux/seq_file.h>
#include "internal.h"

const char *fscache_object_states[FSCACHE_OBJECT__NSTATES] = {
@@ -50,12 +49,8 @@ const char fscache_object_states_short[FSCACHE_OBJECT__NSTATES][5] = {
[FSCACHE_OBJECT_DEAD] = "DEAD",
};

-static void fscache_object_slow_work_put_ref(struct slow_work *);
-static int fscache_object_slow_work_get_ref(struct slow_work *);
-static void fscache_object_slow_work_execute(struct slow_work *);
-#ifdef CONFIG_SLOW_WORK_DEBUG
-static void fscache_object_slow_work_desc(struct slow_work *, struct seq_file *);
-#endif
+static int fscache_get_object(struct fscache_object *);
+static void fscache_put_object(struct fscache_object *);
static void fscache_initialise_object(struct fscache_object *);
static void fscache_lookup_object(struct fscache_object *);
static void fscache_object_available(struct fscache_object *);
@@ -64,17 +59,6 @@ static void fscache_withdraw_object(struct fscache_object *);
static void fscache_enqueue_dependents(struct fscache_object *);
static void fscache_dequeue_object(struct fscache_object *);

-const struct slow_work_ops fscache_object_slow_work_ops = {
- .owner = THIS_MODULE,
- .get_ref = fscache_object_slow_work_get_ref,
- .put_ref = fscache_object_slow_work_put_ref,
- .execute = fscache_object_slow_work_execute,
-#ifdef CONFIG_SLOW_WORK_DEBUG
- .desc = fscache_object_slow_work_desc,
-#endif
-};
-EXPORT_SYMBOL(fscache_object_slow_work_ops);
-
/*
* we need to notify the parent when an op completes that we had outstanding
* upon it
@@ -345,7 +329,7 @@ unsupported_event:
/*
* execute an object
*/
-static void fscache_object_slow_work_execute(struct slow_work *work)
+void fscache_object_work_func(struct work_struct *work)
{
struct fscache_object *object =
container_of(work, struct fscache_object, work);
@@ -359,23 +343,9 @@ static void fscache_object_slow_work_execute(struct slow_work *work)
if (object->events & object->event_mask)
fscache_enqueue_object(object);
clear_bit(FSCACHE_OBJECT_EV_REQUEUE, &object->events);
+ fscache_put_object(object);
}
-
-/*
- * describe an object for slow-work debugging
- */
-#ifdef CONFIG_SLOW_WORK_DEBUG
-static void fscache_object_slow_work_desc(struct slow_work *work,
- struct seq_file *m)
-{
- struct fscache_object *object =
- container_of(work, struct fscache_object, work);
-
- seq_printf(m, "FSC: OBJ%x: %s",
- object->debug_id,
- fscache_object_states_short[object->state]);
-}
-#endif
+EXPORT_SYMBOL(fscache_object_work_func);

/*
* initialise an object
@@ -393,7 +363,6 @@ static void fscache_initialise_object(struct fscache_object *object)
_enter("");
ASSERT(object->cookie != NULL);
ASSERT(object->cookie->parent != NULL);
- ASSERT(list_empty(&object->work.link));

if (object->events & ((1 << FSCACHE_OBJECT_EV_ERROR) |
(1 << FSCACHE_OBJECT_EV_RELEASE) |
@@ -671,10 +640,8 @@ static void fscache_drop_object(struct fscache_object *object)
object->parent = NULL;
}

- /* this just shifts the object release to the slow work processor */
- fscache_stat(&fscache_n_cop_put_object);
- object->cache->ops->put_object(object);
- fscache_stat_d(&fscache_n_cop_put_object);
+ /* this just shifts the object release to the work processor */
+ fscache_put_object(object);

_leave("");
}
@@ -758,12 +725,10 @@ void fscache_withdrawing_object(struct fscache_cache *cache,
}

/*
- * allow the slow work item processor to get a ref on an object
+ * get a ref on an object
*/
-static int fscache_object_slow_work_get_ref(struct slow_work *work)
+static int fscache_get_object(struct fscache_object *object)
{
- struct fscache_object *object =
- container_of(work, struct fscache_object, work);
int ret;

fscache_stat(&fscache_n_cop_grab_object);
@@ -773,13 +738,10 @@ static int fscache_object_slow_work_get_ref(struct slow_work *work)
}

/*
- * allow the slow work item processor to discard a ref on a work item
+ * discard a ref on a work item
*/
-static void fscache_object_slow_work_put_ref(struct slow_work *work)
+static void fscache_put_object(struct fscache_object *object)
{
- struct fscache_object *object =
- container_of(work, struct fscache_object, work);
-
fscache_stat(&fscache_n_cop_put_object);
object->cache->ops->put_object(object);
fscache_stat_d(&fscache_n_cop_put_object);
@@ -792,8 +754,48 @@ void fscache_enqueue_object(struct fscache_object *object)
{
_enter("{OBJ%x}", object->debug_id);

- slow_work_enqueue(&object->work);
+ if (fscache_get_object(object) >= 0) {
+ wait_queue_head_t *cong_wq =
+ &get_cpu_var(fscache_object_cong_wait);
+
+ if (queue_work(fscache_object_wq, &object->work)) {
+ if (fscache_object_congested())
+ wake_up(cong_wq);
+ } else
+ fscache_put_object(object);
+
+ put_cpu_var(fscache_object_cong_wait);
+ }
+}
+
+/**
+ * fscache_object_sleep_till_congested - Sleep until object wq is congested
+ * @timoutp: Scheduler sleep timeout
+ *
+ * Allow an object handler to sleep until the object workqueue is congested.
+ *
+ * The caller must set up a wake up event before calling this and must have set
+ * the appropriate sleep mode (such as TASK_UNINTERRUPTIBLE) and tested its own
+ * condition before calling this function as no test is made here.
+ *
+ * %true is returned if the object wq is congested, %false otherwise.
+ */
+bool fscache_object_sleep_till_congested(signed long *timeoutp)
+{
+ wait_queue_head_t *cong_wq = &__get_cpu_var(fscache_object_cong_wait);
+ DEFINE_WAIT(wait);
+
+ if (fscache_object_congested())
+ return true;
+
+ add_wait_queue_exclusive(cong_wq, &wait);
+ if (!fscache_object_congested())
+ *timeoutp = schedule_timeout(*timeoutp);
+ finish_wait(cong_wq, &wait);
+
+ return fscache_object_congested();
}
+EXPORT_SYMBOL_GPL(fscache_object_sleep_till_congested);

/*
* enqueue the dependents of an object for metadata-type processing
@@ -819,9 +821,7 @@ static void fscache_enqueue_dependents(struct fscache_object *object)

/* sort onto appropriate lists */
fscache_enqueue_object(dep);
- fscache_stat(&fscache_n_cop_put_object);
- dep->cache->ops->put_object(dep);
- fscache_stat_d(&fscache_n_cop_put_object);
+ fscache_put_object(dep);

if (!list_empty(&object->dependents))
cond_resched_lock(&object->lock);
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index c57db27..27c8df5 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -21,6 +21,7 @@
#include <linux/fscache.h>
#include <linux/sched.h>
#include <linux/slow-work.h>
+#include <linux/workqueue.h>

#define NR_MAXCACHES BITS_PER_LONG

@@ -389,7 +390,7 @@ struct fscache_object {
struct fscache_cache *cache; /* cache that supplied this object */
struct fscache_cookie *cookie; /* netfs's file/index object */
struct fscache_object *parent; /* parent object */
- struct slow_work work; /* attention scheduling record */
+ struct work_struct work; /* attention scheduling record */
struct list_head dependents; /* FIFO of dependent objects */
struct list_head dep_link; /* link in parent's dependents list */
struct list_head pending_ops; /* unstarted operations on this object */
@@ -411,7 +412,7 @@ extern const char *fscache_object_states[];
(test_bit(FSCACHE_IOERROR, &(obj)->cache->flags) && \
(obj)->state >= FSCACHE_OBJECT_DYING)

-extern const struct slow_work_ops fscache_object_slow_work_ops;
+extern void fscache_object_work_func(struct work_struct *work);

/**
* fscache_object_init - Initialise a cache object description
@@ -433,7 +434,7 @@ void fscache_object_init(struct fscache_object *object,
spin_lock_init(&object->lock);
INIT_LIST_HEAD(&object->cache_link);
INIT_HLIST_NODE(&object->cookie_link);
- vslow_work_init(&object->work, &fscache_object_slow_work_ops);
+ INIT_WORK(&object->work, fscache_object_work_func);
INIT_LIST_HEAD(&object->dependents);
INIT_LIST_HEAD(&object->dep_link);
INIT_LIST_HEAD(&object->pending_ops);
@@ -534,6 +535,8 @@ extern void fscache_io_error(struct fscache_cache *cache);
extern void fscache_mark_pages_cached(struct fscache_retrieval *op,
struct pagevec *pagevec);

+extern bool fscache_object_sleep_till_congested(signed long *timeoutp);
+
extern enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
const void *data,
uint16_t datalen);
--
1.6.4.2

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