dm cache: significant rework to leverage dm-bio-prison-v2

The cache policy interfaces have been updated to work well with the new
bio-prison v2 interface's ability to queue work immediately (promotion,
demotion, etc) -- overriding benefit being reduced latency on processing
IO through the cache.  Previously such work would be left for the DM
cache core to queue on various lists and then process in batches later
-- this caused a serious delay in latency for IO driven by the cache.

The background tracker code was factored out so that all cache policies
can make use of it.

Also, the "cleaner" policy has been removed and is now a variant of the
smq policy that simply disallows migrations.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/Kconfig

@@ -325,14 +325,6 @@ config DM_CACHE_SMQ
          of less memory utilization, improved performance and increased
          adaptability in the face of changing workloads.
 
-config DM_CACHE_CLEANER
-       tristate "Cleaner Cache Policy (EXPERIMENTAL)"
-       depends on DM_CACHE
-       default y
-       ---help---
-         A simple cache policy that writes back all data to the
-         origin.  Used when decommissioning a dm-cache.
-
 config DM_ERA
        tristate "Era target (EXPERIMENTAL)"
        depends on BLK_DEV_DM

drivers/md/Makefile

@@ -13,9 +13,9 @@ dm-log-userspace-y \
 		+= dm-log-userspace-base.o dm-log-userspace-transfer.o
 dm-bio-prison-y += dm-bio-prison-v1.o dm-bio-prison-v2.o
 dm-thin-pool-y	+= dm-thin.o dm-thin-metadata.o
-dm-cache-y	+= dm-cache-target.o dm-cache-metadata.o dm-cache-policy.o
+dm-cache-y	+= dm-cache-target.o dm-cache-metadata.o dm-cache-policy.o \
+		    dm-cache-background-tracker.o
 dm-cache-smq-y   += dm-cache-policy-smq.o
-dm-cache-cleaner-y += dm-cache-policy-cleaner.o
 dm-era-y	+= dm-era-target.o
 dm-verity-y	+= dm-verity-target.o
 md-mod-y	+= md.o bitmap.o
@@ -57,7 +57,6 @@ obj-$(CONFIG_DM_THIN_PROVISIONING)	+= dm-thin-pool.o
 obj-$(CONFIG_DM_VERITY)		+= dm-verity.o
 obj-$(CONFIG_DM_CACHE)		+= dm-cache.o
 obj-$(CONFIG_DM_CACHE_SMQ)	+= dm-cache-smq.o
-obj-$(CONFIG_DM_CACHE_CLEANER)	+= dm-cache-cleaner.o
 obj-$(CONFIG_DM_ERA)		+= dm-era.o
 obj-$(CONFIG_DM_LOG_WRITES)	+= dm-log-writes.o
 

drivers/md/dm-cache-background-tracker.c

@@ -0,0 +1,238 @@
+/*
+ * Copyright (C) 2017 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-cache-background-tracker.h"
+
+/*----------------------------------------------------------------*/
+
+#define DM_MSG_PREFIX "dm-background-tracker"
+
+struct bt_work {
+	struct list_head list;
+	struct rb_node node;
+	struct policy_work work;
+};
+
+struct background_tracker {
+	unsigned max_work;
+	atomic_t pending_promotes;
+	atomic_t pending_writebacks;
+	atomic_t pending_demotes;
+
+	struct list_head issued;
+	struct list_head queued;
+	struct rb_root pending;
+
+	struct kmem_cache *work_cache;
+};
+
+struct background_tracker *btracker_create(unsigned max_work)
+{
+	struct background_tracker *b = kmalloc(sizeof(*b), GFP_KERNEL);
+
+	b->max_work = max_work;
+	atomic_set(&b->pending_promotes, 0);
+	atomic_set(&b->pending_writebacks, 0);
+	atomic_set(&b->pending_demotes, 0);
+
+	INIT_LIST_HEAD(&b->issued);
+	INIT_LIST_HEAD(&b->queued);
+
+	b->pending = RB_ROOT;
+	b->work_cache = KMEM_CACHE(bt_work, 0);
+	if (!b->work_cache) {
+		DMERR("couldn't create mempool for background work items");
+		kfree(b);
+		b = NULL;
+	}
+
+	return b;
+}
+EXPORT_SYMBOL_GPL(btracker_create);
+
+void btracker_destroy(struct background_tracker *b)
+{
+	kmem_cache_destroy(b->work_cache);
+	kfree(b);
+}
+EXPORT_SYMBOL_GPL(btracker_destroy);
+
+static int cmp_oblock(dm_oblock_t lhs, dm_oblock_t rhs)
+{
+	if (from_oblock(lhs) < from_oblock(rhs))
+		return -1;
+
+	if (from_oblock(rhs) < from_oblock(lhs))
+		return 1;
+
+	return 0;
+}
+
+static bool __insert_pending(struct background_tracker *b,
+			     struct bt_work *nw)
+{
+	int cmp;
+	struct bt_work *w;
+	struct rb_node **new = &b->pending.rb_node, *parent = NULL;
+
+	while (*new) {
+		w = container_of(*new, struct bt_work, node);
+
+		parent = *new;
+		cmp = cmp_oblock(w->work.oblock, nw->work.oblock);
+		if (cmp < 0)
+			new = &((*new)->rb_left);
+
+		else if (cmp > 0)
+			new = &((*new)->rb_right);
+
+		else
+			/* already present */
+			return false;
+	}
+
+	rb_link_node(&nw->node, parent, new);
+	rb_insert_color(&nw->node, &b->pending);
+
+	return true;
+}
+
+static struct bt_work *__find_pending(struct background_tracker *b,
+				      dm_oblock_t oblock)
+{
+	int cmp;
+	struct bt_work *w;
+	struct rb_node **new = &b->pending.rb_node;
+
+	while (*new) {
+		w = container_of(*new, struct bt_work, node);
+
+		cmp = cmp_oblock(w->work.oblock, oblock);
+		if (cmp < 0)
+			new = &((*new)->rb_left);
+
+		else if (cmp > 0)
+			new = &((*new)->rb_right);
+
+		else
+			break;
+	}
+
+	return *new ? w : NULL;
+}
+
+
+static void update_stats(struct background_tracker *b, struct policy_work *w, int delta)
+{
+	switch (w->op) {
+	case POLICY_PROMOTE:
+		atomic_add(delta, &b->pending_promotes);
+		break;
+
+	case POLICY_DEMOTE:
+		atomic_add(delta, &b->pending_demotes);
+		break;
+
+	case POLICY_WRITEBACK:
+		atomic_add(delta, &b->pending_writebacks);
+		break;
+	}
+}
+
+unsigned btracker_nr_writebacks_queued(struct background_tracker *b)
+{
+	return atomic_read(&b->pending_writebacks);
+}
+EXPORT_SYMBOL_GPL(btracker_nr_writebacks_queued);
+
+unsigned btracker_nr_demotions_queued(struct background_tracker *b)
+{
+	return atomic_read(&b->pending_demotes);
+}
+EXPORT_SYMBOL_GPL(btracker_nr_demotions_queued);
+
+static bool max_work_reached(struct background_tracker *b)
+{
+	// FIXME: finish
+	return false;
+}
+
+int btracker_queue(struct background_tracker *b,
+		   struct policy_work *work,
+		   struct policy_work **pwork)
+{
+	struct bt_work *w;
+
+	if (pwork)
+		*pwork = NULL;
+
+	if (max_work_reached(b))
+		return -ENOMEM;
+
+	w = kmem_cache_alloc(b->work_cache, GFP_NOWAIT);
+	if (!w)
+		return -ENOMEM;
+
+	memcpy(&w->work, work, sizeof(*work));
+
+	if (!__insert_pending(b, w)) {
+		/*
+		 * There was a race, we'll just ignore this second
+		 * bit of work for the same oblock.
+		 */
+		kmem_cache_free(b->work_cache, w);
+		return -EINVAL;
+	}
+
+	if (pwork) {
+		*pwork = &w->work;
+		list_add(&w->list, &b->issued);
+	} else
+		list_add(&w->list, &b->queued);
+	update_stats(b, &w->work, 1);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(btracker_queue);
+
+/*
+ * Returns -ENODATA if there's no work.
+ */
+int btracker_issue(struct background_tracker *b, struct policy_work **work)
+{
+	struct bt_work *w;
+
+	if (list_empty(&b->queued))
+		return -ENODATA;
+
+	w = list_first_entry(&b->queued, struct bt_work, list);
+	list_move(&w->list, &b->issued);
+	*work = &w->work;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(btracker_issue);
+
+void btracker_complete(struct background_tracker *b,
+		       struct policy_work *op)
+{
+	struct bt_work *w = container_of(op, struct bt_work, work);
+
+	update_stats(b, &w->work, -1);
+	rb_erase(&w->node, &b->pending);
+	list_del(&w->list);
+	kmem_cache_free(b->work_cache, w);
+}
+EXPORT_SYMBOL_GPL(btracker_complete);
+
+bool btracker_promotion_already_present(struct background_tracker *b,
+					dm_oblock_t oblock)
+{
+	return __find_pending(b, oblock) != NULL;
+}
+EXPORT_SYMBOL_GPL(btracker_promotion_already_present);
+
+/*----------------------------------------------------------------*/

drivers/md/dm-cache-background-tracker.h

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2017 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_BACKGROUND_WORK_H
+#define DM_CACHE_BACKGROUND_WORK_H
+
+#include <linux/vmalloc.h>
+#include "dm-cache-policy.h"
+
+/*----------------------------------------------------------------*/
+
+struct background_work;
+struct background_tracker;
+
+/*
+ * FIXME: discuss lack of locking in all methods.
+ */
+struct background_tracker *btracker_create(unsigned max_work);
+void btracker_destroy(struct background_tracker *b);
+
+unsigned btracker_nr_writebacks_queued(struct background_tracker *b);
+unsigned btracker_nr_demotions_queued(struct background_tracker *b);
+
+/*
+ * returns -EINVAL iff the work is already queued.  -ENOMEM if the work
+ * couldn't be queued for another reason.
+ */
+int btracker_queue(struct background_tracker *b,
+		   struct policy_work *work,
+		   struct policy_work **pwork);
+
+/*
+ * Returns -ENODATA if there's no work.
+ */
+int btracker_issue(struct background_tracker *b, struct policy_work **work);
+void btracker_complete(struct background_tracker *b,
+		       struct policy_work *op);
+bool btracker_promotion_already_present(struct background_tracker *b,
+					dm_oblock_t oblock);
+
+/*----------------------------------------------------------------*/
+
+#endif

drivers/md/dm-cache-metadata.h

@@ -50,6 +50,8 @@
 #define DM_CACHE_FEATURE_COMPAT_RO_SUPP	  0UL
 #define DM_CACHE_FEATURE_INCOMPAT_SUPP	  0UL
 
+struct dm_cache_metadata;
+
 /*
  * Reopens or creates a new, empty metadata volume.  Returns an ERR_PTR on
  * failure.  If reopening then features must match.