[PATCH 22/49] writeback: make backing_dev_info host cgroup-specific bdi_writebacks

Tejun Heo
2015-04-06T20:17:40Z

For the planned cgroup writeback support, on each bdi
(backing_dev_info), each memcg will be served by a separate wb
(bdi_writeback). This patch updates bdi so that a bdi can host
multiple wbs (bdi_writebacks).

On the default hierarchy, blkcg implicitly enables memcg. This allows
using memcg's page ownership for attributing writeback IOs, and every
memcg - blkcg combination can be served by its own wb by assigning a
dedicated wb to each memcg. This means that there may be multiple
wb's of a bdi mapped to the same blkcg. As congested state is per
blkcg - bdi combination, those wb's should share the same congested
state. This is achieved by tracking congested state via
bdi_writeback_congested structs which are keyed by blkcg.

bdi->wb remains unchanged and will keep serving the root cgroup.
cgwb's (cgroup wb's) for non-root cgroups are created on-demand or
looked up while dirtying an inode according to the memcg of the page
being dirtied or current task. Each cgwb is indexed on bdi->cgwb_tree
by its memcg id. Once an inode is associated with its wb, it can be
retrieved using inode_to_wb().

Currently, none of the filesystems has FS_CGROUP_WRITEBACK and all
pages will keep being associated with bdi->wb.

v3: inode_attach_wb() in account_page_dirtied() moved inside
mapping_cap_account_dirty() block where it's known to be !NULL.
Also, an unnecessary NULL check before kfree() removed. Both
detected by the kbuild bot.

v2: Updated so that wb association is per inode and wb is per memcg
rather than blkcg.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: kbuild test robot <fengguang.wu@intel.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
---
block/blk-cgroup.c | 7 +-
fs/fs-writeback.c | 8 +-
fs/inode.c | 1 +
include/linux/backing-dev-defs.h | 59 +++++-
include/linux/backing-dev.h | 195 +++++++++++++++++++
include/linux/blk-cgroup.h | 4 +
include/linux/fs.h | 4 +
include/linux/memcontrol.h | 4 +
mm/backing-dev.c | 397 +++++++++++++++++++++++++++++++++++++++
mm/memcontrol.c | 19 +-
mm/page-writeback.c | 11 +-
11 files changed, 698 insertions(+), 11 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 54ec172..979cfdb 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -15,6 +15,7 @@
#include <linux/module.h>
#include <linux/err.h>
#include <linux/blkdev.h>
+#include <linux/backing-dev.h>
#include <linux/slab.h>
#include <linux/genhd.h>
#include <linux/delay.h>
@@ -797,6 +798,8 @@ static void blkcg_css_offline(struct cgroup_subsys_state *css)
}

spin_unlock_irq(&blkcg->lock);
+
+ wb_blkcg_offline(blkcg);
}

static void blkcg_css_free(struct cgroup_subsys_state *css)
@@ -827,7 +830,9 @@ done:
spin_lock_init(&blkcg->lock);
INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_ATOMIC);
INIT_HLIST_HEAD(&blkcg->blkg_list);
-
+#ifdef CONFIG_CGROUP_WRITEBACK
+ INIT_LIST_HEAD(&blkcg->cgwb_list);
+#endif
return &blkcg->css;
}

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 4fd264d..48db5e6 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -173,11 +173,11 @@ void bdi_start_background_writeback(struct backing_dev_info *bdi)
*/
void inode_wb_list_del(struct inode *inode)
{
- struct backing_dev_info *bdi = inode_to_bdi(inode);
+ struct bdi_writeback *wb = inode_to_wb(inode);

- spin_lock(&bdi->wb.list_lock);
+ spin_lock(&wb->list_lock);
list_del_init(&inode->i_wb_list);
- spin_unlock(&bdi->wb.list_lock);
+ spin_unlock(&wb->list_lock);
}

/*
@@ -1200,6 +1200,8 @@ void __mark_inode_dirty(struct inode *inode, int flags)
if ((inode->i_state & flags) != flags) {
const int was_dirty = inode->i_state & I_DIRTY;

+ inode_attach_wb(inode, NULL);
+
if (flags & I_DIRTY_INODE)
inode->i_state &= ~I_DIRTY_TIME;
inode->i_state |= flags;
diff --git a/fs/inode.c b/fs/inode.c
index f00b16f..55cedf8 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -223,6 +223,7 @@ EXPORT_SYMBOL(free_inode_nonrcu);
void __destroy_inode(struct inode *inode)
{
BUG_ON(inode_has_buffers(inode));
+ inode_detach_wb(inode);
security_inode_free(inode);
fsnotify_inode_delete(inode);
locks_free_lock_context(inode->i_flctx);
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 9e9eafa..a1e9c40 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -2,8 +2,11 @@
#define __LINUX_BACKING_DEV_DEFS_H

#include <linux/list.h>
+#include <linux/radix-tree.h>
+#include <linux/rbtree.h>
#include <linux/spinlock.h>
#include <linux/percpu_counter.h>
+#include <linux/percpu-refcount.h>
#include <linux/flex_proportions.h>
#include <linux/timer.h>
#include <linux/workqueue.h>
@@ -37,10 +40,43 @@ enum wb_stat_item {

#define WB_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))

+/*
+ * For cgroup writeback, multiple wb's may map to the same blkcg. Those
+ * wb's can operate mostly independently but should share the congested
+ * state. To facilitate such sharing, the congested state is tracked using
+ * the following struct which is created on demand, indexed by blkcg ID on
+ * its bdi, and refcounted.
+ */
struct bdi_writeback_congested {
unsigned long state; /* WB_[a]sync_congested flags */
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+ struct backing_dev_info *bdi; /* the associated bdi */
+ atomic_t refcnt; /* nr of attached wb's and blkg */
+ int blkcg_id; /* ID of the associated blkcg */
+ struct rb_node rb_node; /* on bdi->cgwb_congestion_tree */
+#endif
};

+/*
+ * Each wb (bdi_writeback) can perform writeback operations, is measured
+ * and throttled, independently. Without cgroup writeback, each bdi
+ * (bdi_writeback) is served by its embedded bdi->wb.
+ *
+ * On the default hierarchy, blkcg implicitly enables memcg. This allows
+ * using memcg's page ownership for attributing writeback IOs, and every
+ * memcg - blkcg combination can be served by its own wb by assigning a
+ * dedicated wb to each memcg, which enables isolation across different
+ * cgroups and propagation of IO back pressure down from the IO layer upto
+ * the tasks which are generating the dirty pages to be written back.
+ *
+ * A cgroup wb is indexed on its bdi by the ID of the associated memcg,
+ * refcounted with the number of inodes attached to it, and pins the memcg
+ * and the corresponding blkcg. As the corresponding blkcg for a memcg may
+ * change as blkcg is disabled and enabled higher up in the hierarchy, a wb
+ * is tested for blkcg after lookup and removed from index on mismatch so
+ * that a new wb for the combination can be created.
+ */
struct bdi_writeback {
struct backing_dev_info *bdi; /* our parent bdi */

@@ -78,6 +114,19 @@ struct bdi_writeback {
spinlock_t work_lock; /* protects work_list & dwork scheduling */
struct list_head work_list;
struct delayed_work dwork; /* work item used for writeback */
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+ struct percpu_ref refcnt; /* used only for !root wb's */
+ struct cgroup_subsys_state *memcg_css; /* the associated memcg */
+ struct cgroup_subsys_state *blkcg_css; /* and blkcg */
+ struct list_head memcg_node; /* anchored at memcg->cgwb_list */
+ struct list_head blkcg_node; /* anchored at blkcg->cgwb_list */
+
+ union {
+ struct work_struct release_work;
+ struct rcu_head rcu;
+ };
+#endif
};

struct backing_dev_info {
@@ -92,9 +141,13 @@ struct backing_dev_info {
unsigned int min_ratio;
unsigned int max_ratio, max_prop_frac;

- struct bdi_writeback wb; /* default writeback info for this bdi */
- struct bdi_writeback_congested wb_congested;
-
+ struct bdi_writeback wb; /* the root writeback info for this bdi */
+ struct bdi_writeback_congested wb_congested; /* its congested state */
+#ifdef CONFIG_CGROUP_WRITEBACK
+ struct radix_tree_root cgwb_tree; /* radix tree of active cgroup wbs */
+ struct rb_root cgwb_congested_tree; /* their congested states */
+ atomic_t usage_cnt; /* counts both cgwbs and cgwb_contested's */
+#endif
struct device *dev;

struct timer_list laptop_mode_wb_timer;
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 6bb3123..8ae59df 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -13,6 +13,7 @@
#include <linux/sched.h>
#include <linux/blkdev.h>
#include <linux/writeback.h>
+#include <linux/blk-cgroup.h>
#include <linux/backing-dev-defs.h>

int __must_check bdi_init(struct backing_dev_info *bdi);
@@ -234,6 +235,16 @@ static inline int bdi_sched_wait(void *word)

#ifdef CONFIG_CGROUP_WRITEBACK

+struct bdi_writeback_congested *
+wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp);
+void wb_congested_put(struct bdi_writeback_congested *congested);
+struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
+ struct cgroup_subsys_state *memcg_css,
+ gfp_t gfp);
+void __inode_attach_wb(struct inode *inode, struct page *page);
+void wb_memcg_offline(struct mem_cgroup *memcg);
+void wb_blkcg_offline(struct blkcg *blkcg);
+
/**
* inode_cgwb_enabled - test whether cgroup writeback is enabled on an inode
* @inode: inode of interest
@@ -250,6 +261,135 @@ static inline bool inode_cgwb_enabled(struct inode *inode)
(inode->i_sb->s_type->fs_flags & FS_CGROUP_WRITEBACK);
}

+/**
+ * wb_tryget - try to increment a wb's refcount
+ * @wb: bdi_writeback to get
+ */
+static inline bool wb_tryget(struct bdi_writeback *wb)
+{
+ if (wb != &wb->bdi->wb)
+ return percpu_ref_tryget(&wb->refcnt);
+ return true;
+}
+
+/**
+ * wb_get - increment a wb's refcount
+ * @wb: bdi_writeback to get
+ */
+static inline void wb_get(struct bdi_writeback *wb)
+{
+ if (wb != &wb->bdi->wb)
+ percpu_ref_get(&wb->refcnt);
+}
+
+/**
+ * wb_put - decrement a wb's refcount
+ * @wb: bdi_writeback to put
+ */
+static inline void wb_put(struct bdi_writeback *wb)
+{
+ if (wb != &wb->bdi->wb)
+ percpu_ref_put(&wb->refcnt);
+}
+
+/**
+ * wb_find_current - find wb for %current on a bdi
+ * @bdi: bdi of interest
+ *
+ * Find the wb of @bdi which matches both the memcg and blkcg of %current.
+ * Must be called under rcu_read_lock() which protects the returend wb.
+ * NULL if not found.
+ */
+static inline struct bdi_writeback *wb_find_current(struct backing_dev_info *bdi)
+{
+ struct cgroup_subsys_state *memcg_css;
+ struct bdi_writeback *wb;
+
+ memcg_css = task_css(current, memory_cgrp_id);
+ if (!memcg_css->parent)
+ return &bdi->wb;
+
+ wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
+
+ /*
+ * %current's blkcg equals the effective blkcg of its memcg. No
+ * need to use the relatively expensive cgroup_get_e_css().
+ */
+ if (likely(wb && wb->blkcg_css == task_css(current, blkio_cgrp_id)))
+ return wb;
+ return NULL;
+}
+
+/**
+ * wb_get_create_current - get or create wb for %current on a bdi
+ * @bdi: bdi of interest
+ * @gfp: allocation mask
+ *
+ * Equivalent to wb_get_create() on %current's memcg. This function is
+ * called from a relatively hot path and optimizes the common cases using
+ * wb_find_current().
+ */
+static inline struct bdi_writeback *
+wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
+{
+ struct bdi_writeback *wb;
+
+ rcu_read_lock();
+ wb = wb_find_current(bdi);
+ if (wb && unlikely(!wb_tryget(wb)))
+ wb = NULL;
+ rcu_read_unlock();
+
+ if (unlikely(!wb)) {
+ struct cgroup_subsys_state *memcg_css;
+
+ memcg_css = task_get_css(current, memory_cgrp_id);
+ wb = wb_get_create(bdi, memcg_css, gfp);
+ css_put(memcg_css);
+ }
+ return wb;
+}
+
+/**
+ * inode_attach_wb - associate an inode with its wb
+ * @inode: inode of interest
+ * @page: page being dirtied (may be NULL)
+ *
+ * If @inode doesn't have its wb, associate it with the wb matching the
+ * memcg of @page or, if @page is NULL, %current. May be called w/ or w/o
+ * @inode->i_lock.
+ */
+static inline void inode_attach_wb(struct inode *inode, struct page *page)
+{
+ if (!inode->i_wb)
+ __inode_attach_wb(inode, page);
+}
+
+/**
+ * inode_detach_wb - disassociate an inode from its wb
+ * @inode: inode of interest
+ *
+ * @inode is being freed. Detach from its wb.
+ */
+static inline void inode_detach_wb(struct inode *inode)
+{
+ if (inode->i_wb) {
+ wb_put(inode->i_wb);
+ inode->i_wb = NULL;
+ }
+}
+
+/**
+ * inode_to_wb - determine the wb of an inode
+ * @inode: inode of interest
+ *
+ * Returns the wb @inode is currently associated with.
+ */
+static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
+{
+ return inode->i_wb;
+}
+
#else /* CONFIG_CGROUP_WRITEBACK */

static inline bool inode_cgwb_enabled(struct inode *inode)
@@ -257,6 +397,61 @@ static inline bool inode_cgwb_enabled(struct inode *inode)
return false;
}

+static inline struct bdi_writeback_congested *
+wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
+{
+ return bdi->wb.congested;
+}
+
+static inline void wb_congested_put(struct bdi_writeback_congested *congested)
+{
+}
+
+static inline bool wb_tryget(struct bdi_writeback *wb)
+{
+ return true;
+}
+
+static inline void wb_get(struct bdi_writeback *wb)
+{
+}
+
+static inline void wb_put(struct bdi_writeback *wb)
+{
+}
+
+static inline struct bdi_writeback *wb_find_current(struct backing_dev_info *bdi)
+{
+ return &bdi->wb;
+}
+
+static inline struct bdi_writeback *
+wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
+{
+ return &bdi->wb;
+}
+
+static inline void inode_attach_wb(struct inode *inode, struct page *page)
+{
+}
+
+static inline void inode_detach_wb(struct inode *inode)
+{
+}
+
+static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
+{
+ return &inode_to_bdi(inode)->wb;
+}
+
+static inline void wb_memcg_offline(struct mem_cgroup *memcg)
+{
+}
+
+static inline void wb_blkcg_offline(struct blkcg *blkcg)
+{
+}
+
#endif /* CONFIG_CGROUP_WRITEBACK */

#endif /* _LINUX_BACKING_DEV_H */
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 4dc643f..3033eb1 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -53,6 +53,10 @@ struct blkcg {
/* TODO: per-policy storage in blkcg */
unsigned int cfq_weight; /* belongs to cfq */
unsigned int cfq_leaf_weight;
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+ struct list_head cgwb_list;
+#endif
};

struct blkg_stat {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index bc72737..4c740ca 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -35,6 +35,7 @@
#include <uapi/linux/fs.h>

struct backing_dev_info;
+struct bdi_writeback;
struct export_operations;
struct hd_geometry;
struct iovec;
@@ -607,6 +608,9 @@ struct inode {

struct hlist_node i_hash;
struct list_head i_wb_list; /* backing dev IO list */
+#ifdef CONFIG_CGROUP_WRITEBACK
+ struct bdi_writeback *i_wb; /* the associated cgroup wb */
+#endif
struct list_head i_lru; /* inode LRU list */
struct list_head i_sb_list;
union {
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 637ef62..662a953 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -388,6 +388,10 @@ enum {
OVER_LIMIT,
};

+#ifdef CONFIG_CGROUP_WRITEBACK
+struct list_head *mem_cgroup_cgwb_list(struct mem_cgroup *memcg);
+#endif
+
struct sock;
#if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)
void sock_update_memcg(struct sock *sk);
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 5ec7658..4c9386c 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -368,6 +368,401 @@ static void wb_exit(struct bdi_writeback *wb)
fprop_local_destroy_percpu(&wb->completions);
}

+#ifdef CONFIG_CGROUP_WRITEBACK
+
+#include <linux/memcontrol.h>
+
+/*
+ * cgwb_lock protects bdi->cgwb_tree, bdi->cgwb_congested_tree,
+ * blkcg->cgwb_list, and memcg->cgwb_list. bdi->cgwb_tree is also RCU
+ * protected. cgwb_release_wait is used to wait for the completion of cgwb
+ * releases from bdi destruction path.
+ */
+static DEFINE_SPINLOCK(cgwb_lock);
+static DECLARE_WAIT_QUEUE_HEAD(cgwb_release_wait);
+
+/**
+ * wb_congested_get_create - get or create a wb_congested
+ * @bdi: associated bdi
+ * @blkcg_id: ID of the associated blkcg
+ * @gfp: allocation mask
+ *
+ * Look up the wb_congested for @blkcg_id on @bdi. If missing, create one.
+ * The returned wb_congested has its reference count incremented. Returns
+ * NULL on failure.
+ */
+struct bdi_writeback_congested *
+wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
+{
+ struct bdi_writeback_congested *new_congested = NULL, *congested;
+ struct rb_node **node, *parent;
+ unsigned long flags;
+
+ if (blkcg_id == 1)
+ return &bdi->wb_congested;
+retry:
+ spin_lock_irqsave(&cgwb_lock, flags);
+
+ node = &bdi->cgwb_congested_tree.rb_node;
+ parent = NULL;
+
+ while (*node != NULL) {
+ parent = *node;
+ congested = container_of(parent, struct bdi_writeback_congested,
+ rb_node);
+ if (congested->blkcg_id < blkcg_id)
+ node = &parent->rb_left;
+ else if (congested->blkcg_id > blkcg_id)
+ node = &parent->rb_right;
+ else
+ goto found;
+ }
+
+ if (new_congested) {
+ /* !found and storage for new one already allocated, insert */
+ congested = new_congested;
+ new_congested = NULL;
+ rb_link_node(&congested->rb_node, parent, node);
+ rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
+ atomic_inc(&bdi->usage_cnt);
+ goto found;
+ }
+
+ spin_unlock_irqrestore(&cgwb_lock, flags);
+
+ /* allocate storage for new one and retry */
+ new_congested = kzalloc(sizeof(*new_congested), gfp);
+ if (!new_congested)
+ return NULL;
+
+ atomic_set(&new_congested->refcnt, 0);
+ new_congested->bdi = bdi;
+ new_congested->blkcg_id = blkcg_id;
+ goto retry;
+
+found:
+ atomic_inc(&congested->refcnt);
+ spin_unlock_irqrestore(&cgwb_lock, flags);
+ kfree(new_congested);
+ return congested;
+}
+
+/**
+ * wb_congested_put - put a wb_congested
+ * @congested: wb_congested to put
+ *
+ * Put @congested and destroy it if the refcnt reaches zero.
+ */
+void wb_congested_put(struct bdi_writeback_congested *congested)
+{
+ struct backing_dev_info *bdi = congested->bdi;
+ unsigned long flags;
+
+ if (congested->blkcg_id == 1)
+ return;
+
+ local_irq_save(flags);
+ if (!atomic_dec_and_lock(&congested->refcnt, &cgwb_lock)) {
+ local_irq_restore(flags);
+ return;
+ }
+
+ rb_erase(&congested->rb_node, &congested->bdi->cgwb_congested_tree);
+ spin_unlock_irqrestore(&cgwb_lock, flags);
+ kfree(congested);
+
+ if (atomic_dec_and_test(&bdi->usage_cnt))
+ wake_up_all(&cgwb_release_wait);
+}
+
+static void cgwb_release_workfn(struct work_struct *work)
+{
+ struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
+ release_work);
+ struct backing_dev_info *bdi = wb->bdi;
+
+ wb_shutdown(wb);
+
+ css_put(wb->memcg_css);
+ css_put(wb->blkcg_css);
+ wb_congested_put(wb->congested);
+
+ percpu_ref_exit(&wb->refcnt);
+ wb_exit(wb);
+ kfree_rcu(wb, rcu);
+
+ if (atomic_dec_and_test(&bdi->usage_cnt))
+ wake_up_all(&cgwb_release_wait);
+}
+
+static void cgwb_release(struct percpu_ref *refcnt)
+{
+ struct bdi_writeback *wb = container_of(refcnt, struct bdi_writeback,
+ refcnt);
+ schedule_work(&wb->release_work);
+}
+
+static void cgwb_kill(struct bdi_writeback *wb)
+{
+ lockdep_assert_held(&cgwb_lock);
+
+ WARN_ON(!radix_tree_delete(&wb->bdi->cgwb_tree, wb->memcg_css->id));
+ list_del(&wb->memcg_node);
+ list_del(&wb->blkcg_node);
+ percpu_ref_kill(&wb->refcnt);
+}
+
+static int cgwb_create(struct backing_dev_info *bdi,
+ struct cgroup_subsys_state *memcg_css, gfp_t gfp)
+{
+ struct mem_cgroup *memcg;
+ struct cgroup_subsys_state *blkcg_css;
+ struct blkcg *blkcg;
+ struct list_head *memcg_cgwb_list, *blkcg_cgwb_list;
+ struct bdi_writeback *wb;
+ unsigned long flags;
+ int ret = 0;
+
+ memcg = mem_cgroup_from_css(memcg_css);
+ blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &blkio_cgrp_subsys);
+ blkcg = css_to_blkcg(blkcg_css);
+ memcg_cgwb_list = mem_cgroup_cgwb_list(memcg);
+ blkcg_cgwb_list = &blkcg->cgwb_list;
+
+ /* look up again under lock and discard on blkcg mismatch */
+ spin_lock_irqsave(&cgwb_lock, flags);
+ wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
+ if (wb && wb->blkcg_css != blkcg_css) {
+ cgwb_kill(wb);
+ wb = NULL;
+ }
+ spin_unlock_irqrestore(&cgwb_lock, flags);
+ if (wb)
+ goto out_put;
+
+ /* need to create a new one */
+ wb = kmalloc(sizeof(*wb), gfp);
+ if (!wb)
+ return -ENOMEM;
+
+ ret = wb_init(wb, bdi, gfp);
+ if (ret)
+ goto err_free;
+
+ ret = percpu_ref_init(&wb->refcnt, cgwb_release, 0, gfp);
+ if (ret)
+ goto err_wb_exit;
+
+ wb->congested = wb_congested_get_create(bdi, blkcg_css->id, gfp);
+ if (!wb->congested)
+ goto err_ref_exit;
+
+ wb->memcg_css = memcg_css;
+ wb->blkcg_css = blkcg_css;
+ INIT_WORK(&wb->release_work, cgwb_release_workfn);
+ set_bit(WB_registered, &wb->state);
+
+ /*
+ * The root wb determines the registered state of the whole bdi and
+ * memcg_cgwb_list and blkcg_cgwb_list's next pointers indicate
+ * whether they're still online. Don't link @wb if any is dead.
+ * See wb_memcg_offline() and wb_blkcg_offline().
+ */
+ ret = -ENODEV;
+ spin_lock_irqsave(&cgwb_lock, flags);
+ if (test_bit(WB_registered, &bdi->wb.state) &&
+ blkcg_cgwb_list->next && memcg_cgwb_list->next) {
+ /* we might have raced another instance of this function */
+ ret = radix_tree_insert(&bdi->cgwb_tree, memcg_css->id, wb);
+ if (!ret) {
+ atomic_inc(&bdi->usage_cnt);
+ list_add(&wb->memcg_node, memcg_cgwb_list);
+ list_add(&wb->blkcg_node, blkcg_cgwb_list);
+ css_get(memcg_css);
+ css_get(blkcg_css);
+ }
+ }
+ spin_unlock_irqrestore(&cgwb_lock, flags);
+ if (ret) {
+ if (ret == -EEXIST)
+ ret = 0;
+ goto err_put_congested;
+ }
+ goto out_put;
+
+err_put_congested:
+ wb_congested_put(wb->congested);
+err_ref_exit:
+ percpu_ref_exit(&wb->refcnt);
+err_wb_exit:
+ wb_exit(wb);
+err_free:
+ kfree(wb);
+out_put:
+ css_put(blkcg_css);
+ return ret;
+}
+
+/**
+ * wb_get_create - get wb for a given memcg, create if necessary
+ * @bdi: target bdi
+ * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
+ * @gfp: allocation mask to use
+ *
+ * Try to get the wb for @memcg_css on @bdi. If it doesn't exist, try to
+ * create one. The returned wb has its refcount incremented.
+ *
+ * This function uses css_get() on @memcg_css and thus expects its refcnt
+ * to be positive on invocation. IOW, rcu_read_lock() protection on
+ * @memcg_css isn't enough. try_get it before calling this function.
+ *
+ * A wb is keyed by its associated memcg. As blkcg implicitly enables
+ * memcg on the default hierarchy, memcg association is guaranteed to be
+ * more specific (equal or descendant to the associated blkcg) and thus can
+ * identify both the memcg and blkcg associations.
+ *
+ * Because the blkcg associated with a memcg may change as blkcg is enabled
+ * and disabled closer to root in the hierarchy, each wb keeps track of
+ * both the memcg and blkcg associated with it and verifies the blkcg on
+ * each lookup. On mismatch, the existing wb is discarded and a new one is
+ * created.
+ */
+struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
+ struct cgroup_subsys_state *memcg_css,
+ gfp_t gfp)
+{
+ struct bdi_writeback *wb;
+
+ might_sleep_if(gfp & __GFP_WAIT);
+
+ if (!memcg_css->parent)
+ return &bdi->wb;
+
+ do {
+ rcu_read_lock();
+ wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
+ if (wb) {
+ struct cgroup_subsys_state *blkcg_css;
+
+ /* see whether the blkcg association has changed */
+ blkcg_css = cgroup_get_e_css(memcg_css->cgroup,
+ &blkio_cgrp_subsys);
+ if (unlikely(wb->blkcg_css != blkcg_css ||
+ !wb_tryget(wb)))
+ wb = NULL;
+ css_put(blkcg_css);
+ }
+ rcu_read_unlock();
+ } while (!wb && !cgwb_create(bdi, memcg_css, gfp));
+
+ return wb;
+}
+
+void __inode_attach_wb(struct inode *inode, struct page *page)
+{
+ struct backing_dev_info *bdi = inode_to_bdi(inode);
+ struct bdi_writeback *wb = NULL;
+
+ if (inode_cgwb_enabled(inode)) {
+ struct cgroup_subsys_state *memcg_css;
+
+ if (page) {
+ memcg_css = mem_cgroup_css_from_page(page);
+ wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
+ } else {
+ /* must pin memcg_css, see wb_get_create() */
+ memcg_css = task_get_css(current, memory_cgrp_id);
+ wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
+ css_put(memcg_css);
+ }
+ }
+
+ if (!wb)
+ wb = &bdi->wb;
+
+ /*
+ * There may be multiple instances of this function racing to
+ * update the same inode. Use cmpxchg() to tell the winner.
+ */
+ if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
+ wb_put(wb);
+}
+
+static void cgwb_bdi_init(struct backing_dev_info *bdi)
+{
+ bdi->wb.memcg_css = mem_cgroup_root_css;
+ bdi->wb.blkcg_css = blkcg_root_css;
+ bdi->wb_congested.blkcg_id = 1;
+ INIT_RADIX_TREE(&bdi->cgwb_tree, GFP_ATOMIC);
+ bdi->cgwb_congested_tree = RB_ROOT;
+ atomic_set(&bdi->usage_cnt, 1);
+}
+
+static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
+{
+ struct radix_tree_iter iter;
+ void **slot;
+
+ WARN_ON(test_bit(WB_registered, &bdi->wb.state));
+
+ spin_lock_irq(&cgwb_lock);
+ radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
+ cgwb_kill(*slot);
+ spin_unlock_irq(&cgwb_lock);
+
+ /*
+ * All cgwb's and their congested states must be shutdown and
+ * released before returning. Drain the usage counter to wait for
+ * all cgwb's and cgwb_congested's ever created on @bdi.
+ */
+ atomic_dec(&bdi->usage_cnt);
+ wait_event(cgwb_release_wait, !atomic_read(&bdi->usage_cnt));
+}
+
+/**
+ * wb_memcg_offline - kill all wb's associated with a memcg being offlined
+ * @memcg: memcg being offlined
+ *
+ * Also prevents creation of any new wb's associated with @memcg.
+ */
+void wb_memcg_offline(struct mem_cgroup *memcg)
+{
+ LIST_HEAD(to_destroy);
+ struct list_head *memcg_cgwb_list = mem_cgroup_cgwb_list(memcg);
+ struct bdi_writeback *wb, *next;
+
+ spin_lock_irq(&cgwb_lock);
+ list_for_each_entry_safe(wb, next, memcg_cgwb_list, memcg_node)
+ cgwb_kill(wb);
+ memcg_cgwb_list->next = NULL; /* prevent new wb's */
+ spin_unlock_irq(&cgwb_lock);
+}
+
+/**
+ * wb_blkcg_offline - kill all wb's associated with a blkcg being offlined
+ * @blkcg: blkcg being offlined
+ *
+ * Also prevents creation of any new wb's associated with @blkcg.
+ */
+void wb_blkcg_offline(struct blkcg *blkcg)
+{
+ LIST_HEAD(to_destroy);
+ struct bdi_writeback *wb, *next;
+
+ spin_lock_irq(&cgwb_lock);
+ list_for_each_entry_safe(wb, next, &blkcg->cgwb_list, blkcg_node)
+ cgwb_kill(wb);
+ blkcg->cgwb_list.next = NULL; /* prevent new wb's */
+ spin_unlock_irq(&cgwb_lock);
+}
+
+#else /* CONFIG_CGROUP_WRITEBACK */
+
+static void cgwb_bdi_init(struct backing_dev_info *bdi) { }
+static void cgwb_bdi_destroy(struct backing_dev_info *bdi) { }
+
+#endif /* CONFIG_CGROUP_WRITEBACK */
+
int bdi_init(struct backing_dev_info *bdi)
{
int err;
@@ -386,6 +781,7 @@ int bdi_init(struct backing_dev_info *bdi)
bdi->wb_congested.state = 0;
bdi->wb.congested = &bdi->wb_congested;

+ cgwb_bdi_init(bdi);
return 0;
}
EXPORT_SYMBOL(bdi_init);
@@ -459,6 +855,7 @@ void bdi_destroy(struct backing_dev_info *bdi)
/* make sure nobody finds us on the bdi_list anymore */
bdi_remove_from_list(bdi);
wb_shutdown(&bdi->wb);
+ cgwb_bdi_destroy(bdi);

if (bdi->dev) {
bdi_debug_unregister(bdi);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 74241b3..a6fa6fe 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -347,6 +347,10 @@ struct mem_cgroup {
atomic_t numainfo_updating;
#endif

+#ifdef CONFIG_CGROUP_WRITEBACK
+ struct list_head cgwb_list;
+#endif
+
/* List of events which userspace want to receive */
struct list_head event_list;
spinlock_t event_list_lock;
@@ -4121,6 +4125,15 @@ static void memcg_destroy_kmem(struct mem_cgroup *memcg)
}
#endif

+#ifdef CONFIG_CGROUP_WRITEBACK
+
+struct list_head *mem_cgroup_cgwb_list(struct mem_cgroup *memcg)
+{
+ return &memcg->cgwb_list;
+}
+
+#endif /* CONFIG_CGROUP_WRITEBACK */
+
/*
* DO NOT USE IN NEW FILES.
*
@@ -4585,7 +4598,9 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
#ifdef CONFIG_MEMCG_KMEM
memcg->kmemcg_id = -1;
#endif
-
+#ifdef CONFIG_CGROUP_WRITEBACK
+ INIT_LIST_HEAD(&memcg->cgwb_list);
+#endif
return &memcg->css;

free_out:
@@ -4673,6 +4688,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
vmpressure_cleanup(&memcg->vmpressure);

memcg_deactivate_kmem(memcg);
+
+ wb_memcg_offline(memcg);
}

static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c615a15..79c9026 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2097,16 +2097,21 @@ int __set_page_dirty_no_writeback(struct page *page)
void account_page_dirtied(struct page *page, struct address_space *mapping,
struct mem_cgroup *memcg)
{
+ struct inode *inode = mapping->host;
+
trace_writeback_dirty_page(page, mapping);

if (mapping_cap_account_dirty(mapping)) {
- struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+ struct bdi_writeback *wb;
+
+ inode_attach_wb(inode, page);
+ wb = inode_to_wb(inode);

mem_cgroup_inc_page_stat(memcg, MEM_CGROUP_STAT_DIRTY);
__inc_zone_page_state(page, NR_FILE_DIRTY);
__inc_zone_page_state(page, NR_DIRTIED);
- __inc_wb_stat(&bdi->wb, WB_RECLAIMABLE);
- __inc_wb_stat(&bdi->wb, WB_DIRTIED);
+ __inc_wb_stat(wb, WB_RECLAIMABLE);
+ __inc_wb_stat(wb, WB_DIRTIED);
task_io_account_write(PAGE_CACHE_SIZE);
current->nr_dirtied++;
this_cpu_inc(bdp_ratelimits);
--
2.1.0