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Message-ID: <20150926221413.GI3572@htj.duckdns.org>
Date: Sat, 26 Sep 2015 18:14:13 -0400
From: Tejun Heo <tj@...nel.org>
To: Artem Bityutskiy <dedekind1@...il.com>
Cc: Theodore Ts'o <tytso@....edu>, axboe@...nel.dk,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
lizefan@...wei.com, cgroups@...r.kernel.org, hannes@...xchg.org,
kernel-team@...com, adilger.kernel@...ger.ca,
linux-ext4@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH cgroup/for-4.3-fixes] cgroup, writeback: don't enable
cgroup writeback on traditional hierarchies
Hello, Artem.
Thanks a lot for the debug dump. Can you please test whether the
below patch fixes the issue?
Index: work/mm/page-writeback.c
===================================================================
--- work.orig/mm/page-writeback.c
+++ work/mm/page-writeback.c
@@ -1956,7 +1956,6 @@ void laptop_mode_timer_fn(unsigned long
int nr_pages = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
struct bdi_writeback *wb;
- struct wb_iter iter;
/*
* We want to write everything out, not just down to the dirty
@@ -1965,10 +1964,12 @@ void laptop_mode_timer_fn(unsigned long
if (!bdi_has_dirty_io(&q->backing_dev_info))
return;
- bdi_for_each_wb(wb, &q->backing_dev_info, &iter, 0)
+ rcu_read_lock();
+ list_for_each_entry_rcu(wb, &q->backing_dev_info.wb_list, bdi_node)
if (wb_has_dirty_io(wb))
wb_start_writeback(wb, nr_pages, true,
WB_REASON_LAPTOP_TIMER);
+ rcu_read_unlock();
}
/*
Index: work/fs/fs-writeback.c
===================================================================
--- work.orig/fs/fs-writeback.c
+++ work/fs/fs-writeback.c
@@ -778,19 +778,24 @@ static void bdi_split_work_to_wbs(struct
struct wb_writeback_work *base_work,
bool skip_if_busy)
{
- int next_memcg_id = 0;
- struct bdi_writeback *wb;
- struct wb_iter iter;
+ struct bdi_writeback *last_wb = NULL;
+ struct bdi_writeback *wb = list_entry_rcu(&bdi->wb_list,
+ struct bdi_writeback, bdi_node);
might_sleep();
restart:
rcu_read_lock();
- bdi_for_each_wb(wb, bdi, &iter, next_memcg_id) {
+ list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
DEFINE_WB_COMPLETION_ONSTACK(fallback_work_done);
struct wb_writeback_work fallback_work;
struct wb_writeback_work *work;
long nr_pages;
+ if (last_wb) {
+ wb_put(last_wb);
+ last_wb = NULL;
+ }
+
/* SYNC_ALL writes out I_DIRTY_TIME too */
if (!wb_has_dirty_io(wb) &&
(base_work->sync_mode == WB_SYNC_NONE ||
@@ -819,7 +824,14 @@ restart:
wb_queue_work(wb, work);
- next_memcg_id = wb->memcg_css->id + 1;
+ /*
+ * Pin @wb so that it stays on @bdi->wb_list. This allows
+ * continuing iteration from @wb after dropping regrabbing
+ * rcu read lock.
+ */
+ wb_get(wb);
+ last_wb = wb;
+
rcu_read_unlock();
wb_wait_for_completion(bdi, &fallback_work_done);
goto restart;
@@ -1857,12 +1869,11 @@ void wakeup_flusher_threads(long nr_page
rcu_read_lock();
list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
struct bdi_writeback *wb;
- struct wb_iter iter;
if (!bdi_has_dirty_io(bdi))
continue;
- bdi_for_each_wb(wb, bdi, &iter, 0)
+ list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
wb_start_writeback(wb, wb_split_bdi_pages(wb, nr_pages),
false, reason);
}
@@ -1894,11 +1905,10 @@ static void wakeup_dirtytime_writeback(s
rcu_read_lock();
list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
struct bdi_writeback *wb;
- struct wb_iter iter;
- bdi_for_each_wb(wb, bdi, &iter, 0)
- if (!list_empty(&bdi->wb.b_dirty_time))
- wb_wakeup(&bdi->wb);
+ list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
+ if (!list_empty(&wb->b_dirty_time))
+ wb_wakeup(wb);
}
rcu_read_unlock();
schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
Index: work/include/linux/backing-dev-defs.h
===================================================================
--- work.orig/include/linux/backing-dev-defs.h
+++ work/include/linux/backing-dev-defs.h
@@ -116,6 +116,8 @@ struct bdi_writeback {
struct list_head work_list;
struct delayed_work dwork; /* work item used for writeback */
+ struct list_head bdi_node; /* anchored at bdi->wb_list */
+
#ifdef CONFIG_CGROUP_WRITEBACK
struct percpu_ref refcnt; /* used only for !root wb's */
struct fprop_local_percpu memcg_completions;
@@ -150,6 +152,7 @@ struct backing_dev_info {
atomic_long_t tot_write_bandwidth;
struct bdi_writeback wb; /* the root writeback info for this bdi */
+ struct list_head wb_list; /* list of all wbs */
#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 */
Index: work/include/linux/backing-dev.h
===================================================================
--- work.orig/include/linux/backing-dev.h
+++ work/include/linux/backing-dev.h
@@ -401,61 +401,6 @@ static inline void unlocked_inode_to_wb_
rcu_read_unlock();
}
-struct wb_iter {
- int start_memcg_id;
- struct radix_tree_iter tree_iter;
- void **slot;
-};
-
-static inline struct bdi_writeback *__wb_iter_next(struct wb_iter *iter,
- struct backing_dev_info *bdi)
-{
- struct radix_tree_iter *titer = &iter->tree_iter;
-
- WARN_ON_ONCE(!rcu_read_lock_held());
-
- if (iter->start_memcg_id >= 0) {
- iter->slot = radix_tree_iter_init(titer, iter->start_memcg_id);
- iter->start_memcg_id = -1;
- } else {
- iter->slot = radix_tree_next_slot(iter->slot, titer, 0);
- }
-
- if (!iter->slot)
- iter->slot = radix_tree_next_chunk(&bdi->cgwb_tree, titer, 0);
- if (iter->slot)
- return *iter->slot;
- return NULL;
-}
-
-static inline struct bdi_writeback *__wb_iter_init(struct wb_iter *iter,
- struct backing_dev_info *bdi,
- int start_memcg_id)
-{
- iter->start_memcg_id = start_memcg_id;
-
- if (start_memcg_id)
- return __wb_iter_next(iter, bdi);
- else
- return &bdi->wb;
-}
-
-/**
- * bdi_for_each_wb - walk all wb's of a bdi in ascending memcg ID order
- * @wb_cur: cursor struct bdi_writeback pointer
- * @bdi: bdi to walk wb's of
- * @iter: pointer to struct wb_iter to be used as iteration buffer
- * @start_memcg_id: memcg ID to start iteration from
- *
- * Iterate @wb_cur through the wb's (bdi_writeback's) of @bdi in ascending
- * memcg ID order starting from @start_memcg_id. @iter is struct wb_iter
- * to be used as temp storage during iteration. rcu_read_lock() must be
- * held throughout iteration.
- */
-#define bdi_for_each_wb(wb_cur, bdi, iter, start_memcg_id) \
- for ((wb_cur) = __wb_iter_init(iter, bdi, start_memcg_id); \
- (wb_cur); (wb_cur) = __wb_iter_next(iter, bdi))
-
#else /* CONFIG_CGROUP_WRITEBACK */
static inline bool inode_cgwb_enabled(struct inode *inode)
@@ -515,14 +460,6 @@ static inline void wb_blkcg_offline(stru
{
}
-struct wb_iter {
- int next_id;
-};
-
-#define bdi_for_each_wb(wb_cur, bdi, iter, start_blkcg_id) \
- for ((iter)->next_id = (start_blkcg_id); \
- ({ (wb_cur) = !(iter)->next_id++ ? &(bdi)->wb : NULL; }); )
-
static inline int inode_congested(struct inode *inode, int cong_bits)
{
return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
Index: work/mm/backing-dev.c
===================================================================
--- work.orig/mm/backing-dev.c
+++ work/mm/backing-dev.c
@@ -480,6 +480,10 @@ static void cgwb_release_workfn(struct w
release_work);
struct backing_dev_info *bdi = wb->bdi;
+ spin_lock_irq(&cgwb_lock);
+ list_del_rcu(&wb->bdi_node);
+ spin_unlock_irq(&cgwb_lock);
+
wb_shutdown(wb);
css_put(wb->memcg_css);
@@ -575,6 +579,7 @@ static int cgwb_create(struct backing_de
ret = radix_tree_insert(&bdi->cgwb_tree, memcg_css->id, wb);
if (!ret) {
atomic_inc(&bdi->usage_cnt);
+ list_add_tail_rcu(&wb->bdi_node, &bdi->wb_list);
list_add(&wb->memcg_node, memcg_cgwb_list);
list_add(&wb->blkcg_node, blkcg_cgwb_list);
css_get(memcg_css);
@@ -669,6 +674,7 @@ static int cgwb_bdi_init(struct backing_
if (!ret) {
bdi->wb.memcg_css = mem_cgroup_root_css;
bdi->wb.blkcg_css = blkcg_root_css;
+ list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
}
return ret;
}
@@ -686,6 +692,9 @@ static void cgwb_bdi_destroy(struct back
radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
cgwb_kill(*slot);
+ /* release of wb's may happen after @bdi is freed, sever list head */
+ list_del(&bdi->wb_list);
+
rbtree_postorder_for_each_entry_safe(congested, congested_n,
&bdi->cgwb_congested_tree, rb_node) {
rb_erase(&congested->rb_node, &bdi->cgwb_congested_tree);
@@ -755,6 +764,9 @@ static int cgwb_bdi_init(struct backing_
kfree(bdi->wb_congested);
return err;
}
+
+ list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
+
return 0;
}
@@ -770,6 +782,7 @@ int bdi_init(struct backing_dev_info *bd
bdi->max_ratio = 100;
bdi->max_prop_frac = FPROP_FRAC_BASE;
INIT_LIST_HEAD(&bdi->bdi_list);
+ INIT_LIST_HEAD(&bdi->wb_list);
init_waitqueue_head(&bdi->wb_waitq);
return cgwb_bdi_init(bdi);
--
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