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Subject[RFC][PATCH v3 6/10] memcg : auto keep margin in background , workqueue core.

Core codes for controling workqueue for keeping margin to limit
in background. For contrling work, this patch adds 2 flags.

ASYNC_WORKER_RUNNING indicates the worker for memcg is scheduled and
"don't need to add new work". ASYNC_WORKER_SHOULD_STOP indicates that
someone is trying to remove the memcg and "stop async reclaim".
Because a worker need to hold a reference count for the memcg,
"stop work" is required at removing cgroup.

memory cgroup's automatic-keep-margin-to-limit work is scheduled
by memcg_async_shrinker workqueue which is configured as WQ_UNBOUND.

A shrinker core code mem_cgroup_shrink_rate_limited() will be
implemented in following patches.

Changelog:
- added comments and renamed flags.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
include/linux/swap.h | 3 +
mm/memcontrol.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++++--
mm/vmscan.c | 6 +++
3 files changed, 87 insertions(+), 2 deletions(-)
Index: memcg_async/mm/memcontrol.c
===================================================================
--- memcg_async.orig/mm/memcontrol.c
+++ memcg_async/mm/memcontrol.c
@@ -288,10 +288,12 @@ struct mem_cgroup {
*/
unsigned long margin_to_limit_pages; /* margin to limit */
spinlock_t update_margin_lock;
- unsigned long async_flags;
+ struct delayed_work async_work;
+ unsigned long async_flags;
#define AUTO_KEEP_MARGIN_ENABLED (0) /* user enabled async reclaim */
#define FAILED_TO_KEEP_MARGIN (1) /* someone hit limit */
-
+#define ASYNC_WORKER_RUNNING (2) /* a worker runs */
+#define ASYNC_WORKER_SHOULD_STOP (3) /* worker thread should stop */
/*
* percpu counter.
*/
@@ -3862,10 +3864,82 @@ static void mem_cgroup_reset_margin_to_l
}

/*
+ * Codes for reclaim memory in background with help of kworker.
+ * memory cgroup uses UNBOUND workqueue.
+ */
+struct workqueue_struct *memcg_async_shrinker;
+
+static int memcg_async_shrinker_init(void)
+{
+ memcg_async_shrinker = alloc_workqueue("memcg_async",
+ WQ_MEM_RECLAIM | WQ_UNBOUND | WQ_FREEZABLE, 0);
+ return 0;
+}
+module_init(memcg_async_shrinker_init);
+/*
+ * Called from rmdir() path and stop asynchronous worker because
+ * it has an extra reference count.
+ */
+static void mem_cgroup_stop_async_worker(struct mem_cgroup *mem)
+{
+ /* The worker will stop when see this flag */
+ set_bit(ASYNC_WORKER_SHOULD_STOP, &mem->async_flags);
+ flush_delayed_work(&mem->async_work);
+ clear_bit(ASYNC_WORKER_SHOULD_STOP, &mem->async_flags);
+}
+
+/*
+ * Reclaim memory in asynchronous way. This function is for getting
+ * enough margin to limit in background. If margin is enough big or
+ * someone tries to delete cgroup, stop reclaim.
+ * If margin is big even after shrink memory, reschedule itself again.
+ */
+static void mem_cgroup_async_shrink_worker(struct work_struct *work)
+{
+ struct delayed_work *dw = to_delayed_work(work);
+ struct mem_cgroup *mem;
+ int delay = 0;
+ long nr_to_reclaim;
+
+ mem = container_of(dw, struct mem_cgroup, async_work);
+
+ if (!test_bit(AUTO_KEEP_MARGIN_ENABLED, &mem->async_flags) ||
+ test_bit(ASYNC_WORKER_SHOULD_STOP, &mem->async_flags))
+ goto finish_scan;
+
+ nr_to_reclaim = mem->margin_to_limit_pages - mem_cgroup_margin(mem);
+
+ if (nr_to_reclaim > 0)
+ mem_cgroup_shrink_rate_limited(mem, nr_to_reclaim);
+ else
+ goto finish_scan;
+ /* If margin is enough big, stop */
+ if (mem_cgroup_margin(mem) >= mem->margin_to_limit_pages)
+ goto finish_scan;
+ /* If someone tries to rmdir(), we should stop */
+ if (test_bit(ASYNC_WORKER_SHOULD_STOP, &mem->async_flags))
+ goto finish_scan;
+
+ queue_delayed_work(memcg_async_shrinker, &mem->async_work, delay);
+ return;
+finish_scan:
+ cgroup_release_and_wakeup_rmdir(&mem->css);
+ clear_bit(ASYNC_WORKER_RUNNING, &mem->async_flags);
+ return;
+}
+
+/*
* Run a asynchronous memory reclaim on the memcg.
*/
static void mem_cgroup_schedule_async_reclaim(struct mem_cgroup *mem)
{
+ if (test_and_set_bit(ASYNC_WORKER_RUNNING, &mem->async_flags))
+ return;
+ cgroup_exclude_rmdir(&mem->css);
+ if (!queue_delayed_work(memcg_async_shrinker, &mem->async_work, 0)) {
+ cgroup_release_and_wakeup_rmdir(&mem->css);
+ clear_bit(ASYNC_WORKER_RUNNING, &mem->async_flags);
+ }
}

/*
@@ -3960,6 +4034,7 @@ static int mem_cgroup_force_empty(struct
move_account:
do {
ret = -EBUSY;
+ mem_cgroup_stop_async_worker(mem);
if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
goto out;
ret = -EINTR;
@@ -5239,6 +5314,7 @@ mem_cgroup_create(struct cgroup_subsys *
atomic_set(&mem->refcnt, 1);
mem->move_charge_at_immigrate = 0;
spin_lock_init(&mem->update_margin_lock);
+ INIT_DELAYED_WORK(&mem->async_work, mem_cgroup_async_shrink_worker);
mutex_init(&mem->thresholds_lock);
return &mem->css;
free_out:
Index: memcg_async/include/linux/swap.h
===================================================================
--- memcg_async.orig/include/linux/swap.h
+++ memcg_async/include/linux/swap.h
@@ -257,6 +257,9 @@ extern unsigned long mem_cgroup_shrink_n
gfp_t gfp_mask, bool noswap,
struct zone *zone,
unsigned long *nr_scanned);
+extern void mem_cgroup_shrink_rate_limited(struct mem_cgroup *mem,
+ unsigned long nr_to_reclaim);
+
extern int __isolate_lru_page(struct page *page, int mode, int file);
extern unsigned long shrink_all_memory(unsigned long nr_pages);
extern int vm_swappiness;
Index: memcg_async/mm/vmscan.c
===================================================================
--- memcg_async.orig/mm/vmscan.c
+++ memcg_async/mm/vmscan.c
@@ -2261,6 +2261,12 @@ unsigned long try_to_free_mem_cgroup_pag

return nr_reclaimed;
}
+
+void mem_cgroup_shrink_rate_limited(struct mem_cgroup *mem,
+ unsigned long nr_to_reclaim)
+{
+}
+
#endif

/*


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