[RFC PATCH 1/6] zram: deffer slot free notification

[Sergey Senozhatsky <senozhatsky@chromium.org>]

As of this moment ->swap_slot_free_notify is called from
atomic section (under spin-lock) which makes it impossible
to make zsmalloc fully preemptible.  Deffer slot-free to
a non-atomic context.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 66 +++++++++++++++++++++++++++++++++--
 drivers/block/zram/zram_drv.h |  4 +++
 2 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index ad3e8885b0d2..9c72beb86ab0 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -2315,9 +2315,52 @@ static void zram_submit_bio(struct bio *bio)
 	}
 }
 
+static void async_slot_free(struct work_struct *work)
+{
+	struct zram *zram = container_of(work, struct zram, slot_free_work);
+
+	spin_lock(&zram->slot_free_lock);
+	while (!list_empty(&zram->slot_free_list)) {
+		struct zram_pp_slot *pps;
+
+		pps = list_first_entry(&zram->slot_free_list,
+				       struct zram_pp_slot,
+				       entry);
+		list_del_init(&pps->entry);
+		spin_unlock(&zram->slot_free_lock);
+
+		zram_slot_write_lock(zram, pps->index);
+		if (zram_test_flag(zram, pps->index, ZRAM_PP_SLOT))
+			zram_free_page(zram, pps->index);
+		zram_slot_write_unlock(zram, pps->index);
+
+		kfree(pps);
+		spin_lock(&zram->slot_free_lock);
+	}
+	spin_unlock(&zram->slot_free_lock);
+};
+
+static void zram_kick_slot_free(struct zram *zram)
+{
+	schedule_work(&zram->slot_free_work);
+}
+
+static void zram_flush_slot_free(struct zram *zram)
+{
+	flush_work(&zram->slot_free_work);
+}
+
+static void zram_init_slot_free(struct zram *zram)
+{
+	spin_lock_init(&zram->slot_free_lock);
+	INIT_LIST_HEAD(&zram->slot_free_list);
+	INIT_WORK(&zram->slot_free_work, async_slot_free);
+}
+
 static void zram_slot_free_notify(struct block_device *bdev,
-				unsigned long index)
+				  unsigned long index)
 {
+	struct zram_pp_slot *pps;
 	struct zram *zram;
 
 	zram = bdev->bd_disk->private_data;
@@ -2328,7 +2371,24 @@ static void zram_slot_free_notify(struct block_device *bdev,
 		return;
 	}
 
-	zram_free_page(zram, index);
+	if (zram_test_flag(zram, index, ZRAM_PP_SLOT))
+		goto out;
+
+	pps = kzalloc(sizeof(*pps), GFP_ATOMIC);
+	if (!pps) {
+		atomic64_inc(&zram->stats.miss_free);
+		goto out;
+	}
+
+	INIT_LIST_HEAD(&pps->entry);
+	pps->index = index;
+	zram_set_flag(zram, index, ZRAM_PP_SLOT);
+	spin_lock(&zram->slot_free_lock);
+	list_add(&pps->entry, &zram->slot_free_list);
+	spin_unlock(&zram->slot_free_lock);
+
+	zram_kick_slot_free(zram);
+out:
 	zram_slot_write_unlock(zram, index);
 }
 
@@ -2473,6 +2533,7 @@ static ssize_t reset_store(struct device *dev,
 
 	/* Make sure all the pending I/O are finished */
 	sync_blockdev(disk->part0);
+	zram_flush_slot_free(zram);
 	zram_reset_device(zram);
 
 	mutex_lock(&disk->open_mutex);
@@ -2618,6 +2679,7 @@ static int zram_add(void)
 	atomic_set(&zram->pp_in_progress, 0);
 	zram_comp_params_reset(zram);
 	comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
+	zram_init_slot_free(zram);
 
 	/* Actual capacity set using sysfs (/sys/block/zram<id>/disksize */
 	set_capacity(zram->disk, 0);
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index b7e250d6fa02..27ca269f4a4e 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -134,5 +134,9 @@ struct zram {
 	struct dentry *debugfs_dir;
 #endif
 	atomic_t pp_in_progress;
+
+	spinlock_t slot_free_lock;
+	struct list_head slot_free_list;
+	struct work_struct slot_free_work;
 };
 #endif
-- 
2.48.1.262.g85cc9f2d1e-goog