[PATCH v2 1/3] dma-buf: heaps: Add deferred-free-helper library code

* [PATCH v2 1/3] dma-buf: heaps: Add deferred-free-helper library code
@ 2021-01-23  3:46 John Stultz
  2021-01-23  3:46 ` [PATCH v2 2/3] dma-buf: system_heap: Add pagepool support to system heap John Stultz
  2021-01-23  3:46 ` [PATCH v2 3/3] dma-buf: system_heap: Add deferred freeing to the " John Stultz
  0 siblings, 2 replies; 6+ messages in thread
From: John Stultz @ 2021-01-23  3:46 UTC (permalink / raw)
  To: lkml
  Cc: John Stultz, Daniel Vetter, Sumit Semwal, Liam Mark,
	Chris Goldsworthy, Laura Abbott, Brian Starkey, Hridya Valsaraju,
	Suren Baghdasaryan, Sandeep Patil, Daniel Mentz, Ørjan Eide,
	Robin Murphy, Ezequiel Garcia, Simon Ser, James Jones,
	linux-media, dri-devel

This patch provides infrastructure for deferring buffer frees.

This is a feature ION provided which when used with some form
of a page pool, provides a nice performance boost in an
allocation microbenchmark. The reason it helps is it allows the
page-zeroing to be done out of the normal allocation/free path,
and pushed off to a kthread.

As not all heaps will find this useful, its implemented as
a optional helper library that heaps can utilize.

Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Liam Mark <lmark@codeaurora.org>
Cc: Chris Goldsworthy <cgoldswo@codeaurora.org>
Cc: Laura Abbott <labbott@kernel.org>
Cc: Brian Starkey <Brian.Starkey@arm.com>
Cc: Hridya Valsaraju <hridya@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sandeep Patil <sspatil@google.com>
Cc: Daniel Mentz <danielmentz@google.com>
Cc: Ørjan Eide <orjan.eide@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Ezequiel Garcia <ezequiel@collabora.com>
Cc: Simon Ser <contact@emersion.fr>
Cc: James Jones <jajones@nvidia.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
v2:
* Fix sleep in atomic issue from using a mutex, by switching
  to a spinlock as Reported-by: kernel test robot <oliver.sang@intel.com>
* Cleanup API to use a reason enum for clarity and add some documentation
  comments as suggested by Suren Baghdasaryan.
---
 drivers/dma-buf/heaps/Kconfig                |   3 +
 drivers/dma-buf/heaps/Makefile               |   1 +
 drivers/dma-buf/heaps/deferred-free-helper.c | 136 +++++++++++++++++++
 drivers/dma-buf/heaps/deferred-free-helper.h |  55 ++++++++
 4 files changed, 195 insertions(+)
 create mode 100644 drivers/dma-buf/heaps/deferred-free-helper.c
 create mode 100644 drivers/dma-buf/heaps/deferred-free-helper.h

diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig
index a5eef06c4226..ecf65204f714 100644
--- a/drivers/dma-buf/heaps/Kconfig
+++ b/drivers/dma-buf/heaps/Kconfig
@@ -1,3 +1,6 @@
+config DMABUF_HEAPS_DEFERRED_FREE
+	bool
+
 config DMABUF_HEAPS_SYSTEM
 	bool "DMA-BUF System Heap"
 	depends on DMABUF_HEAPS
diff --git a/drivers/dma-buf/heaps/Makefile b/drivers/dma-buf/heaps/Makefile
index 974467791032..4e7839875615 100644
--- a/drivers/dma-buf/heaps/Makefile
+++ b/drivers/dma-buf/heaps/Makefile
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_DMABUF_HEAPS_DEFERRED_FREE) += deferred-free-helper.o
 obj-$(CONFIG_DMABUF_HEAPS_SYSTEM)	+= system_heap.o
 obj-$(CONFIG_DMABUF_HEAPS_CMA)		+= cma_heap.o
diff --git a/drivers/dma-buf/heaps/deferred-free-helper.c b/drivers/dma-buf/heaps/deferred-free-helper.c
new file mode 100644
index 000000000000..cf04148167a2
--- /dev/null
+++ b/drivers/dma-buf/heaps/deferred-free-helper.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Deferred dmabuf freeing helper
+ *
+ * Copyright (C) 2020 Linaro, Ltd.
+ *
+ * Based on the ION page pool code
+ * Copyright (C) 2011 Google, Inc.
+ */
+
+#include <linux/freezer.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/swap.h>
+#include <linux/sched/signal.h>
+
+#include "deferred-free-helper.h"
+
+static LIST_HEAD(free_list);
+static size_t list_size;
+wait_queue_head_t freelist_waitqueue;
+struct task_struct *freelist_task;
+static DEFINE_SPINLOCK(free_list_lock);
+
+void deferred_free(struct deferred_freelist_item *item,
+		   void (*free)(struct deferred_freelist_item*,
+				enum df_reason),
+		   size_t size)
+{
+	unsigned long flags;
+
+	INIT_LIST_HEAD(&item->list);
+	item->size = size;
+	item->free = free;
+
+	spin_lock_irqsave(&free_list_lock, flags);
+	list_add(&item->list, &free_list);
+	list_size += size;
+	spin_unlock_irqrestore(&free_list_lock, flags);
+	wake_up(&freelist_waitqueue);
+}
+
+static size_t free_one_item(enum df_reason reason)
+{
+	unsigned long flags;
+	size_t size = 0;
+	struct deferred_freelist_item *item;
+
+	spin_lock_irqsave(&free_list_lock, flags);
+	if (list_empty(&free_list)) {
+		spin_unlock_irqrestore(&free_list_lock, flags);
+		return 0;
+	}
+	item = list_first_entry(&free_list, struct deferred_freelist_item, list);
+	list_del(&item->list);
+	size = item->size;
+	list_size -= size;
+	spin_unlock_irqrestore(&free_list_lock, flags);
+
+	item->free(item, reason);
+	return size;
+}
+
+static unsigned long get_freelist_size(void)
+{
+	unsigned long size;
+	unsigned long flags;
+
+	spin_lock_irqsave(&free_list_lock, flags);
+	size = list_size;
+	spin_unlock_irqrestore(&free_list_lock, flags);
+	return size;
+}
+
+static unsigned long freelist_shrink_count(struct shrinker *shrinker,
+					   struct shrink_control *sc)
+{
+	return get_freelist_size();
+}
+
+static unsigned long freelist_shrink_scan(struct shrinker *shrinker,
+					  struct shrink_control *sc)
+{
+	int total_freed = 0;
+
+	if (sc->nr_to_scan == 0)
+		return 0;
+
+	while (total_freed < sc->nr_to_scan) {
+		int freed = free_one_item(DF_UNDER_PRESSURE);
+
+		if (!freed)
+			break;
+
+		total_freed += freed;
+	}
+
+	return total_freed;
+}
+
+static struct shrinker freelist_shrinker = {
+	.count_objects = freelist_shrink_count,
+	.scan_objects = freelist_shrink_scan,
+	.seeks = DEFAULT_SEEKS,
+	.batch = 0,
+};
+
+static int deferred_free_thread(void *data)
+{
+	while (true) {
+		wait_event_freezable(freelist_waitqueue,
+				     get_freelist_size() > 0);
+
+		free_one_item(DF_NORMAL);
+	}
+
+	return 0;
+}
+
+static int deferred_freelist_init(void)
+{
+	list_size = 0;
+
+	init_waitqueue_head(&freelist_waitqueue);
+	freelist_task = kthread_run(deferred_free_thread, NULL,
+				    "%s", "dmabuf-deferred-free-worker");
+	if (IS_ERR(freelist_task)) {
+		pr_err("%s: creating thread for deferred free failed\n",
+		       __func__);
+		return -1;
+	}
+	sched_set_normal(freelist_task, 19);
+
+	return register_shrinker(&freelist_shrinker);
+}
+device_initcall(deferred_freelist_init);
diff --git a/drivers/dma-buf/heaps/deferred-free-helper.h b/drivers/dma-buf/heaps/deferred-free-helper.h
new file mode 100644
index 000000000000..2c43dd5a3eda
--- /dev/null
+++ b/drivers/dma-buf/heaps/deferred-free-helper.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef DEFERRED_FREE_HELPER_H
+#define DEFERRED_FREE_HELPER_H
+
+/**
+ * df_reason - enum for reason why item was freed
+ *
+ * This provides a reason for why the free funciton was called
+ * on the item. This is useful when deferred_free is used in
+ * combination with a pagepool, so under pressure the page can
+ * be immediately freed.
+ *
+ * DF_NORMAL:         Normal deferred free
+ *
+ * DF_UNDER_PRESSURE: Free was called because the system
+ *                    is under memory pressure. Usually
+ *                    from a shrinker. Avoid allocating
+ *                    memory in the free call, as it may
+ *                    fail.
+ */
+enum df_reason {
+	DF_NORMAL,
+	DF_UNDER_PRESSURE,
+};
+
+/**
+ * deferred_freelist_item - item structure for deferred freelist
+ *
+ * This is to be added to the structure for whatever you want to
+ * defer freeing on.
+ *
+ * @size: size of the item to be freed
+ * @free: function pointer to be called when freeing the item
+ * @list: list entry for the deferred list
+ */
+struct deferred_freelist_item {
+	size_t size;
+	void (*free)(struct deferred_freelist_item *i,
+		     enum df_reason reason);
+	struct list_head list;
+};
+
+/**
+ * deferred_free - call to add item to the deferred free list
+ *
+ * @item: Pointer to deferred_freelist_item field of a structure
+ * @free: Function pointer to the free call
+ * @size: Size of the item to be freed
+ */
+void deferred_free(struct deferred_freelist_item *item,
+		   void (*free)(struct deferred_freelist_item *i,
+				enum df_reason reason),
+		   size_t size);
+#endif
-- 
2.17.1


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