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

[Suren Baghdasaryan]

Hi John,
Just a couple nits, otherwise looks sane to me.

On Thu, Dec 17, 2020 at 3:06 PM John Stultz <john.stultz@xxxxxxxxxx> wrote:
>
> 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.

I suggest adding some more description for this API and how it can be
used. IIUC there are 2 uses: lazy deferred freeing using kthread, and
object pooling. no_pool parameter I think deserves some explanation
(disallows pooling when system is under memory pressure).

>
> As not all heaps will find this useful, its implemented as
> a optional helper library that heaps can utilize.
>
> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> Cc: Liam Mark <lmark@xxxxxxxxxxxxxx>
> Cc: Chris Goldsworthy <cgoldswo@xxxxxxxxxxxxxx>
> Cc: Laura Abbott <labbott@xxxxxxxxxx>
> Cc: Brian Starkey <Brian.Starkey@xxxxxxx>
> Cc: Hridya Valsaraju <hridya@xxxxxxxxxx>
> Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Cc: Sandeep Patil <sspatil@xxxxxxxxxx>
> Cc: Daniel Mentz <danielmentz@xxxxxxxxxx>
> Cc: Ørjan Eide <orjan.eide@xxxxxxx>
> Cc: Robin Murphy <robin.murphy@xxxxxxx>
> Cc: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
> Cc: Simon Ser <contact@xxxxxxxxxxx>
> Cc: James Jones <jajones@xxxxxxxxxx>
> Cc: linux-media@xxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
> ---
>  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 |  15 ++
>  4 files changed, 155 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..b8f54860454f
> --- /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_MUTEX(free_list_lock);
> +
> +enum {
> +       USE_POOL = 0,
> +       SKIP_POOL = 1,
> +};

This enum is used for a bool parameter. Either make it part of the
public API or eliminate and use bool instead.

> +
> +void deferred_free(struct deferred_freelist_item *item,
> +                  void (*free)(struct deferred_freelist_item*, bool),
> +                  size_t size)
> +{
> +       INIT_LIST_HEAD(&item->list);
> +       item->size = size;
> +       item->free = free;
> +
> +       mutex_lock(&free_list_lock);
> +       list_add(&item->list, &free_list);
> +       list_size += size;
> +       mutex_unlock(&free_list_lock);
> +       wake_up(&freelist_waitqueue);
> +}
> +
> +static size_t free_one_item(bool nopool)
> +{
> +       size_t size = 0;
> +       struct deferred_freelist_item *item;
> +
> +       mutex_lock(&free_list_lock);
> +       if (list_empty(&free_list)) {
> +               mutex_unlock(&free_list_lock);
> +               return 0;
> +       }
> +       item = list_first_entry(&free_list, struct deferred_freelist_item, list);
> +       list_del(&item->list);
> +       size = item->size;
> +       list_size -= size;
> +       mutex_unlock(&free_list_lock);
> +
> +       item->free(item, nopool);
> +       return size;
> +}
> +
> +static unsigned long get_freelist_size(void)
> +{
> +       unsigned long size;
> +
> +       mutex_lock(&free_list_lock);
> +       size = list_size;
> +       mutex_unlock(&free_list_lock);
> +       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(SKIP_POOL);
> +
> +               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(USE_POOL);
> +       }
> +
> +       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..09a2274a897c
> --- /dev/null
> +++ b/drivers/dma-buf/heaps/deferred-free-helper.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef DEFERRED_FREE_HELPER_H
> +#define DEFERRED_FREE_HELPER_H
> +
> +struct deferred_freelist_item {
> +       size_t size;
> +       void (*free)(struct deferred_freelist_item *i, bool no_pool);
> +       struct list_head list;
> +};

I assume deferred_freelist_item gets embedded in a structure that is
actually being freed?

> +
> +void deferred_free(struct deferred_freelist_item *item,
> +                  void (*free)(struct deferred_freelist_item *i, bool no_pool),
> +                  size_t size);
> +#endif
> --
> 2.17.1
>