Re: [RFC][PATCH v6 4/7] drm: ttm_pool: Rework ttm_pool to use drm_page_pool

[Christian König <christian.koenig@xxxxxxx>]

Am 05.02.21 um 09:06 schrieb John Stultz:
> This patch reworks the ttm_pool logic to utilize the recently
> added drm_page_pool code.
>
> Basically all the ttm_pool_type structures are replaced with
> drm_page_pool pointers, and since the drm_page_pool logic has
> its own shrinker, we can remove all of the ttm_pool shrinker
> logic.
>
> NOTE: There is one mismatch in the interfaces I'm not totally
> happy with. The ttm_pool tracks all of its pooled pages across
> a number of different pools, and tries to keep this size under
> the specified page_pool_size value. With the drm_page_pool,
> there may other users, however there is still one global
> shrinker list of pools. So we can't easily reduce the ttm
> pool under the ttm specified size without potentially doing
> a lot of shrinking to other non-ttm pools. So either we can:
>    1) Try to split it so each user of drm_page_pools manages its
>       own pool shrinking.
>    2) Push the max value into the drm_page_pool, and have it
>       manage shrinking to fit under that global max. Then share
>       those size/max values out so the ttm_pool debug output
>       can have more context.
>
> I've taken the second path in this patch set, but wanted to call
> it out so folks could look closely.

Option 3: Move the debugging code into the drm_page_pool as well.

I strong think that will be a hard requirement from Daniel for 
upstreaming this.

Christian.

> Thoughts would be greatly appreciated here!
>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Cc: Christian Koenig <christian.koenig@xxxxxxx>
> 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/gpu/drm/Kconfig        |   1 +
>   drivers/gpu/drm/ttm/ttm_pool.c | 199 +++++++--------------------------
>   include/drm/ttm/ttm_pool.h     |  23 +---
>   3 files changed, 41 insertions(+), 182 deletions(-)
>
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index d16bf340ed2e..d427abefabfb 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -181,6 +181,7 @@ config DRM_PAGE_POOL
>   config DRM_TTM
>   	tristate
>   	depends on DRM && MMU
> +	select DRM_PAGE_POOL
>   	help
>   	  GPU memory management subsystem for devices with multiple
>   	  GPU memory types. Will be enabled automatically if a device driver
> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
> index eca36678f967..dbbaf55ca5df 100644
> --- a/drivers/gpu/drm/ttm/ttm_pool.c
> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
> @@ -37,6 +37,7 @@
>   #ifdef CONFIG_X86
>   #include <asm/set_memory.h>
>   #endif
> +#include <drm/page_pool.h>
>   #include <drm/ttm/ttm_pool.h>
>   #include <drm/ttm/ttm_bo_driver.h>
>   #include <drm/ttm/ttm_tt.h>
> @@ -63,15 +64,13 @@ module_param(page_pool_size, ulong, 0644);
>   
>   static atomic_long_t allocated_pages;
>   
> -static struct ttm_pool_type global_write_combined[MAX_ORDER];
> -static struct ttm_pool_type global_uncached[MAX_ORDER];
> +static struct drm_page_pool *global_write_combined[MAX_ORDER];
> +static struct drm_page_pool *global_uncached[MAX_ORDER];
>   
> -static struct ttm_pool_type global_dma32_write_combined[MAX_ORDER];
> -static struct ttm_pool_type global_dma32_uncached[MAX_ORDER];
> +static struct drm_page_pool *global_dma32_write_combined[MAX_ORDER];
> +static struct drm_page_pool *global_dma32_uncached[MAX_ORDER];
>   
>   static struct mutex shrinker_lock;
> -static struct list_head shrinker_list;
> -static struct shrinker mm_shrinker;
>   
>   /* Allocate pages of size 1 << order with the given gfp_flags */
>   static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t gfp_flags,
> @@ -223,79 +222,26 @@ static void ttm_pool_unmap(struct ttm_pool *pool, dma_addr_t dma_addr,
>   		       DMA_BIDIRECTIONAL);
>   }
>   
> -/* Give pages into a specific pool_type */
> -static void ttm_pool_type_give(struct ttm_pool_type *pt, struct page *p)
> -{
> -	spin_lock(&pt->lock);
> -	list_add(&p->lru, &pt->pages);
> -	spin_unlock(&pt->lock);
> -	atomic_long_add(1 << pt->order, &allocated_pages);
> -}
> -
> -/* Take pages from a specific pool_type, return NULL when nothing available */
> -static struct page *ttm_pool_type_take(struct ttm_pool_type *pt)
> -{
> -	struct page *p;
> -
> -	spin_lock(&pt->lock);
> -	p = list_first_entry_or_null(&pt->pages, typeof(*p), lru);
> -	if (p) {
> -		atomic_long_sub(1 << pt->order, &allocated_pages);
> -		list_del(&p->lru);
> -	}
> -	spin_unlock(&pt->lock);
> -
> -	return p;
> -}
> -
> -/* Initialize and add a pool type to the global shrinker list */
> -static void ttm_pool_type_init(struct ttm_pool_type *pt, struct ttm_pool *pool,
> -			       enum ttm_caching caching, unsigned int order)
> -{
> -	pt->pool = pool;
> -	pt->caching = caching;
> -	pt->order = order;
> -	spin_lock_init(&pt->lock);
> -	INIT_LIST_HEAD(&pt->pages);
> -
> -	mutex_lock(&shrinker_lock);
> -	list_add_tail(&pt->shrinker_list, &shrinker_list);
> -	mutex_unlock(&shrinker_lock);
> -}
> -
> -/* Remove a pool_type from the global shrinker list and free all pages */
> -static void ttm_pool_type_fini(struct ttm_pool_type *pt)
> -{
> -	struct page *p, *tmp;
> -
> -	mutex_lock(&shrinker_lock);
> -	list_del(&pt->shrinker_list);
> -	mutex_unlock(&shrinker_lock);
> -
> -	list_for_each_entry_safe(p, tmp, &pt->pages, lru)
> -		ttm_pool_free_page(p, pt->order);
> -}
> -
>   /* Return the pool_type to use for the given caching and order */
> -static struct ttm_pool_type *ttm_pool_select_type(struct ttm_pool *pool,
> +static struct drm_page_pool *ttm_pool_select_type(struct ttm_pool *pool,
>   						  enum ttm_caching caching,
>   						  unsigned int order)
>   {
>   	if (pool->use_dma_alloc)
> -		return &pool->caching[caching].orders[order];
> +		return pool->caching[caching].orders[order];
>   
>   #ifdef CONFIG_X86
>   	switch (caching) {
>   	case ttm_write_combined:
>   		if (pool->use_dma32)
> -			return &global_dma32_write_combined[order];
> +			return global_dma32_write_combined[order];
>   
> -		return &global_write_combined[order];
> +		return global_write_combined[order];
>   	case ttm_uncached:
>   		if (pool->use_dma32)
> -			return &global_dma32_uncached[order];
> +			return global_dma32_uncached[order];
>   
> -		return &global_uncached[order];
> +		return global_uncached[order];
>   	default:
>   		break;
>   	}
> @@ -304,30 +250,6 @@ static struct ttm_pool_type *ttm_pool_select_type(struct ttm_pool *pool,
>   	return NULL;
>   }
>   
> -/* Free pages using the global shrinker list */
> -static unsigned int ttm_pool_shrink(void)
> -{
> -	struct ttm_pool_type *pt;
> -	unsigned int num_freed;
> -	struct page *p;
> -
> -	mutex_lock(&shrinker_lock);
> -	pt = list_first_entry(&shrinker_list, typeof(*pt), shrinker_list);
> -
> -	p = ttm_pool_type_take(pt);
> -	if (p) {
> -		ttm_pool_free_page(p, pt->order);
> -		num_freed = 1 << pt->order;
> -	} else {
> -		num_freed = 0;
> -	}
> -
> -	list_move_tail(&pt->shrinker_list, &shrinker_list);
> -	mutex_unlock(&shrinker_lock);
> -
> -	return num_freed;
> -}
> -
>   /* Return the allocation order based for a page */
>   static unsigned int ttm_pool_page_order(struct ttm_pool *pool, struct page *p)
>   {
> @@ -377,10 +299,10 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
>   	for (order = min(MAX_ORDER - 1UL, __fls(num_pages)); num_pages;
>   	     order = min_t(unsigned int, order, __fls(num_pages))) {
>   		bool apply_caching = false;
> -		struct ttm_pool_type *pt;
> +		struct drm_page_pool *pt;
>   
>   		pt = ttm_pool_select_type(pool, tt->caching, order);
> -		p = pt ? ttm_pool_type_take(pt) : NULL;
> +		p = pt ? drm_page_pool_fetch(pt) : NULL;
>   		if (p) {
>   			apply_caching = true;
>   		} else {
> @@ -462,7 +384,7 @@ void ttm_pool_free(struct ttm_pool *pool, struct ttm_tt *tt)
>   	for (i = 0; i < tt->num_pages; ) {
>   		struct page *p = tt->pages[i];
>   		unsigned int order, num_pages;
> -		struct ttm_pool_type *pt;
> +		struct drm_page_pool *pt;
>   
>   		order = ttm_pool_page_order(pool, p);
>   		num_pages = 1ULL << order;
> @@ -473,15 +395,12 @@ void ttm_pool_free(struct ttm_pool *pool, struct ttm_tt *tt)
>   
>   		pt = ttm_pool_select_type(pool, tt->caching, order);
>   		if (pt)
> -			ttm_pool_type_give(pt, tt->pages[i]);
> +			drm_page_pool_add(pt, tt->pages[i]);
>   		else
>   			ttm_pool_free_page(tt->pages[i], order);
>   
>   		i += num_pages;
>   	}
> -
> -	while (atomic_long_read(&allocated_pages) > page_pool_size)
> -		ttm_pool_shrink();
>   }
>   EXPORT_SYMBOL(ttm_pool_free);
>   
> @@ -508,8 +427,8 @@ void ttm_pool_init(struct ttm_pool *pool, struct device *dev,
>   
>   	for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
>   		for (j = 0; j < MAX_ORDER; ++j)
> -			ttm_pool_type_init(&pool->caching[i].orders[j],
> -					   pool, i, j);
> +			pool->caching[i].orders[j] = drm_page_pool_create(j,
> +							ttm_pool_free_page);
>   }
>   
>   /**
> @@ -526,33 +445,18 @@ void ttm_pool_fini(struct ttm_pool *pool)
>   
>   	for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
>   		for (j = 0; j < MAX_ORDER; ++j)
> -			ttm_pool_type_fini(&pool->caching[i].orders[j]);
> +			drm_page_pool_destroy(pool->caching[i].orders[j]);
>   }
>   
>   #ifdef CONFIG_DEBUG_FS
> -/* Count the number of pages available in a pool_type */
> -static unsigned int ttm_pool_type_count(struct ttm_pool_type *pt)
> -{
> -	unsigned int count = 0;
> -	struct page *p;
> -
> -	spin_lock(&pt->lock);
> -	/* Only used for debugfs, the overhead doesn't matter */
> -	list_for_each_entry(p, &pt->pages, lru)
> -		++count;
> -	spin_unlock(&pt->lock);
> -
> -	return count;
> -}
> -
>   /* Dump information about the different pool types */
> -static void ttm_pool_debugfs_orders(struct ttm_pool_type *pt,
> +static void ttm_pool_debugfs_orders(struct drm_page_pool **pt,
>   				    struct seq_file *m)
>   {
>   	unsigned int i;
>   
>   	for (i = 0; i < MAX_ORDER; ++i)
> -		seq_printf(m, " %8u", ttm_pool_type_count(&pt[i]));
> +		seq_printf(m, " %8u", drm_page_pool_get_size(pt[i]));
>   	seq_puts(m, "\n");
>   }
>   
> @@ -602,7 +506,10 @@ int ttm_pool_debugfs(struct ttm_pool *pool, struct seq_file *m)
>   	}
>   
>   	seq_printf(m, "\ntotal\t: %8lu of %8lu\n",
> -		   atomic_long_read(&allocated_pages), page_pool_size);
> +		   atomic_long_read(&allocated_pages),
> +		   drm_page_pool_get_max());
> +	seq_printf(m, "(%8lu in non-ttm pools)\n", drm_page_pool_get_total() -
> +					atomic_long_read(&allocated_pages));
>   
>   	mutex_unlock(&shrinker_lock);
>   
> @@ -612,28 +519,6 @@ EXPORT_SYMBOL(ttm_pool_debugfs);
>   
>   #endif
>   
> -/* As long as pages are available make sure to release at least one */
> -static unsigned long ttm_pool_shrinker_scan(struct shrinker *shrink,
> -					    struct shrink_control *sc)
> -{
> -	unsigned long num_freed = 0;
> -
> -	do
> -		num_freed += ttm_pool_shrink();
> -	while (!num_freed && atomic_long_read(&allocated_pages));
> -
> -	return num_freed;
> -}
> -
> -/* Return the number of pages available or SHRINK_EMPTY if we have none */
> -static unsigned long ttm_pool_shrinker_count(struct shrinker *shrink,
> -					     struct shrink_control *sc)
> -{
> -	unsigned long num_pages = atomic_long_read(&allocated_pages);
> -
> -	return num_pages ? num_pages : SHRINK_EMPTY;
> -}
> -
>   /**
>    * ttm_pool_mgr_init - Initialize globals
>    *
> @@ -648,24 +533,21 @@ int ttm_pool_mgr_init(unsigned long num_pages)
>   	if (!page_pool_size)
>   		page_pool_size = num_pages;
>   
> +	drm_page_pool_set_max(page_pool_size);
> +
>   	mutex_init(&shrinker_lock);
> -	INIT_LIST_HEAD(&shrinker_list);
>   
>   	for (i = 0; i < MAX_ORDER; ++i) {
> -		ttm_pool_type_init(&global_write_combined[i], NULL,
> -				   ttm_write_combined, i);
> -		ttm_pool_type_init(&global_uncached[i], NULL, ttm_uncached, i);
> -
> -		ttm_pool_type_init(&global_dma32_write_combined[i], NULL,
> -				   ttm_write_combined, i);
> -		ttm_pool_type_init(&global_dma32_uncached[i], NULL,
> -				   ttm_uncached, i);
> +		global_write_combined[i] = drm_page_pool_create(i,
> +							ttm_pool_free_page);
> +		global_uncached[i] = drm_page_pool_create(i,
> +							ttm_pool_free_page);
> +		global_dma32_write_combined[i] = drm_page_pool_create(i,
> +							ttm_pool_free_page);
> +		global_dma32_uncached[i] = drm_page_pool_create(i,
> +							ttm_pool_free_page);
>   	}
> -
> -	mm_shrinker.count_objects = ttm_pool_shrinker_count;
> -	mm_shrinker.scan_objects = ttm_pool_shrinker_scan;
> -	mm_shrinker.seeks = 1;
> -	return register_shrinker(&mm_shrinker);
> +	return 0;
>   }
>   
>   /**
> @@ -678,13 +560,10 @@ void ttm_pool_mgr_fini(void)
>   	unsigned int i;
>   
>   	for (i = 0; i < MAX_ORDER; ++i) {
> -		ttm_pool_type_fini(&global_write_combined[i]);
> -		ttm_pool_type_fini(&global_uncached[i]);
> +		drm_page_pool_destroy(global_write_combined[i]);
> +		drm_page_pool_destroy(global_uncached[i]);
>   
> -		ttm_pool_type_fini(&global_dma32_write_combined[i]);
> -		ttm_pool_type_fini(&global_dma32_uncached[i]);
> +		drm_page_pool_destroy(global_dma32_write_combined[i]);
> +		drm_page_pool_destroy(global_dma32_uncached[i]);
>   	}
> -
> -	unregister_shrinker(&mm_shrinker);
> -	WARN_ON(!list_empty(&shrinker_list));
>   }
> diff --git a/include/drm/ttm/ttm_pool.h b/include/drm/ttm/ttm_pool.h
> index 4321728bdd11..460ab232fd22 100644
> --- a/include/drm/ttm/ttm_pool.h
> +++ b/include/drm/ttm/ttm_pool.h
> @@ -36,27 +36,6 @@ struct ttm_tt;
>   struct ttm_pool;
>   struct ttm_operation_ctx;
>   
> -/**
> - * ttm_pool_type - Pool for a certain memory type
> - *
> - * @pool: the pool we belong to, might be NULL for the global ones
> - * @order: the allocation order our pages have
> - * @caching: the caching type our pages have
> - * @shrinker_list: our place on the global shrinker list
> - * @lock: protection of the page list
> - * @pages: the list of pages in the pool
> - */
> -struct ttm_pool_type {
> -	struct ttm_pool *pool;
> -	unsigned int order;
> -	enum ttm_caching caching;
> -
> -	struct list_head shrinker_list;
> -
> -	spinlock_t lock;
> -	struct list_head pages;
> -};
> -
>   /**
>    * ttm_pool - Pool for all caching and orders
>    *
> @@ -71,7 +50,7 @@ struct ttm_pool {
>   	bool use_dma32;
>   
>   	struct {
> -		struct ttm_pool_type orders[MAX_ORDER];
> +		struct drm_page_pool *orders[MAX_ORDER];
>   	} caching[TTM_NUM_CACHING_TYPES];
>   };
>