Re: [RFC PATCH 07/16] drm/ttm: Reduce the number of used allocation orders for TTM pages

[Christian König <christian.koenig@xxxxxxx>]

Am 15.02.23 um 17:13 schrieb Thomas Hellström:
> When swapping out, we will split multi-order pages both in order to
> move them to the swap-cache and to be able to return memory to the
> swap cache as soon as possible on a page-by-page basis.
> By reducing the page max order to the system PMD size, we can be nicer
> to the system and avoid splitting gigantic pages.


> On top of this we also
> include the 64K page size in the page sizes tried, since that appears to
> be a common size for GPU applications.

Please completely drop that. This is just nonsense spilling in from the 
Windows drivers.

Christian.

> Looking forward to when we might be able to swap out PMD size folios
> without splitting, this will also be a benefit.
>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> ---
>   drivers/gpu/drm/ttm/ttm_pool.c | 58 ++++++++++++++++++++++++++--------
>   1 file changed, 45 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
> index 1cc7591a9542..8787fb6a218b 100644
> --- a/drivers/gpu/drm/ttm/ttm_pool.c
> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
> @@ -31,6 +31,8 @@
>    * cause they are rather slow compared to alloc_pages+map.
>    */
>   
> +#define pr_fmt(fmt) "[TTM POOL] " fmt
> +
>   #include <linux/module.h>
>   #include <linux/dma-mapping.h>
>   #include <linux/debugfs.h>
> @@ -47,6 +49,18 @@
>   
>   #include "ttm_module.h"
>   
> +#define TTM_MAX_ORDER (PMD_SHIFT - PAGE_SHIFT)
> +#define TTM_64K_ORDER (16 - PAGE_SHIFT)
> +#if (TTM_MAX_ORDER < TTM_64K_ORDER)
> +#undef TTM_MAX_ORDER
> +#define TTM_MAX_ORDER TTM_64K_ORDER
> +#endif
> +#if ((MAX_ORDER - 1) < TTM_MAX_ORDER)
> +#undef TTM_MAX_ORDER
> +#define TTM_MAX_ORDER (MAX_ORDER - 1)
> +#endif
> +#define TTM_DIM_ORDER (TTM_MAX_ORDER + 1)
> +
>   /**
>    * struct ttm_pool_dma - Helper object for coherent DMA mappings
>    *
> @@ -65,16 +79,18 @@ 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 ttm_pool_type global_write_combined[TTM_DIM_ORDER];
> +static struct ttm_pool_type global_uncached[TTM_DIM_ORDER];
>   
> -static struct ttm_pool_type global_dma32_write_combined[MAX_ORDER];
> -static struct ttm_pool_type global_dma32_uncached[MAX_ORDER];
> +static struct ttm_pool_type global_dma32_write_combined[TTM_DIM_ORDER];
> +static struct ttm_pool_type global_dma32_uncached[TTM_DIM_ORDER];
>   
>   static spinlock_t shrinker_lock;
>   static struct list_head shrinker_list;
>   static struct shrinker mm_shrinker;
>   
> +static unsigned int ttm_pool_orders[] = {TTM_MAX_ORDER, 0, 0};
> +
>   /* 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,
>   					unsigned int order)
> @@ -400,6 +416,17 @@ static void __ttm_pool_free(struct ttm_pool *pool, struct ttm_tt *tt,
>   	}
>   }
>   
> +static unsigned int ttm_pool_select_order(unsigned int order, pgoff_t num_pages)
> +{
> +	unsigned int *cur_order = ttm_pool_orders;
> +
> +	order = min_t(unsigned int, __fls(num_pages), order);
> +	while (order < *cur_order)
> +		++cur_order;
> +
> +	return *cur_order;
> +}
> +
>   /**
>    * ttm_pool_alloc - Fill a ttm_tt object
>    *
> @@ -439,9 +466,8 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
>   	else
>   		gfp_flags |= GFP_HIGHUSER;
>   
> -	for (order = min_t(unsigned int, MAX_ORDER - 1, __fls(num_pages));
> -	     num_pages;
> -	     order = min_t(unsigned int, order, __fls(num_pages))) {
> +	order = ttm_pool_select_order(ttm_pool_orders[0], num_pages);
> +	for (; num_pages; order = ttm_pool_select_order(order, num_pages)) {
>   		struct ttm_pool_type *pt;
>   
>   		page_caching = tt->caching;
> @@ -558,7 +584,7 @@ void ttm_pool_init(struct ttm_pool *pool, struct device *dev,
>   
>   	if (use_dma_alloc) {
>   		for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
> -			for (j = 0; j < MAX_ORDER; ++j)
> +			for (j = 0; j < TTM_DIM_ORDER; ++j)
>   				ttm_pool_type_init(&pool->caching[i].orders[j],
>   						   pool, i, j);
>   	}
> @@ -578,7 +604,7 @@ void ttm_pool_fini(struct ttm_pool *pool)
>   
>   	if (pool->use_dma_alloc) {
>   		for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
> -			for (j = 0; j < MAX_ORDER; ++j)
> +			for (j = 0; j < TTM_DIM_ORDER; ++j)
>   				ttm_pool_type_fini(&pool->caching[i].orders[j]);
>   	}
>   
> @@ -632,7 +658,7 @@ static void ttm_pool_debugfs_header(struct seq_file *m)
>   	unsigned int i;
>   
>   	seq_puts(m, "\t ");
> -	for (i = 0; i < MAX_ORDER; ++i)
> +	for (i = 0; i < TTM_DIM_ORDER; ++i)
>   		seq_printf(m, " ---%2u---", i);
>   	seq_puts(m, "\n");
>   }
> @@ -643,7 +669,7 @@ static void ttm_pool_debugfs_orders(struct ttm_pool_type *pt,
>   {
>   	unsigned int i;
>   
> -	for (i = 0; i < MAX_ORDER; ++i)
> +	for (i = 0; i < TTM_DIM_ORDER; ++i)
>   		seq_printf(m, " %8u", ttm_pool_type_count(&pt[i]));
>   	seq_puts(m, "\n");
>   }
> @@ -749,10 +775,16 @@ int ttm_pool_mgr_init(unsigned long num_pages)
>   	if (!page_pool_size)
>   		page_pool_size = num_pages;
>   
> +	if (TTM_64K_ORDER < TTM_MAX_ORDER)
> +		ttm_pool_orders[1] = TTM_64K_ORDER;
> +
> +	pr_debug("Used orders are %u %u %u\n", ttm_pool_orders[0],
> +		 ttm_pool_orders[1], ttm_pool_orders[2]);
> +
>   	spin_lock_init(&shrinker_lock);
>   	INIT_LIST_HEAD(&shrinker_list);
>   
> -	for (i = 0; i < MAX_ORDER; ++i) {
> +	for (i = 0; i < TTM_DIM_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);
> @@ -785,7 +817,7 @@ void ttm_pool_mgr_fini(void)
>   {
>   	unsigned int i;
>   
> -	for (i = 0; i < MAX_ORDER; ++i) {
> +	for (i = 0; i < TTM_DIM_ORDER; ++i) {
>   		ttm_pool_type_fini(&global_write_combined[i]);
>   		ttm_pool_type_fini(&global_uncached[i]);
>