Re: [Intel-gfx] [PATCH RESEND v3 2/3] drm/ttm: Reduce the number of used allocation orders for TTM pages

["Christian König" <christian.koenig@amd.com>]

Am 11.04.23 um 11:51 schrieb Daniel Vetter:
> On Tue, Apr 04, 2023 at 10:06:49PM +0200, Thomas Hellström wrote:
>> 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.
>> Reduce the page max order to the system PMD size, as we can then be nicer
>> to the system and avoid splitting gigantic pages.
>>
>> Looking forward to when we might be able to swap out PMD size folios
>> without splitting, this will also be a benefit.
>>
>> v2:
>> - Include all orders up to the PMD size (Christian König)
>> v3:
>> - Avoid compilation errors for architectures with special PFN_SHIFTs
>>
>> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> Reviewed-by: Christian König <christian.koenig@amd.com>
> Apparently this fails on ppc build testing. Please supply build fix asap
> (or I guess we need to revert). I'm kinda not clear why this only showed
> up when I merged the drm-misc-next pr into drm-next ...

I'm really wondering this as well. It looks like PMD_SHIFT isn't a 
constant on this particular platform.

But from what I can find in the upstream 6.2 kernel PMD_SHIFT always 
seems to be a constant.

So how exactly can that here break?

Christian.

> -Daniel
>
>> ---
>>   drivers/gpu/drm/ttm/ttm_pool.c | 30 +++++++++++++++++++-----------
>>   1 file changed, 19 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
>> index dfce896c4bae..18c342a919a2 100644
>> --- a/drivers/gpu/drm/ttm/ttm_pool.c
>> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
>> @@ -47,6 +47,11 @@
>>   
>>   #include "ttm_module.h"
>>   
>> +#define TTM_MAX_ORDER (PMD_SHIFT - PAGE_SHIFT)
>> +#define __TTM_DIM_ORDER (TTM_MAX_ORDER + 1)
>> +/* Some architectures have a weird PMD_SHIFT */
>> +#define TTM_DIM_ORDER (__TTM_DIM_ORDER <= MAX_ORDER ? __TTM_DIM_ORDER : MAX_ORDER)
>> +
>>   /**
>>    * struct ttm_pool_dma - Helper object for coherent DMA mappings
>>    *
>> @@ -65,11 +70,11 @@ 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;
>> @@ -444,7 +449,7 @@ 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));
>> +	for (order = min_t(unsigned int, TTM_MAX_ORDER, __fls(num_pages));
>>   	     num_pages;
>>   	     order = min_t(unsigned int, order, __fls(num_pages))) {
>>   		struct ttm_pool_type *pt;
>> @@ -563,7 +568,7 @@ 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);
>>   	}
>> @@ -583,7 +588,7 @@ 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]);
>>   	}
>>   
>> @@ -637,7 +642,7 @@ 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");
>>   }
>> @@ -648,7 +653,7 @@ 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");
>>   }
>> @@ -751,13 +756,16 @@ int ttm_pool_mgr_init(unsigned long num_pages)
>>   {
>>   	unsigned int i;
>>   
>> +	BUILD_BUG_ON(TTM_DIM_ORDER > MAX_ORDER);
>> +	BUILD_BUG_ON(TTM_DIM_ORDER < 1);
>> +
>>   	if (!page_pool_size)
>>   		page_pool_size = num_pages;
>>   
>>   	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);
>> @@ -790,7 +798,7 @@ 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]);
>>   
>> -- 
>> 2.39.2
>>