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

Christian König <christian.koenig@xxxxxxx> · Wed, 15 Feb 2023 19:30:35 +0100

Am 15.02.23 um 19:12 schrieb Thomas Hellström:
On Wed, 2023-02-15 at 18:42 +0100, Christian König wrote:
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.
You mean the 64K page size, or the whole patch?

The 64K page size. This was an invention from Microsoft to standardize 
GPU handling ~15-20years ago.

It turned out to be a complete shipwreck and by now 2MiB and 1GiB pages 
or just flexible hardware which can handle everything seem to become 
standard.

This is just nonsense spilling in from the
Windows drivers.
Agreed, but IIRC on the last RFC you asked me not to drop the 64K
pages, so that's why they are here. I can remove them if needed.

We could keep it if it's in any way beneficial, but I'm pretty sure I 
must have been drunk to ask for that.

The only reason for keeping them from a performance point of view is
better efficiency on GPUs with 64K page size if not using a coalescing
IOMMU for dma-mapping.

Are any of those still produced? As far as I know neither NVidia, Intel 
nor AMD still assumes that page size in their hardware for quite a while 
now.

Regards,
Christian.


Let me know what you think is best and I'll adjust accordingly.

/Thomas


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]);
   







