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

Christian König <christian.koenig@xxxxxxx> · Wed, 12 Apr 2023 16:17:52 +0200

Am 12.04.23 um 11:08 schrieb Daniel Vetter:
On Tue, 11 Apr 2023 at 15:45, Daniel Vetter <daniel@xxxxxxxx> wrote:
On Tue, Apr 11, 2023 at 02:11:18PM +0200, Christian König wrote:
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@xxxxxxxxxxxxxxx>
Reviewed-by: Christian König <christian.koenig@xxxxxxx>
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?
There's some in-flight patches to rework MAX_ORDER and other things in
linux-next, maybe it's recent? If you check out linux-next then you need
to reapply the patch (since sfr reverted it).
So I looked and on ppc64 PMD_SHIFT is defined in terms of
PTE_INDEX_SIZE, which is defined (for book3s) in terms of the variable
__pte_index_size. This is in 6.3 already and seems pretty old.

Ah! I missed that one, thanks.

So revert? Or fixup patch to make this work on ppc?

I think for now just revert or change it so that we check if PMD_SHIFT 
is a constant.

Thomas do you have any quick solution?

Christian.



---
   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

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch









