[Intel-gfx] [PATCH 2/8] drm/ttm: add TTM_PAGE_FLAG_SHMEM

[Matthew Auld]

Add new flag to indicate special shmem based tt, which can directly
handle swapping itself, and should be visible to some shrinker.

As part of this we should skip the ttm_pages_allocated accounting, since
such tt objects should already be reachable, and potentially reclaimable
by some shrinker, if under memory pressure, and so shouldn't directly
count towards the swap "watermark" level.

We also need to stop touching the page->mapping and page->index for such
objects, like in ttm_tt_add_mapping, since shmem already uses these.
Some drivers seems to depend on the tt mapping/index behaviour for their
own purposes, so directly using shmem tt likely won't be usable there
as-is.

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Cc: Christian König <christian.koenig at amd.com>
---
 drivers/gpu/drm/ttm/ttm_bo_vm.c |  4 ++--
 drivers/gpu/drm/ttm/ttm_tt.c    | 10 +++++-----
 include/drm/ttm/ttm_tt.h        |  1 +
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index f56be5bc0861..e2131c73dcb6 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -346,8 +346,8 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
 			} else if (unlikely(!page)) {
 				break;
 			}
-			page->index = drm_vma_node_start(&bo->base.vma_node) +
-				page_offset;
+			if (!(bo->ttm->page_flags & TTM_PAGE_FLAG_SHMEM))
+				page->index = drm_vma_node_start(&bo->base.vma_node) + page_offset;
 			pfn = page_to_pfn(page);
 		}
 
diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index dae52433beeb..cc4815c1f505 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -293,7 +293,7 @@ static void ttm_tt_add_mapping(struct ttm_device *bdev, struct ttm_tt *ttm)
 {
 	pgoff_t i;
 
-	if (ttm->page_flags & TTM_PAGE_FLAG_SG)
+	if (ttm->page_flags & (TTM_PAGE_FLAG_SG | TTM_PAGE_FLAG_SHMEM))
 		return;
 
 	for (i = 0; i < ttm->num_pages; ++i)
@@ -311,7 +311,7 @@ int ttm_tt_populate(struct ttm_device *bdev,
 	if (ttm_tt_is_populated(ttm))
 		return 0;
 
-	if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
+	if (!(ttm->page_flags & (TTM_PAGE_FLAG_SG | TTM_PAGE_FLAG_SHMEM))) {
 		atomic_long_add(ttm->num_pages, &ttm_pages_allocated);
 		if (bdev->pool.use_dma32)
 			atomic_long_add(ttm->num_pages,
@@ -349,7 +349,7 @@ int ttm_tt_populate(struct ttm_device *bdev,
 	return 0;
 
 error:
-	if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
+	if (!(ttm->page_flags & (TTM_PAGE_FLAG_SG | TTM_PAGE_FLAG_SHMEM))) {
 		atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
 		if (bdev->pool.use_dma32)
 			atomic_long_sub(ttm->num_pages,
@@ -364,7 +364,7 @@ static void ttm_tt_clear_mapping(struct ttm_tt *ttm)
 	pgoff_t i;
 	struct page **page = ttm->pages;
 
-	if (ttm->page_flags & TTM_PAGE_FLAG_SG)
+	if (ttm->page_flags & (TTM_PAGE_FLAG_SG | TTM_PAGE_FLAG_SHMEM))
 		return;
 
 	for (i = 0; i < ttm->num_pages; ++i) {
@@ -384,7 +384,7 @@ void ttm_tt_unpopulate(struct ttm_device *bdev, struct ttm_tt *ttm)
 	else
 		ttm_pool_free(&bdev->pool, ttm);
 
-	if (!(ttm->page_flags & TTM_PAGE_FLAG_SG)) {
+	if (!(ttm->page_flags & (TTM_PAGE_FLAG_SG | TTM_PAGE_FLAG_SHMEM))) {
 		atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
 		if (bdev->pool.use_dma32)
 			atomic_long_sub(ttm->num_pages,
diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
index 89b15d673b22..20d550185065 100644
--- a/include/drm/ttm/ttm_tt.h
+++ b/include/drm/ttm/ttm_tt.h
@@ -42,6 +42,7 @@ struct ttm_operation_ctx;
 #define TTM_PAGE_FLAG_ZERO_ALLOC      (1 << 6)
 #define TTM_PAGE_FLAG_SG              (1 << 8)
 #define TTM_PAGE_FLAG_NO_RETRY	      (1 << 9)
+#define TTM_PAGE_FLAG_SHMEM	      (1 << 10)
 
 #define TTM_PAGE_FLAG_PRIV_POPULATED  (1 << 31)
 
-- 
2.26.3