[RFC PATCH 06/16] drm/ttm: Don't use watermark accounting on shrinkable pools

[Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>]

Clarify the meaning of the ttm_tt pages_limit watermarks as the max
number of pages not accessible by shrinkers, and update accordingly so that
memory allocated by TTM devices that support shrinking is not
accounted against those limits. In particular this means that devices
using the dma_alloc pool will still be using the watermark method.

Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/ttm/ttm_device.c |  3 ++-
 drivers/gpu/drm/ttm/ttm_tt.c     | 43 +++++++++++++++++++-------------
 include/drm/ttm/ttm_pool.h       | 15 +++++++++++
 3 files changed, 42 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
index a3cac42bb456..e0a2be3ed13d 100644
--- a/drivers/gpu/drm/ttm/ttm_device.c
+++ b/drivers/gpu/drm/ttm/ttm_device.c
@@ -168,7 +168,8 @@ long ttm_device_swapout(struct ttm_device *bdev, struct ttm_operation_ctx *ctx,
 	unsigned i;
 	long ret;
 
-	if (reason != TTM_SHRINK_WATERMARK && !bdev->funcs->bo_shrink)
+	if (reason != TTM_SHRINK_WATERMARK &&
+	    (!bdev->funcs->bo_shrink || !ttm_pool_can_shrink(&bdev->pool)))
 		return 0;
 
 	spin_lock(&bdev->lru_lock);
diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index a68c14de0161..771e5f3c2fee 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -54,6 +54,21 @@ module_param_named(dma32_pages_limit, ttm_dma32_pages_limit, ulong, 0644);
 static atomic_long_t ttm_pages_allocated;
 static atomic_long_t ttm_dma32_pages_allocated;
 
+static bool ttm_tt_shrinkable(const struct ttm_device *bdev,
+			      const struct ttm_tt *tt)
+{
+	return !!bdev->funcs->bo_shrink &&
+		ttm_pool_can_shrink(&bdev->pool) &&
+		!(tt->page_flags & TTM_TT_FLAG_EXTERNAL);
+}
+
+static void ttm_tt_mod_allocated(bool dma32, long value)
+{
+	atomic_long_add(value, &ttm_pages_allocated);
+	if (dma32)
+		atomic_long_add(value, &ttm_dma32_pages_allocated);
+}
+
 /*
  * Allocates a ttm structure for the given BO.
  */
@@ -304,12 +319,9 @@ int ttm_tt_populate(struct ttm_device *bdev,
 	if (ttm_tt_is_populated(ttm))
 		return 0;
 
-	if (!(ttm->page_flags & TTM_TT_FLAG_EXTERNAL)) {
-		atomic_long_add(ttm->num_pages, &ttm_pages_allocated);
-		if (bdev->pool.use_dma32)
-			atomic_long_add(ttm->num_pages,
-					&ttm_dma32_pages_allocated);
-	}
+	if (!(ttm->page_flags & TTM_TT_FLAG_EXTERNAL) &&
+	    !ttm_tt_shrinkable(bdev, ttm))
+		ttm_tt_mod_allocated(bdev->pool.use_dma32, ttm->num_pages);
 
 	while (atomic_long_read(&ttm_pages_allocated) > ttm_pages_limit ||
 	       atomic_long_read(&ttm_dma32_pages_allocated) >
@@ -343,12 +355,10 @@ int ttm_tt_populate(struct ttm_device *bdev,
 	return 0;
 
 error:
-	if (!(ttm->page_flags & TTM_TT_FLAG_EXTERNAL)) {
-		atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
-		if (bdev->pool.use_dma32)
-			atomic_long_sub(ttm->num_pages,
-					&ttm_dma32_pages_allocated);
-	}
+	if (!(ttm->page_flags & TTM_TT_FLAG_EXTERNAL) &&
+	    !ttm_tt_shrinkable(bdev, ttm))
+		ttm_tt_mod_allocated(bdev->pool.use_dma32, -(long)ttm->num_pages);
+
 	return ret;
 }
 EXPORT_SYMBOL(ttm_tt_populate);
@@ -363,12 +373,9 @@ void ttm_tt_unpopulate(struct ttm_device *bdev, struct ttm_tt *ttm)
 	else
 		ttm_pool_free(&bdev->pool, ttm);
 
-	if (!(ttm->page_flags & TTM_TT_FLAG_EXTERNAL)) {
-		atomic_long_sub(ttm->num_pages, &ttm_pages_allocated);
-		if (bdev->pool.use_dma32)
-			atomic_long_sub(ttm->num_pages,
-					&ttm_dma32_pages_allocated);
-	}
+	if (!(ttm->page_flags & TTM_TT_FLAG_EXTERNAL) &&
+	    !ttm_tt_shrinkable(bdev, ttm))
+		ttm_tt_mod_allocated(bdev->pool.use_dma32, -(long)ttm->num_pages);
 
 	ttm->page_flags &= ~TTM_TT_FLAG_PRIV_POPULATED;
 }
diff --git a/include/drm/ttm/ttm_pool.h b/include/drm/ttm/ttm_pool.h
index ef09b23d29e3..c1200552892e 100644
--- a/include/drm/ttm/ttm_pool.h
+++ b/include/drm/ttm/ttm_pool.h
@@ -89,4 +89,19 @@ int ttm_pool_debugfs(struct ttm_pool *pool, struct seq_file *m);
 int ttm_pool_mgr_init(unsigned long num_pages);
 void ttm_pool_mgr_fini(void);
 
+/**
+ * ttm_pool_can_shrink - Whether page allocations from this pool are shrinkable
+ * @pool: The pool.
+ *
+ * Return: true if shrinkable, false if not.
+ */
+static inline bool ttm_pool_can_shrink(const struct ttm_pool *pool)
+{
+	/*
+	 * The dma_alloc pool pages can't be inserted into the
+	 * swap cache. Nor can they be split.
+	 */
+	return !pool->use_dma_alloc;
+}
+
 #endif
-- 
2.34.1