[PATCH v2 1/2] drm/ttm: Only allocate huge pages with new flag TTM_PAGE_FLAG_TRANSHUGE

["Michel Dänzer" <michel@daenzer.net>]

From: Michel Dänzer <michel.daenzer@amd.com>

Previously, TTM would always (with CONFIG_TRANSPARENT_HUGEPAGE enabled)
try to allocate huge pages. However, not all drivers can take advantage
of huge pages, but they would incur the overhead for allocating and
freeing them anyway.

Now, drivers which can take advantage of huge pages need to set the new
flag TTM_PAGE_FLAG_TRANSHUGE to get them. Drivers not setting this flag
no longer incur any overhead for allocating or freeing huge pages.

v2:
* Also guard swapping of consecutive pages in ttm_get_pages
* Reword commit log, hopefully clearer now

Cc: stable@vger.kernel.org
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c  |  2 +-
 drivers/gpu/drm/ttm/ttm_page_alloc.c     | 35 +++++++++++++++++-------
 drivers/gpu/drm/ttm/ttm_page_alloc_dma.c |  8 ++++--
 include/drm/ttm/ttm_tt.h                 |  1 +
 4 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index dfd22db13fb1..e03e9e361e2a 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -988,7 +988,7 @@ static struct ttm_tt *amdgpu_ttm_tt_create(struct ttm_buffer_object *bo,
 		return NULL;
 	}
 	gtt->ttm.ttm.func = &amdgpu_backend_func;
-	if (ttm_sg_tt_init(&gtt->ttm, bo, page_flags)) {
+	if (ttm_sg_tt_init(&gtt->ttm, bo, page_flags | TTM_PAGE_FLAG_TRANSHUGE)) {
 		kfree(gtt);
 		return NULL;
 	}
diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc.c b/drivers/gpu/drm/ttm/ttm_page_alloc.c
index f0481b7b60c5..476d668e1cbd 100644
--- a/drivers/gpu/drm/ttm/ttm_page_alloc.c
+++ b/drivers/gpu/drm/ttm/ttm_page_alloc.c
@@ -760,7 +760,7 @@ static void ttm_put_pages(struct page **pages, unsigned npages, int flags,
 {
 	struct ttm_page_pool *pool = ttm_get_pool(flags, false, cstate);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct ttm_page_pool *huge = ttm_get_pool(flags, true, cstate);
+	struct ttm_page_pool *huge = NULL;
 #endif
 	unsigned long irq_flags;
 	unsigned i;
@@ -780,7 +780,8 @@ static void ttm_put_pages(struct page **pages, unsigned npages, int flags,
 			}
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-			if (!(flags & TTM_PAGE_FLAG_DMA32)) {
+			if ((flags & (TTM_PAGE_FLAG_DMA32 | TTM_PAGE_FLAG_TRANSHUGE)) ==
+			    TTM_PAGE_FLAG_TRANSHUGE) {
 				for (j = 0; j < HPAGE_PMD_NR; ++j)
 					if (p++ != pages[i + j])
 					    break;
@@ -805,6 +806,8 @@ static void ttm_put_pages(struct page **pages, unsigned npages, int flags,
 
 	i = 0;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (flags & TTM_PAGE_FLAG_TRANSHUGE)
+		huge = ttm_get_pool(flags, true, cstate);
 	if (huge) {
 		unsigned max_size, n2free;
 
@@ -877,7 +880,7 @@ static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 {
 	struct ttm_page_pool *pool = ttm_get_pool(flags, false, cstate);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	struct ttm_page_pool *huge = ttm_get_pool(flags, true, cstate);
+	struct ttm_page_pool *huge = NULL;
 #endif
 	struct list_head plist;
 	struct page *p = NULL;
@@ -906,7 +909,8 @@ static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 
 		i = 0;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-		if (!(gfp_flags & GFP_DMA32)) {
+		if ((flags & (TTM_PAGE_FLAG_DMA32 | TTM_PAGE_FLAG_TRANSHUGE)) ==
+		    TTM_PAGE_FLAG_TRANSHUGE) {
 			while (npages >= HPAGE_PMD_NR) {
 				gfp_t huge_flags = gfp_flags;
 
@@ -933,9 +937,13 @@ static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 				return -ENOMEM;
 			}
 
-			/* Swap the pages if we detect consecutive order */
-			if (i > first && pages[i - 1] == p - 1)
-				swap(p, pages[i - 1]);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+			if (flags & TTM_PAGE_FLAG_TRANSHUGE) {
+				/* Swap the pages if we detect consecutive order */
+				if (i > first && pages[i - 1] == p - 1)
+					swap(p, pages[i - 1]);
+			}
+#endif
 
 			pages[i++] = p;
 			--npages;
@@ -946,6 +954,8 @@ static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 	count = 0;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (flags & TTM_PAGE_FLAG_TRANSHUGE)
+		huge = ttm_get_pool(flags, true, cstate);
 	if (huge && npages >= HPAGE_PMD_NR) {
 		INIT_LIST_HEAD(&plist);
 		ttm_page_pool_get_pages(huge, &plist, flags, cstate,
@@ -969,9 +979,14 @@ static int ttm_get_pages(struct page **pages, unsigned npages, int flags,
 	list_for_each_entry(p, &plist, lru) {
 		struct page *tmp = p;
 
-		/* Swap the pages if we detect consecutive order */
-		if (count > first && pages[count - 1] == tmp - 1)
-			swap(tmp, pages[count - 1]);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+		if (flags & TTM_PAGE_FLAG_TRANSHUGE) {
+			/* Swap the pages if we detect consecutive order */
+			if (count > first && pages[count - 1] == tmp - 1)
+				swap(tmp, pages[count - 1]);
+		}
+#endif
+
 		pages[count++] = tmp;
 	}
 
diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
index 8a25d1974385..291b04213ec5 100644
--- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
+++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
@@ -949,7 +949,8 @@ int ttm_dma_populate(struct ttm_dma_tt *ttm_dma, struct device *dev,
 	type = ttm_to_type(ttm->page_flags, ttm->caching_state);
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (ttm->page_flags & TTM_PAGE_FLAG_DMA32)
+	if ((ttm->page_flags & (TTM_PAGE_FLAG_DMA32 | TTM_PAGE_FLAG_TRANSHUGE))
+	    != TTM_PAGE_FLAG_TRANSHUGE)
 		goto skip_huge;
 
 	pool = ttm_dma_find_pool(dev, type | IS_HUGE);
@@ -1035,7 +1036,7 @@ void ttm_dma_unpopulate(struct ttm_dma_tt *ttm_dma, struct device *dev)
 {
 	struct ttm_tt *ttm = &ttm_dma->ttm;
 	struct ttm_mem_global *mem_glob = ttm->bdev->glob->mem_glob;
-	struct dma_pool *pool;
+	struct dma_pool *pool = NULL;
 	struct dma_page *d_page, *next;
 	enum pool_type type;
 	bool is_cached = false;
@@ -1045,7 +1046,8 @@ void ttm_dma_unpopulate(struct ttm_dma_tt *ttm_dma, struct device *dev)
 	type = ttm_to_type(ttm->page_flags, ttm->caching_state);
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	pool = ttm_dma_find_pool(dev, type | IS_HUGE);
+	if (ttm->page_flags & TTM_PAGE_FLAG_TRANSHUGE)
+		pool = ttm_dma_find_pool(dev, type | IS_HUGE);
 	if (pool) {
 		count = 0;
 		list_for_each_entry_safe(d_page, next, &ttm_dma->pages_list,
diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
index c0e928abf592..c7d2120f0362 100644
--- a/include/drm/ttm/ttm_tt.h
+++ b/include/drm/ttm/ttm_tt.h
@@ -41,6 +41,7 @@ struct ttm_operation_ctx;
 #define TTM_PAGE_FLAG_DMA32           (1 << 7)
 #define TTM_PAGE_FLAG_SG              (1 << 8)
 #define TTM_PAGE_FLAG_NO_RETRY	      (1 << 9)
+#define TTM_PAGE_FLAG_TRANSHUGE       (1 << 10)
 
 enum ttm_caching_state {
 	tt_uncached,
-- 
2.17.0