[PATCH 15/15] ttm: add support for a module option to disable memcg integration

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

This adds a kconfig and a module option to turn off ttm memcg
integration completely.

When this is used, no object will ever end up using memcg aware
paths.

There is an existing workload that cgroup support might regress,
the systems are setup to allocate 1GB of uncached pages at system
startup to prime the pool, then any further users will take them
from the pool. The current cgroup code might handle that, but
it also may regress, so add an option to ttm to avoid using
memcg for the pool pages.

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 drivers/gpu/drm/Kconfig        |  7 +++++++
 drivers/gpu/drm/ttm/ttm_pool.c | 24 +++++++++++++++++++++---
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index f7ea8e895c0c..4a1501b05e7c 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -239,6 +239,13 @@ config DRM_TTM_HELPER
 	help
 	  Helpers for ttm-based gem objects
 
+config DRM_TTM_MEMCG
+	bool "Enable TTM mem cgroup by default"
+	depends on DRM_TTM
+	depends on MEMCG
+	help
+	  Enable the memcg intergration by default
+
 config DRM_GEM_DMA_HELPER
 	tristate
 	depends on DRM
diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index 1e6da2cc1f06..375858b84fb2 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -118,6 +118,24 @@ static unsigned long page_pool_size;
 MODULE_PARM_DESC(page_pool_size, "Number of pages in the WC/UC/DMA pool per NUMA node");
 module_param(page_pool_size, ulong, 0644);
 
+/*
+ * Don't use the memcg aware lru for pooled pages.
+ *
+ * There are use-cases where for example one application in a cgroup will preallocate 1GB
+ * of uncached pages, and immediately release them into the pool, for other consumers
+ * to use. This use-case could be handled with a proper cgroup hierarchy, but to allow
+ * that use case to continue to operate as-is, add a module option.
+ *
+ * This still stores the pages in the list_lru, it just doesn't use the memcg when
+ * adding/removing them.
+ */
+#define DEFAULT_TTM_MEMCG CONFIG_DRM_TTM_MEMCG
+static bool ttm_memcg = DEFAULT_TTM_MEMCG;
+
+MODULE_PARM_DESC(ttm_memcg, "Allow using cgroups with TTM "
+		 "[default=" __stringify(DEFAULT_TTM_MEMCG) "])");
+module_param(ttm_memcg, bool, 0444);
+
 static unsigned long pool_node_limit[MAX_NUMNODES];
 static atomic_long_t allocated_pages[MAX_NUMNODES];
 
@@ -305,7 +323,7 @@ static void ttm_pool_type_give(struct ttm_pool_type *pt, struct page *p)
 
 	INIT_LIST_HEAD(&p->lru);
 	rcu_read_lock();
-	list_lru_add(&pt->pages, &p->lru, nid, page_memcg_check(p));
+	list_lru_add(&pt->pages, &p->lru, nid, ttm_memcg ? page_memcg_check(p) : NULL);
 	rcu_read_unlock();
 
 	atomic_long_add(num_pages, &allocated_pages[nid]);
@@ -354,7 +372,7 @@ static struct page *ttm_pool_type_take(struct ttm_pool_type *pt, int nid,
 	struct page *page_out = NULL;
 	int ret;
 	struct mem_cgroup *orig_memcg = orig_objcg ? get_mem_cgroup_from_objcg(orig_objcg) : NULL;
-	struct mem_cgroup *memcg = orig_memcg;
+	struct mem_cgroup *memcg = ttm_memcg ? orig_memcg : NULL;
 
 	/*
 	 * Attempt to get a page from the current memcg, but if it hasn't got any in it's level,
@@ -824,7 +842,7 @@ static int __ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
 	bool allow_pools;
 	struct page *p;
 	int r;
-	struct obj_cgroup *objcg = memcg_account ? tt->objcg : NULL;
+	struct obj_cgroup *objcg = (ttm_memcg && memcg_account) ? tt->objcg : NULL;
 
 	WARN_ON(!alloc->remaining_pages || ttm_tt_is_populated(tt));
 	WARN_ON(alloc->dma_addr && !pool->dev);
-- 
2.49.0