[PATCH 18/18] ttm: add support for a module option to disable memcg pool

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

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/ttm/ttm_pool.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index 1e6da2cc1f06..9d84d9991176 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -118,6 +118,21 @@ 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.
+ */
+static bool pool_cgroup = true;
+MODULE_PARM_DESC(pool_cgroup, "Manage pooled memory using cgroups (default: true)");
+module_param(pool_cgroup, bool, 0444);
+
 static unsigned long pool_node_limit[MAX_NUMNODES];
 static atomic_long_t allocated_pages[MAX_NUMNODES];
 
@@ -305,7 +320,7 @@ 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, pool_cgroup ? page_memcg_check(p) : NULL);
 	rcu_read_unlock();
 
 	atomic_long_add(num_pages, &allocated_pages[nid]);
@@ -354,7 +369,7 @@ 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 = pool_cgroup ? orig_memcg : NULL;
 
 	/*
 	 * Attempt to get a page from the current memcg, but if it hasn't got any in it's level,
-- 
2.49.0