drm/i915: Truncate the shmem backing pages on purge

shmfs doesn't actually implement i_ops->truncate() so we were not
immedatiately releasing the backing pages when shrinking the gfx cache
under OOM. Instead use a combination of truncate_inode_pages() and
i_ops->truncate_range() as is used by shmem_delete_inode().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>

1 files changed, 9 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 8f3e0c10c080..41306217bd7a 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1505,9 +1505,16 @@ i915_gem_object_truncate(struct drm_gem_object *obj)
         struct drm_i915_gem_object *obj_priv = to_intel_bo(obj);
         struct inode *inode;
 
+        /* Our goal here is to return as much of the memory as
+         * is possible back to the system as we are called from OOM.
+         * To do this we must instruct the shmfs to drop all of its
+         * backing pages, *now*. Here we mirror the actions taken
+         * when by shmem_delete_inode() to release the backing store.
+         */
         inode = obj->filp->f_path.dentry->d_inode;
-        if (inode->i_op->truncate)
-                inode->i_op->truncate (inode);
+        truncate_inode_pages(inode->i_mapping, 0);
+        if (inode->i_op->truncate_range)
+                inode->i_op->truncate_range(inode, 0, (loff_t)-1);
 
         obj_priv->madv = __I915_MADV_PURGED;
 }