[RFC] drm: property: use vzalloc() instead of kvzalloc() for large blobs

[Abhinav Kumar]

For DRM property blobs created by user mode using
drm_property_create_blob(), if the blob value needs to be updated the
only way is to destroy the previous blob and create a new one instead.

For some of the property blobs, if the size of the blob is more
than one page size, kvzalloc() can slow down system as it will first
try to allocate physically contiguous memory but upon failure will
fall back to non-contiguous (vmalloc) allocation.

If the blob property being used is bigger than one page size, in a
heavily loaded system, this causes performance issues because
some of the blobs are updated on a per-frame basis.

To mitigate the performance impact of kvzalloc(), use it only when
the size of allocation is less than a page size when creating property
blobs

Signed-off-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
---
 drivers/gpu/drm/drm_property.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_property.c b/drivers/gpu/drm/drm_property.c
index dfec479830e4..40c2a3142038 100644
--- a/drivers/gpu/drm/drm_property.c
+++ b/drivers/gpu/drm/drm_property.c
@@ -561,7 +561,11 @@ drm_property_create_blob(struct drm_device *dev, size_t length,
 	if (!length || length > INT_MAX - sizeof(struct drm_property_blob))
 		return ERR_PTR(-EINVAL);
 
-	blob = kvzalloc(sizeof(struct drm_property_blob)+length, GFP_KERNEL);
+	if (sizeof(struct drm_property_blob) + length > PAGE_SIZE)
+		blob = vzalloc(sizeof(struct drm_property_blob)+length);
+	else
+		blob = kvzalloc(sizeof(struct drm_property_blob)+length, GFP_KERNEL);
+
 	if (!blob)
 		return ERR_PTR(-ENOMEM);
 
-- 
2.7.4