[RFC][PATCH 4/5] libdrm: reduce number of reallocations in drmModeAtomicAddProperty

[John Stultz]

From: Adrian Salido <salidoa at google.com>

When calling drmModeAtomicAddProperty allocation of memory happens as
needed in increments of 16 elements. This can be very slow if there are
multiple properties to be updated in an Atomic Commit call.

Increase this to as many as can fit in a memory PAGE to avoid having to
reallocate memory too often.

Cc: Emil Velikov <emil.velikov at collabora.com>
Cc: Sean Paul <seanpaul at chromium.org>
Cc: Alistair Strachan <astrachan at google.com>
Cc: Marissa Wall <marissaw at google.com>
Signed-off-by: John Stultz <john.stultz at linaro.org>
---
 xf86drmMode.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/xf86drmMode.c b/xf86drmMode.c
index 8f8633e..c878d9e 100644
--- a/xf86drmMode.c
+++ b/xf86drmMode.c
@@ -1259,7 +1259,7 @@ drm_public drmModeAtomicReqPtr drmModeAtomicDuplicate(drmModeAtomicReqPtr old)
 			return NULL;
 		}
 		memcpy(new->items, old->items,
-		       old->size_items * sizeof(*new->items));
+		       old->cursor * sizeof(*new->items));
 	} else {
 		new->items = NULL;
 	}
@@ -1322,12 +1322,13 @@ drm_public int drmModeAtomicAddProperty(drmModeAtomicReqPtr req,
 		return -EINVAL;
 
 	if (req->cursor >= req->size_items) {
+		const uint32_t item_size_inc = getpagesize() / sizeof(*req->items);
 		drmModeAtomicReqItemPtr new;
 
-		req->size_items += 16;
+		req->size_items += item_size_inc;
 		new = realloc(req->items, req->size_items * sizeof(*req->items));
 		if (!new) {
-			req->size_items -= 16;
+			req->size_items -= item_size_inc;
 			return -ENOMEM;
 		}
 		req->items = new;
-- 
2.7.4