[Mesa-dev] [PATCH 2/2 v2] mesa: Dynamically allocate the matrix stack.

[Eric Anholt]

By allocating and initializing the matrices at context creation, the OS
can't even overcommit the pages.  This saves about 63k (out of 946k) of
maximum memory size according to massif on simulated vc4
glsl-algebraic-add-add-1.  It also means we could potentially relax the
maximum stack sizes, but that should be a separate commit.

v2: Drop redundant Top update, explain why the stack is small at init
    time.
---
 src/mesa/main/matrix.c | 28 ++++++++++++++++++++++++----
 src/mesa/main/mtypes.h |  1 +
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/mesa/main/matrix.c b/src/mesa/main/matrix.c
index 293d50c33595..b30b983f14fd 100644
--- a/src/mesa/main/matrix.c
+++ b/src/mesa/main/matrix.c
@@ -243,6 +243,24 @@ _mesa_PushMatrix( void )
       }
       return;
    }
+   if (stack->Depth + 1 >= stack->StackSize) {
+      unsigned new_stack_size = stack->StackSize * 2;
+      unsigned i;
+      GLmatrix *new_stack = realloc(stack->Stack,
+                                    sizeof(*new_stack) * new_stack_size);
+
+      if (!new_stack) {
+         _mesa_error(ctx, GL_OUT_OF_MEMORY, "glPushMatrix()");
+         return;
+      }
+
+      for (i = stack->StackSize; i < new_stack_size; i++)
+         _math_matrix_ctr(&new_stack[i]);
+
+      stack->Stack = new_stack;
+      stack->StackSize = new_stack_size;
+   }
+
    _math_matrix_copy( &stack->Stack[stack->Depth + 1],
                       &stack->Stack[stack->Depth] );
    stack->Depth++;
@@ -645,9 +663,10 @@ init_matrix_stack( struct gl_matrix_stack *stack,
    stack->Depth = 0;
    stack->MaxDepth = maxDepth;
    stack->DirtyFlag = dirtyFlag;
-   /* The stack */
-   stack->Stack = calloc(maxDepth, sizeof(GLmatrix));
-   for (i = 0; i < maxDepth; i++) {
+   /* The stack will be dynamically resized at glPushMatrix() time */
+   stack->Stack = calloc(1, sizeof(GLmatrix));
+   stack->StackSize = 1;
+   for (i = 0; i < stack->StackSize; i++) {
       _math_matrix_ctr(&stack->Stack[i]);
    }
    stack->Top = stack->Stack;
@@ -665,11 +684,12 @@ static void
 free_matrix_stack( struct gl_matrix_stack *stack )
 {
    GLuint i;
-   for (i = 0; i < stack->MaxDepth; i++) {
+   for (i = 0; i < stack->StackSize; i++) {
       _math_matrix_dtr(&stack->Stack[i]);
    }
    free(stack->Stack);
    stack->Stack = stack->Top = NULL;
+   stack->StackSize = 0;
 }
 
 /*@}*/
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 2647f8fab841..5b02fadf3cd8 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -3990,6 +3990,7 @@ struct gl_matrix_stack
 {
    GLmatrix *Top;      /**< points into Stack */
    GLmatrix *Stack;    /**< array [MaxDepth] of GLmatrix */
+   unsigned StackSize; /**< Number of elements in Stack */
    GLuint Depth;       /**< 0 <= Depth < MaxDepth */
    GLuint MaxDepth;    /**< size of Stack[] array */
    GLuint DirtyFlag;   /**< _NEW_MODELVIEW or _NEW_PROJECTION, for example */
-- 
2.8.1