On Mon, Feb 22, 2016 at 03:18:28PM +0000, Dave Gordon wrote:
> Now that we use this function for ringbuffers and other "small" objects,
> it's worth avoiding an extra kmalloc()/kfree() cycle if the page array
> is small enough to put on the stack. Here we've chosen an arbitrary
> cutoff of 32 (4k) pages, which is big enough for a ringbuffer (4 pages)
> or a context image (currently up to 22 pages).
>
> Signed-off-by: Dave Gordon <david.s.gordon@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Alex Dai <yu.dai@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem.c | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 14942cf..effb69b 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2422,6 +2422,7 @@ void *i915_gem_object_vmap_range(struct drm_i915_gem_object *obj,
> unsigned int npages)
> {
> struct sg_page_iter sg_iter;
> + struct page *mypages[32];
Use stack or stack_pages, that's the pattern we've used elsewhere.
Though pages_on_stack would be more in line with the rest of the kernel.
> struct page **pages;
> void *addr;
> int i;
> @@ -2431,10 +2432,16 @@ void *i915_gem_object_vmap_range(struct drm_i915_gem_object *obj,
> return NULL;
> }
>
> - pages = drm_malloc_ab(npages, sizeof(*pages));
> - if (pages == NULL) {
> - DRM_DEBUG_DRIVER("Failed to get space for pages\n");
> - return NULL;
> + if (npages <= ARRAY_SIZE(mypages))
> + pages = mypages;
If one branch requires braces, add them to all.
> + else {
> + pages = kmalloc(npages*sizeof(*pages), GFP_TEMPORARY | __GFP_NOWARN);
drm_malloc_gfp
Otherwise, seems an ok idea. The deepest vmap is the
ioctl/execbuffer/cmdparser to which using a further 256 bytes of stack is
acceptable.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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