drm/i915: optimise i915_gem_object_map() for small objects
We're using this function for ringbuffers and other "small" objects, so
it's worth avoiding an extra malloc()/free() 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).
v5:
change name of local array [Chris Wilson]
Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1463741647-15666-3-git-send-email-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index f504c31..fd3be2b 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2404,7 +2404,8 @@
unsigned long n_pages = obj->base.size >> PAGE_SHIFT;
struct sg_table *sgt = obj->pages;
struct sg_page_iter sg_iter;
- struct page **pages;
+ struct page *stack_pages[32];
+ struct page **pages = stack_pages;
unsigned long i = 0;
void *addr;
@@ -2412,9 +2413,12 @@
if (n_pages == 1)
return kmap(sg_page(sgt->sgl));
- pages = drm_malloc_gfp(n_pages, sizeof(*pages), GFP_TEMPORARY);
- if (!pages)
- return NULL;
+ if (n_pages > ARRAY_SIZE(stack_pages)) {
+ /* Too big for stack -- allocate temporary array instead */
+ pages = drm_malloc_gfp(n_pages, sizeof(*pages), GFP_TEMPORARY);
+ if (!pages)
+ return NULL;
+ }
for_each_sg_page(sgt->sgl, &sg_iter, sgt->nents, 0)
pages[i++] = sg_page_iter_page(&sg_iter);
@@ -2424,7 +2428,8 @@
addr = vmap(pages, n_pages, 0, PAGE_KERNEL);
- drm_free_large(pages);
+ if (pages != stack_pages)
+ drm_free_large(pages);
return addr;
}