On 20/12/2016 14:14, Chris Wilson wrote:
On Tue, Dec 20, 2016 at 01:42:47PM +0000, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Rather than freeing and re-allocating the pages when DMA mapping
in large chunks fails, we can just rebuild the sg table with no
coalescing.
You are freeing and reallocating the pages - I thought you meant the
sg_table. The cost for recovering the shmemfs after allocation/swapin
already performed in the first pass should be a look up in the radix tree.
Not worrisome.
Maybe not, but looks a bit unsightly to me. This is simple enough and
one re-allocation less. From both pages and sg entries, to just the sg
entries.
Also change back the page counter to unsigned int because that
is what the sg API supports.
Rather go the other way and start reporting an error when we overflow.
Being strict all page_counts should be u64. :|
As I wrote in the other thread, that's already in
i915_gem_object_create. Added there at the time when I spotted the
sg_alloc_table unsigned int business.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
Only compile tested!
---
drivers/gpu/drm/i915/i915_gem.c | 40 ++++++++++++++++++++++++++++++----------
1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 5275f6248ce3..e73f9f5a5d23 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2340,12 +2340,36 @@ static void i915_sg_trim(struct sg_table *orig_st)
*orig_st = new_st;
}
+static void i915_sg_uncoalesce(struct sg_table *orig_st, unsigned long nents)
+{
+ struct sg_table new_st;
+ struct scatterlist *new_sg;
+ struct sgt_iter sgt_iter;
+ struct page *page;
+
+ if (sg_alloc_table(&new_st, nents, GFP_KERNEL))
+ return;
I was hoping for a way to use the pages already allocated. Feels
possible, just reversing the chain and walking backwards will be fun.
For a rainy day as you said. :)
+ new_sg = new_st.sgl;
+ for_each_sgt_page(page, sgt_iter, orig_st) {
+ sg_set_page(new_sg, page, PAGE_SIZE, 0);
+ /* called before being DMA mapped, no need to copy sg->dma_* */
+ new_sg = sg_next(new_sg);
+ }
+
+ GEM_BUG_ON(new_sg); /* Should walk exactly nents and hit the end */
+
+ sg_free_table(orig_st);
+
+ *orig_st = new_st;
+}
Regards,
Tvrtko
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