drm/i915: Replace the array of pages with a scatterlist

Rather than have multiple data structures for describing our page layout
in conjunction with the array of pages, we can migrate all users over to
a scatterlist.

One major advantage, other than unifying the page tracking structures,
this offers is that we replace the vmalloc'ed array (which can be up to
a megabyte in size) with a chain of individual pages which helps reduce
memory pressure.

The disadvantage is that we then do not have a simple array to iterate,
or to access randomly. The common case for this is in the relocation
processing, which will typically fit within a single scatterlist page
and so be almost the same cost as the simple array. For iterating over
the array, the extra function call could be optimised away, but in
reality is an insignificant cost of either binding the pages, or
performing the pwrite/pread.

v2: Fix drm_clflush_sg() to not invoke wbinvd as well! And fix the
trivial compile error from rebasing.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 55 insertions, 24 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 26c8bf9c5fa6..8f001fa155a1 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -411,6 +411,8 @@ i915_gem_shmem_pread(struct drm_device *dev,
         int hit_slowpath = 0;
         int prefaulted = 0;
         int needs_clflush = 0;
+        struct scatterlist *sg;
+        int i;
 
         user_data = (char __user *) (uintptr_t) args->data_ptr;
         remain = args->size;
@@ -439,9 +441,15 @@ i915_gem_shmem_pread(struct drm_device *dev,
 
         offset = args->offset;
 
-        while (remain > 0) {
+        for_each_sg(obj->pages->sgl, sg, obj->pages->nents, i) {
                 struct page *page;
 
+                if (i < offset >> PAGE_SHIFT)
+                        continue;
+
+                if (remain <= 0)
+                        break;
+
                 /* Operation in this page
                  *
                  * shmem_page_offset = offset within page in shmem file
@@ -452,7 +460,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
                 if ((shmem_page_offset + page_length) > PAGE_SIZE)
                         page_length = PAGE_SIZE - shmem_page_offset;
 
-                page = obj->pages[offset >> PAGE_SHIFT];
+                page = sg_page(sg);
                 page_do_bit17_swizzling = obj_do_bit17_swizzling &&
                         (page_to_phys(page) & (1 << 17)) != 0;
 
@@ -731,6 +739,8 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
         int hit_slowpath = 0;
         int needs_clflush_after = 0;
         int needs_clflush_before = 0;
+        int i;
+        struct scatterlist *sg;
 
         user_data = (char __user *) (uintptr_t) args->data_ptr;
         remain = args->size;
@@ -765,10 +775,16 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
         offset = args->offset;
         obj->dirty = 1;
 
-        while (remain > 0) {
+        for_each_sg(obj->pages->sgl, sg, obj->pages->nents, i) {
                 struct page *page;
                 int partial_cacheline_write;
 
+                if (i < offset >> PAGE_SHIFT)
+                        continue;
+
+                if (remain <= 0)
+                        break;
+
                 /* Operation in this page
                  *
                  * shmem_page_offset = offset within page in shmem file
@@ -787,7 +803,7 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
                         ((shmem_page_offset | page_length)
                                 & (boot_cpu_data.x86_clflush_size - 1));
 
-                page = obj->pages[offset >> PAGE_SHIFT];
+                page = sg_page(sg);
                 page_do_bit17_swizzling = obj_do_bit17_swizzling &&
                         (page_to_phys(page) & (1 << 17)) != 0;
 
@@ -1633,6 +1649,7 @@ static void
 i915_gem_object_put_pages_gtt(struct drm_i915_gem_object *obj)
 {
         int page_count = obj->base.size / PAGE_SIZE;
+        struct scatterlist *sg;
         int ret, i;
 
         BUG_ON(obj->madv == __I915_MADV_PURGED);
@@ -1653,19 +1670,21 @@ i915_gem_object_put_pages_gtt(struct drm_i915_gem_object *obj)
         if (obj->madv == I915_MADV_DONTNEED)
                 obj->dirty = 0;
 
-        for (i = 0; i < page_count; i++) {
+        for_each_sg(obj->pages->sgl, sg, page_count, i) {
+                struct page *page = sg_page(sg);
+
                 if (obj->dirty)
-                        set_page_dirty(obj->pages[i]);
+                        set_page_dirty(page);
 
                 if (obj->madv == I915_MADV_WILLNEED)
-                        mark_page_accessed(obj->pages[i]);
+                        mark_page_accessed(page);
 
-                page_cache_release(obj->pages[i]);
+                page_cache_release(page);
         }
         obj->dirty = 0;
 
-        drm_free_large(obj->pages);
-        obj->pages = NULL;
+        sg_free_table(obj->pages);
+        kfree(obj->pages);
 }
 
 static int
@@ -1682,6 +1701,7 @@ i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
                 return -EBUSY;
 
         ops->put_pages(obj);
+        obj->pages = NULL;
 
         list_del(&obj->gtt_list);
         if (i915_gem_object_is_purgeable(obj))
@@ -1739,6 +1759,8 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
         struct drm_i915_private *dev_priv = obj->base.dev->dev_private;
         int page_count, i;
         struct address_space *mapping;
+        struct sg_table *st;
+        struct scatterlist *sg;
         struct page *page;
         gfp_t gfp;
 
@@ -1749,20 +1771,27 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
         BUG_ON(obj->base.read_domains & I915_GEM_GPU_DOMAINS);
         BUG_ON(obj->base.write_domain & I915_GEM_GPU_DOMAINS);
 
-        /* Get the list of pages out of our struct file.  They'll be pinned
-         * at this point until we release them.
-         */
+        st = kmalloc(sizeof(*st), GFP_KERNEL);
+        if (st == NULL)
+                return -ENOMEM;
+
         page_count = obj->base.size / PAGE_SIZE;
-        obj->pages = drm_malloc_ab(page_count, sizeof(struct page *));
-        if (obj->pages == NULL)
+        if (sg_alloc_table(st, page_count, GFP_KERNEL)) {
+                sg_free_table(st);
+                kfree(st);
                 return -ENOMEM;
+        }
 
-        /* Fail silently without starting the shrinker */
+        /* Get the list of pages out of our struct file.  They'll be pinned
+         * at this point until we release them.
+         *
+         * Fail silently without starting the shrinker
+         */
         mapping = obj->base.filp->f_path.dentry->d_inode->i_mapping;
         gfp = mapping_gfp_mask(mapping);
         gfp |= __GFP_NORETRY | __GFP_NOWARN;
         gfp &= ~(__GFP_IO | __GFP_WAIT);
-        for (i = 0; i < page_count; i++) {
+        for_each_sg(st->sgl, sg, page_count, i) {
                 page = shmem_read_mapping_page_gfp(mapping, i, gfp);
                 if (IS_ERR(page)) {
                         i915_gem_purge(dev_priv, page_count);
@@ -1785,20 +1814,20 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
                         gfp &= ~(__GFP_IO | __GFP_WAIT);
                 }
 
-                obj->pages[i] = page;
+                sg_set_page(sg, page, PAGE_SIZE, 0);
         }
 
         if (i915_gem_object_needs_bit17_swizzle(obj))
                 i915_gem_object_do_bit_17_swizzle(obj);
 
+        obj->pages = st;
         return 0;
 
 err_pages:
-        while (i--)
-                page_cache_release(obj->pages[i]);
-
-        drm_free_large(obj->pages);
-        obj->pages = NULL;
+        for_each_sg(st->sgl, sg, i, page_count)
+                page_cache_release(sg_page(sg));
+        sg_free_table(st);
+        kfree(st);
         return PTR_ERR(page);
 }
 
@@ -2981,7 +3010,7 @@ i915_gem_clflush_object(struct drm_i915_gem_object *obj)
 
         trace_i915_gem_object_clflush(obj);
 
-        drm_clflush_pages(obj->pages, obj->base.size / PAGE_SIZE);
+        drm_clflush_sg(obj->pages);
 }
 
 /** Flushes the GTT write domain for the object if it's dirty. */
@@ -3731,6 +3760,8 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
         i915_gem_object_put_pages(obj);
         i915_gem_object_free_mmap_offset(obj);
 
+        BUG_ON(obj->pages);
+
         drm_gem_object_release(&obj->base);
         i915_gem_info_remove_obj(dev_priv, obj->base.size);