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drm/i915: Use pagecache write to prepopulate shmemfs from pwrite-ioctl

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Before we instantiate/pin the backing store for our use, we
can prepopulate the shmemfs filp efficiently using a write into the
pagecache. We avoid the penalty of instantiating all the pages, important
if the user is just writing to a few and never uses the object on the GPU,
and using a direct write into shmemfs allows it to avoid the cost of
retrieving a page (mostly the clear-before-use, but in theory we could
curtail swapin) before it is overwritten.

This can be extended later to provide additional specialisation for
other backends (other than shmemfs). For now it provides a defense
against very large write-only allocations from exhausting all of system
memory.

v2: Smelling fixes.

Fixes: fe115628d5 ("drm/i915: Implement pwrite without struct-mutex")
References: https://bugs.freedesktop.org/show_bug.cgi?id=99107
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: <stable@vger.kernel.org> # v4.10+
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170307120338.7277-2-chris@chris-wilson.co.uk
(cherry picked from commit 7c55e2c577)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
This commit is contained in:
Chris Wilson 2017-03-07 12:03:38 +00:00 committed by Jani Nikula
parent 0d9dc306e1
commit 4e6fdafa7a
2 changed files with 81 additions and 0 deletions
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78
drivers/gpu/drm/i915/i915_gem.c
View file

@ -1434,6 +1434,12 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
trace_i915_gem_object_pwrite(obj, args->offset, args->size);
ret = -ENODEV;
if (obj->ops->pwrite)
ret = obj->ops->pwrite(obj, args);
if (ret != -ENODEV)
goto err;
ret = i915_gem_object_wait(obj,
I915_WAIT_INTERRUPTIBLE |
I915_WAIT_ALL,
@ -2566,6 +2572,75 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
goto out_unlock;
}
static int
i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj,
const struct drm_i915_gem_pwrite *arg)
{
struct address_space *mapping = obj->base.filp->f_mapping;
char __user *user_data = u64_to_user_ptr(arg->data_ptr);
u64 remain, offset;
unsigned int pg;
/* Before we instantiate/pin the backing store for our use, we
* can prepopulate the shmemfs filp efficiently using a write into
* the pagecache. We avoid the penalty of instantiating all the
* pages, important if the user is just writing to a few and never
* uses the object on the GPU, and using a direct write into shmemfs
* allows it to avoid the cost of retrieving a page (either swapin
* or clearing-before-use) before it is overwritten.
*/
if (READ_ONCE(obj->mm.pages))
return -ENODEV;
/* Before the pages are instantiated the object is treated as being
* in the CPU domain. The pages will be clflushed as required before
* use, and we can freely write into the pages directly. If userspace
* races pwrite with any other operation; corruption will ensue -
* that is userspace's prerogative!
*/
remain = arg->size;
offset = arg->offset;
pg = offset_in_page(offset);
do {
unsigned int len, unwritten;
struct page *page;
void *data, *vaddr;
int err;
len = PAGE_SIZE - pg;
if (len > remain)
len = remain;
err = pagecache_write_begin(obj->base.filp, mapping,
offset, len, 0,
&page, &data);
if (err < 0)
return err;
vaddr = kmap(page);
unwritten = copy_from_user(vaddr + pg, user_data, len);
kunmap(page);
err = pagecache_write_end(obj->base.filp, mapping,
offset, len, len - unwritten,
page, data);
if (err < 0)
return err;
if (unwritten)
return -EFAULT;
remain -= len;
user_data += len;
offset += len;
pg = 0;
} while (remain);
return 0;
}
static bool ban_context(const struct i915_gem_context *ctx)
{
return (i915_gem_context_is_bannable(ctx) &&
@ -3987,8 +4062,11 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
static const struct drm_i915_gem_object_ops i915_gem_object_ops = {
.flags = I915_GEM_OBJECT_HAS_STRUCT_PAGE |
I915_GEM_OBJECT_IS_SHRINKABLE,
.get_pages = i915_gem_object_get_pages_gtt,
.put_pages = i915_gem_object_put_pages_gtt,
.pwrite = i915_gem_object_pwrite_gtt,
};
struct drm_i915_gem_object *

3
drivers/gpu/drm/i915/i915_gem_object.h
View file

@ -54,6 +54,9 @@ struct drm_i915_gem_object_ops {
struct sg_table *(*get_pages)(struct drm_i915_gem_object *);
void (*put_pages)(struct drm_i915_gem_object *, struct sg_table *);
int (*pwrite)(struct drm_i915_gem_object *,
const struct drm_i915_gem_pwrite *);
int (*dmabuf_export)(struct drm_i915_gem_object *);
void (*release)(struct drm_i915_gem_object *);
};