Re: [PATCH 2/5] drm/gem: add shmem get/put page helpers

[Rob Clark <robdclark@gmail.com>]

On Mon, Jul 8, 2013 at 4:18 PM, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Mon, Jul 08, 2013 at 02:56:31PM -0400, Rob Clark wrote:
>> On Mon, Jul 8, 2013 at 4:45 AM, Patrik Jakobsson
>> <patrik.r.jakobsson@gmail.com> wrote:
>> > On Sun, Jul 7, 2013 at 8:58 PM, Rob Clark <robdclark@gmail.com> wrote:
>> >> Basically just extracting some code duplicated in gma500, omapdrm, udl,
>> >> and upcoming msm driver.
>> >>
>> >> Signed-off-by: Rob Clark <robdclark@gmail.com>
>> >> ---
>> >>  drivers/gpu/drm/drm_gem.c | 91 +++++++++++++++++++++++++++++++++++++++++++++++
>> >>  include/drm/drmP.h        |  4 +++
>> >>  2 files changed, 95 insertions(+)
>> >>
>> >> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>> >> index 443eeff..853dea6 100644
>> >> --- a/drivers/gpu/drm/drm_gem.c
>> >> +++ b/drivers/gpu/drm/drm_gem.c
>> >> @@ -406,6 +406,97 @@ int drm_gem_create_mmap_offset(struct drm_gem_object *obj)
>> >>  }
>> >>  EXPORT_SYMBOL(drm_gem_create_mmap_offset);
>> >>
>> >> +/**
>> >> + * drm_gem_get_pages - helper to allocate backing pages for a GEM object
>> >> + * from shmem
>> >> + * @obj: obj in question
>> >> + * @gfpmask: gfp mask of requested pages
>> >> + */
>> >> +struct page **drm_gem_get_pages(struct drm_gem_object *obj, gfp_t gfpmask)
>> >> +{
>> >> +       struct inode *inode;
>> >> +       struct address_space *mapping;
>> >> +       struct page *p, **pages;
>> >> +       int i, npages;
>> >> +
>> >> +       /* This is the shared memory object that backs the GEM resource */
>> >> +       inode = file_inode(obj->filp);
>> >> +       mapping = inode->i_mapping;
>> >> +
>> >> +       npages = obj->size >> PAGE_SHIFT;
>> >
>> > Theoretical issue, but what if obj->size is not page aligned? Perhaps put a
>> > roundup(obj->size, PAGE_SIZE) here?
>>
>> so, drm_gem_object_init() does have:
>>
>>       BUG_ON((size & (PAGE_SIZE - 1)) != 0);
>>
>> so I was kinda assuming that we can count on the size already being
>> aligned.  But I guess in case someone somehow bypasses
>> drm_gem_object_init() it wouldn't hurt to round up the size..
>
> Would look funny to me to allow it in one place and not in another one.
> Maybe just throw a new WARN_ON in here (WARN since it's not fatal)?
> -Daniel

sounds good, I'll toss in a WARN_ON()

BR,
-R


>>
>> BR,
>> -R
>>
>> >> +
>> >> +       pages = drm_malloc_ab(npages, sizeof(struct page *));
>> >> +       if (pages == NULL)
>> >> +               return ERR_PTR(-ENOMEM);
>> >> +
>> >> +       gfpmask |= mapping_gfp_mask(mapping);
>> >> +
>> >> +       for (i = 0; i < npages; i++) {
>> >> +               p = shmem_read_mapping_page_gfp(mapping, i, gfpmask);
>> >> +               if (IS_ERR(p))
>> >> +                       goto fail;
>> >> +               pages[i] = p;
>> >> +
>> >> +               /* There is a hypothetical issue w/ drivers that require
>> >> +                * buffer memory in the low 4GB.. if the pages are un-
>> >> +                * pinned, and swapped out, they can end up swapped back
>> >> +                * in above 4GB.  If pages are already in memory, then
>> >> +                * shmem_read_mapping_page_gfp will ignore the gfpmask,
>> >> +                * even if the already in-memory page disobeys the mask.
>> >> +                *
>> >> +                * It is only a theoretical issue today, because none of
>> >> +                * the devices with this limitation can be populated with
>> >> +                * enough memory to trigger the issue.  But this BUG_ON()
>> >> +                * is here as a reminder in case the problem with
>> >> +                * shmem_read_mapping_page_gfp() isn't solved by the time
>> >> +                * it does become a real issue.
>> >> +                *
>> >> +                * See this thread: http://lkml.org/lkml/2011/7/11/238
>> >> +                */
>> >> +               BUG_ON((gfpmask & __GFP_DMA32) &&
>> >> +                               (page_to_pfn(p) >= 0x00100000UL));
>> >> +       }
>> >> +
>> >> +       return pages;
>> >> +
>> >> +fail:
>> >> +       while (i--)
>> >> +               page_cache_release(pages[i]);
>> >> +
>> >> +       drm_free_large(pages);
>> >> +       return ERR_CAST(p);
>> >> +}
>> >> +EXPORT_SYMBOL(drm_gem_get_pages);
>> >> +
>> >> +/**
>> >> + * drm_gem_put_pages - helper to free backing pages for a GEM object
>> >> + * @obj: obj in question
>> >> + * @pages: pages to free
>> >> + * @dirty: if true, pages will be marked as dirty
>> >> + * @accessed: if true, the pages will be marked as accessed
>> >> + */
>> >> +void drm_gem_put_pages(struct drm_gem_object *obj, struct page **pages,
>> >> +               bool dirty, bool accessed)
>> >> +{
>> >> +       int i, npages;
>> >> +
>> >> +       npages = obj->size >> PAGE_SHIFT;
>> >
>> > Same thing here.
>> >
>> >> +
>> >> +       for (i = 0; i < npages; i++) {
>> >> +               if (dirty)
>> >> +                       set_page_dirty(pages[i]);
>> >> +
>> >> +               if (accessed)
>> >> +                       mark_page_accessed(pages[i]);
>> >> +
>> >> +               /* Undo the reference we took when populating the table */
>> >> +               page_cache_release(pages[i]);
>> >> +       }
>> >> +
>> >> +       drm_free_large(pages);
>> >> +}
>> >> +EXPORT_SYMBOL(drm_gem_put_pages);
>> >> +
>> >>  /** Returns a reference to the object named by the handle. */
>> >>  struct drm_gem_object *
>> >>  drm_gem_object_lookup(struct drm_device *dev, struct drm_file *filp,
>> >> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
>> >> index 3cb1672..7ec3fa4 100644
>> >> --- a/include/drm/drmP.h
>> >> +++ b/include/drm/drmP.h
>> >> @@ -1730,6 +1730,10 @@ void drm_gem_free_mmap_offset(struct drm_gem_object *obj);
>> >>  int drm_gem_create_mmap_offset(struct drm_gem_object *obj);
>> >>  int drm_gem_create_mmap_offset_size(struct drm_gem_object *obj, size_t size);
>> >>
>> >> +struct page **drm_gem_get_pages(struct drm_gem_object *obj, gfp_t gfpmask);
>> >> +void drm_gem_put_pages(struct drm_gem_object *obj, struct page **pages,
>> >> +               bool dirty, bool accessed);
>> >> +
>> >>  struct drm_gem_object *drm_gem_object_lookup(struct drm_device *dev,
>> >>                                              struct drm_file *filp,
>> >>                                              u32 handle);
>> >> --
>> >> 1.8.1.4
>> >
>> > Looks good otherwise, so for all 5 patches:
>> > Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
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>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch