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

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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@xxxxxxxxx> wrote:
> > On Sun, Jul 7, 2013 at 8:58 PM, Rob Clark <robdclark@xxxxxxxxx> wrote:
> >> Basically just extracting some code duplicated in gma500, omapdrm, udl,
> >> and upcoming msm driver.
> >>
> >> Signed-off-by: Rob Clark <robdclark@xxxxxxxxx>
> >> ---
> >>  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

> 
> 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@xxxxxxxxx>
> _______________________________________________
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> http://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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