[PATCH] drm/vc4: Add the DRM_IOCTL_VC4_GEM_MADVISE ioctl

[Eric Anholt]

Boris Brezillon <boris.brezillon at free-electrons.com> writes:

> This ioctl will allow us to purge inactive userspace buffers when the
> system is running out of contiguous memory.
>
> For now, the purge logic is rather dumb in that it does not try to
> release only the amount of BO needed to meet the last CMA alloc request
> but instead purges all objects placed in the purgeable pool as soon as
> we experience a CMA allocation failure.
>
> Note that the in-kernel BO cache is always purged before the purgeable
> cache because those objects are known to be unused while objects marked
> as purgeable by a userspace application/library might have to be
> restored when they are marked back as unpurgeable, which can be
> expensive.
>
> Signed-off-by: Boris Brezillon <boris.brezillon at free-electrons.com>
> ---
> Hello,
>
> Updates to libdrm, mesa and igt making use of this kernel feature can
> be found on my github repos [1][2][3].
>
> There's currently no debugfs hook to manually force a purge, but this
> is being discussed and will probably be added in v2.
>
> Regards,

> diff --git a/include/uapi/drm/vc4_drm.h b/include/uapi/drm/vc4_drm.h
> index afae87004963..c01b93d453db 100644
> --- a/include/uapi/drm/vc4_drm.h
> +++ b/include/uapi/drm/vc4_drm.h
> @@ -41,6 +41,7 @@ extern "C" {
>  #define DRM_VC4_SET_TILING                        0x08
>  #define DRM_VC4_GET_TILING                        0x09
>  #define DRM_VC4_LABEL_BO                          0x0a
> +#define DRM_VC4_GEM_MADVISE                       0x0b
>  
>  #define DRM_IOCTL_VC4_SUBMIT_CL           DRM_IOWR(DRM_COMMAND_BASE + DRM_VC4_SUBMIT_CL, struct drm_vc4_submit_cl)
>  #define DRM_IOCTL_VC4_WAIT_SEQNO          DRM_IOWR(DRM_COMMAND_BASE + DRM_VC4_WAIT_SEQNO, struct drm_vc4_wait_seqno)
> @@ -53,6 +54,7 @@ extern "C" {
>  #define DRM_IOCTL_VC4_SET_TILING          DRM_IOWR(DRM_COMMAND_BASE + DRM_VC4_SET_TILING, struct drm_vc4_set_tiling)
>  #define DRM_IOCTL_VC4_GET_TILING          DRM_IOWR(DRM_COMMAND_BASE + DRM_VC4_GET_TILING, struct drm_vc4_get_tiling)
>  #define DRM_IOCTL_VC4_LABEL_BO            DRM_IOWR(DRM_COMMAND_BASE + DRM_VC4_LABEL_BO, struct drm_vc4_label_bo)
> +#define DRM_IOCTL_VC4_GEM_MADVISE         DRM_IOWR(DRM_COMMAND_BASE + DRM_VC4_GEM_MADVISE, struct drm_vc4_gem_madvise)
>  
>  struct drm_vc4_submit_rcl_surface {
>  	__u32 hindex; /* Handle index, or ~0 if not present. */
> @@ -333,6 +335,16 @@ struct drm_vc4_label_bo {
>  	__u64 name;
>  };
>  
> +#define VC4_MADV_WILLNEED			0
> +#define VC4_MADV_DONTNEED			1
> +#define __VC4_MADV_PURGED			2
> +
> +struct drm_vc4_gem_madvise {
> +	__u32 handle;
> +	__u32 madv;
> +	__u32 retained;
> +};

danvet had a note in
http://blog.ffwll.ch/2013/11/botching-up-ioctls.html:

    Pad the entire struct to a multiple of 64bits - the structure size
    will otherwise differ on 32bit versus 64bit. Which hurts when
    passing arrays of structures to the kernel. Or with the ioctl
    structure size checking that e.g. the drm core does.

I'm surprised that i915's ioctl didn't do this or have compat code to
handle it.
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