Re: [PATCH] drm/xe: Avoid evicting object of the same vm in none fault mode

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Mon, Dec 02, 2024 at 09:19:29PM -0500, Oak Zeng wrote:
> BO validation during vm_bind could trigger memory eviction when
> system runs under memory pressure. Right now we blindly evict
> BOs of all VMs. This scheme has a problem when system runs in
> none recoverable page fault mode: even though the vm_bind could
> be successful by evicting BOs, the later the rebinding of the
> evicted BOs would fail. So it is better to report an out-of-
> memory failure at vm_bind time than at time of rebinding where
> xekmd currently doesn't have a good mechanism to report error
> to user space.
> 
> This patch implemented a scheme to only evict objects of other
> VMs during vm_bind time. Object of the same VM will skip eviction.
> If we failed to find enough memory for vm_bind, we report error
> to user space at vm_bind time.
> 
> This scheme is not needed for recoverable page fault mode under
> what we can dynamically fault-in pages on demand.
> 
> v1: Use xe_vm_in_preempt_fence_mode instead of stack variable (Thomas)
> 
> Signed-off-by: Oak Zeng <oak.zeng@intel.com>
> Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  drivers/gpu/drm/xe/xe_vm.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 2492750505d69..016fedae5d554 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -2359,13 +2359,15 @@ static int vma_lock_and_validate(struct drm_exec *exec, struct xe_vma *vma,
>  				 bool validate)
>  {
>  	struct xe_bo *bo = xe_vma_bo(vma);
> +	struct xe_vm *vm = xe_vma_vm(vma);

for single usage like below we should avoid variable declaration, specially in
this case where you do have line space left there... then it gets even clear
that the only change in the patch is

- true
+ !xe_vm_in_preempt_fence_mode(vm)

>  	int err = 0;
>  
>  	if (bo) {
>  		if (!bo->vm)
>  			err = drm_exec_lock_obj(exec, &bo->ttm.base);
>  		if (!err && validate)
> -			err = xe_bo_validate(bo, xe_vma_vm(vma), true);
> +			err = xe_bo_validate(bo, vm,
> +					     !xe_vm_in_preempt_fence_mode(vm));
>  	}
>  
>  	return err;
> -- 
> 2.26.3
>