linux-kernel - Re: [PATCH v2 1/5] drm/ttm: add ttm_device_prepare

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Message-ID: <5c4f5f0d-024a-46e5-9506-0b589f6cce5d@amd.com>
Date: Sun, 6 Jul 2025 16:44:27 -0400
From: Mario Limonciello <mario.limonciello@....com>
To: Samuel Zhang <guoqing.zhang@....com>, alexander.deucher@....com,
 christian.koenig@....com, rafael@...nel.org, len.brown@...el.com,
 pavel@...nel.org, gregkh@...uxfoundation.org, dakr@...nel.org,
 airlied@...il.com, simona@...ll.ch, ray.huang@....com,
 matthew.auld@...el.com, matthew.brost@...el.com,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de
Cc: lijo.lazar@....com, victor.zhao@....com, haijun.chang@....com,
 Qing.Ma@....com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 1/5] drm/ttm: add ttm_device_prepare_hibernation() api

On 7/4/2025 6:12 AM, Samuel Zhang wrote:
> This new api is used for hibernation to move GTT BOs to shmem after
> VRAM eviction. shmem will be flushed to swap disk later to reduce
> the system memory usage for hibernation.
> 
> Signed-off-by: Samuel Zhang <guoqing.zhang@....com>
> ---
>   drivers/gpu/drm/ttm/ttm_device.c | 29 +++++++++++++++++++++++++++++
>   include/drm/ttm/ttm_device.h     |  1 +
>   2 files changed, 30 insertions(+)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> index 02e797fd1891..19ab35ffeead 100644
> --- a/drivers/gpu/drm/ttm/ttm_device.c
> +++ b/drivers/gpu/drm/ttm/ttm_device.c
> @@ -123,6 +123,35 @@ static int ttm_global_init(void)
>   	return ret;
>   }
>   
> +/**
> + * move GTT BOs to shmem for hibernation.
> + *
> + * returns 0 on success, negative on failure.
> + */
> +int ttm_device_prepare_hibernation(void)
> +{
> +	struct ttm_operation_ctx ctx = {
> +		.interruptible = false,
> +		.no_wait_gpu = false,
> +		.force_alloc = true
> +	};
> +	struct ttm_global *glob = &ttm_glob;
> +	struct ttm_device *bdev;
> +	int ret = 0;
> +
> +	mutex_lock(&ttm_global_mutex);
> +	list_for_each_entry(bdev, &glob->device_list, device_list) {
> +		do {
> +			ret = ttm_device_swapout(bdev, &ctx, GFP_KERNEL);
> +		} while (ret > 0);
> +		if (ret < 0)
> +			break;
> +	}
> +	mutex_unlock(&ttm_global_mutex);
> +	return ret;

I'd personally rather see scoped guard here so you can return 
immediately and the guard will clean up but up to Christian what he thinks.

int ret;

scoped_guard(mutex, &ttm_global_mutex) {
	list_for_each_entry(bdev, &glob->device_list, device_list) {
		do {
			ret = ttm_device_swapout(bdev, &ctx, GFP_KERNEL);
		} while (ret > 0);
		if (ret)
			return ret;
}

return 0;

> +}
> +EXPORT_SYMBOL(ttm_device_prepare_hibernation);
> +
>   /*
>    * A buffer object shrink method that tries to swap out the first
>    * buffer object on the global::swap_lru list.
> diff --git a/include/drm/ttm/ttm_device.h b/include/drm/ttm/ttm_device.h
> index 39b8636b1845..b45498b398dd 100644
> --- a/include/drm/ttm/ttm_device.h
> +++ b/include/drm/ttm/ttm_device.h
> @@ -272,6 +272,7 @@ struct ttm_device {
>   int ttm_global_swapout(struct ttm_operation_ctx *ctx, gfp_t gfp_flags);
>   int ttm_device_swapout(struct ttm_device *bdev, struct ttm_operation_ctx *ctx,
>   		       gfp_t gfp_flags);
> +int ttm_device_prepare_hibernation(void);
>   
>   static inline struct ttm_resource_manager *
>   ttm_manager_type(struct ttm_device *bdev, int mem_type)