Re: [PATCH v3 1/4] drm/xe: Add devcoredump chunking

[John Harrison <john.c.harrison@intel.com>]

On 4/9/2025 9:06 PM, Matthew Brost wrote:
> Chunk devcoredump into 1.5G pieces to avoid hitting the kvmalloc limit
> of 2G. Simple algorithm reads 1.5G at time in xe_devcoredump_read
> callback as needed.
>
> Some memory allocations are changed to GFP_ATOMIC as they done in
> xe_devcoredump_read which holds lock in the path of reclaim. The
> allocations are small, so in practice should never fail.
>
> v2:
>   - Update commit message wrt gfp atomic (John H)
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_devcoredump.c       | 59 ++++++++++++++++++-----
>   drivers/gpu/drm/xe/xe_devcoredump_types.h |  2 +
>   drivers/gpu/drm/xe/xe_guc_hwconfig.c      |  2 +-
>   3 files changed, 50 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_devcoredump.c b/drivers/gpu/drm/xe/xe_devcoredump.c
> index 81b9d9bb3f57..a9e618abf8ac 100644
> --- a/drivers/gpu/drm/xe/xe_devcoredump.c
> +++ b/drivers/gpu/drm/xe/xe_devcoredump.c
> @@ -80,7 +80,8 @@ static struct xe_guc *exec_queue_to_guc(struct xe_exec_queue *q)
>   	return &q->gt->uc.guc;
>   }
>   
> -static ssize_t __xe_devcoredump_read(char *buffer, size_t count,
> +static ssize_t __xe_devcoredump_read(char *buffer, ssize_t count,
> +				     ssize_t start,
>   				     struct xe_devcoredump *coredump)
>   {
>   	struct xe_device *xe;
> @@ -94,7 +95,7 @@ static ssize_t __xe_devcoredump_read(char *buffer, size_t count,
>   	ss = &coredump->snapshot;
>   
>   	iter.data = buffer;
> -	iter.start = 0;
> +	iter.start = start;
>   	iter.remain = count;
>   
>   	p = drm_coredump_printer(&iter);
> @@ -168,6 +169,8 @@ static void xe_devcoredump_snapshot_free(struct xe_devcoredump_snapshot *ss)
>   	ss->vm = NULL;
>   }
>   
> +#define XE_DEVCOREDUMP_CHUNK_MAX	(SZ_512M + SZ_1G)
> +
>   static ssize_t xe_devcoredump_read(char *buffer, loff_t offset,
>   				   size_t count, void *data, size_t datalen)
>   {
> @@ -183,6 +186,9 @@ static ssize_t xe_devcoredump_read(char *buffer, loff_t offset,
>   	/* Ensure delayed work is captured before continuing */
>   	flush_work(&ss->work);
>   
> +	if (ss->read.size > XE_DEVCOREDUMP_CHUNK_MAX)
> +		xe_pm_runtime_get(gt_to_xe(ss->gt));
> +
>   	mutex_lock(&coredump->lock);
>   
>   	if (!ss->read.buffer) {
> @@ -195,12 +201,26 @@ static ssize_t xe_devcoredump_read(char *buffer, loff_t offset,
>   		return 0;
>   	}
>   
> +	if (offset >= ss->read.chunk_position + XE_DEVCOREDUMP_CHUNK_MAX ||
> +	    offset < ss->read.chunk_position) {
> +		ss->read.chunk_position =
> +			ALIGN_DOWN(offset, XE_DEVCOREDUMP_CHUNK_MAX);
> +
> +		__xe_devcoredump_read(ss->read.buffer,
> +				      XE_DEVCOREDUMP_CHUNK_MAX,
> +				      ss->read.chunk_position, coredump);
> +	}
> +
>   	byte_copied = count < ss->read.size - offset ? count :
>   		ss->read.size - offset;
> -	memcpy(buffer, ss->read.buffer + offset, byte_copied);
> +	memcpy(buffer, ss->read.buffer +
> +	       (offset % XE_DEVCOREDUMP_CHUNK_MAX), byte_copied);
>   
>   	mutex_unlock(&coredump->lock);
>   
> +	if (ss->read.size > XE_DEVCOREDUMP_CHUNK_MAX)
> +		xe_pm_runtime_put(gt_to_xe(ss->gt));
> +
>   	return byte_copied;
>   }
>   
> @@ -254,17 +274,32 @@ static void xe_devcoredump_deferred_snap_work(struct work_struct *work)
>   	xe_guc_exec_queue_snapshot_capture_delayed(ss->ge);
>   	xe_force_wake_put(gt_to_fw(ss->gt), fw_ref);
>   
> -	xe_pm_runtime_put(xe);
> +	ss->read.chunk_position = 0;
>   
>   	/* Calculate devcoredump size */
> -	ss->read.size = __xe_devcoredump_read(NULL, INT_MAX, coredump);
> -
> -	ss->read.buffer = kvmalloc(ss->read.size, GFP_USER);
> -	if (!ss->read.buffer)
> -		return;
> +	ss->read.size = __xe_devcoredump_read(NULL, LONG_MAX, 0, coredump);
> +
> +	if (ss->read.size > XE_DEVCOREDUMP_CHUNK_MAX) {
> +		ss->read.buffer = kvmalloc(XE_DEVCOREDUMP_CHUNK_MAX,
> +					   GFP_USER);
> +		if (!ss->read.buffer)
> +			goto put_pm;
> +
> +		__xe_devcoredump_read(ss->read.buffer,
> +				      XE_DEVCOREDUMP_CHUNK_MAX,
> +				      0, coredump);
> +	} else {
> +		ss->read.buffer = kvmalloc(ss->read.size, GFP_USER);
> +		if (!ss->read.buffer)
> +			goto put_pm;
> +
> +		__xe_devcoredump_read(ss->read.buffer, ss->read.size, 0,
> +				      coredump);
> +		xe_devcoredump_snapshot_free(ss);
> +	}
>   
> -	__xe_devcoredump_read(ss->read.buffer, ss->read.size, coredump);
> -	xe_devcoredump_snapshot_free(ss);
> +put_pm:
> +	xe_pm_runtime_put(xe);
>   }
>   
>   static void devcoredump_snapshot(struct xe_devcoredump *coredump,
> @@ -425,7 +460,7 @@ void xe_print_blob_ascii85(struct drm_printer *p, const char *prefix, char suffi
>   	if (offset & 3)
>   		drm_printf(p, "Offset not word aligned: %zu", offset);
>   
> -	line_buff = kzalloc(DMESG_MAX_LINE_LEN, GFP_KERNEL);
> +	line_buff = kzalloc(DMESG_MAX_LINE_LEN, GFP_ATOMIC);
>   	if (!line_buff) {
>   		drm_printf(p, "Failed to allocate line buffer\n");
>   		return;
> diff --git a/drivers/gpu/drm/xe/xe_devcoredump_types.h b/drivers/gpu/drm/xe/xe_devcoredump_types.h
> index 1a1d16a96b2d..a174385a6d83 100644
> --- a/drivers/gpu/drm/xe/xe_devcoredump_types.h
> +++ b/drivers/gpu/drm/xe/xe_devcoredump_types.h
> @@ -66,6 +66,8 @@ struct xe_devcoredump_snapshot {
>   	struct {
>   		/** @read.size: size of devcoredump in human readable format */
>   		ssize_t size;
> +		/** @read.chunk_position: position of devcoredump chunk */
> +		ssize_t chunk_position;
>   		/** @read.buffer: buffer of devcoredump in human readable format */
>   		char *buffer;
>   	} read;
> diff --git a/drivers/gpu/drm/xe/xe_guc_hwconfig.c b/drivers/gpu/drm/xe/xe_guc_hwconfig.c
> index af2c817d552c..21403a250834 100644
> --- a/drivers/gpu/drm/xe/xe_guc_hwconfig.c
> +++ b/drivers/gpu/drm/xe/xe_guc_hwconfig.c
> @@ -175,7 +175,7 @@ int xe_guc_hwconfig_lookup_u32(struct xe_guc *guc, u32 attribute, u32 *val)
>   	if (num_dw == 0)
>   		return -EINVAL;
>   
> -	hwconfig = kzalloc(size, GFP_KERNEL);
> +	hwconfig = kzalloc(size, GFP_ATOMIC);
Did you work out what was going on here? It seems like this really 
should not be happening.

John.

>   	if (!hwconfig)
>   		return -ENOMEM;
>