Re: [PATCH v2 1/2] ring-buffer: Skip si_mem_available() for persistent and remote buffers

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 13 Oct 2026 11:20:46 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:

> Persistent and remote buffer memory is pre-allocated by the time
> __rb_allocate_pages() is called. Skip si_mem_available() to avoid
> wrongly failing the allocation under memory pressure.
> 
> For the same reason, unset user_thread.
> 
> Fixes: be68d63a139b ("ring-buffer: Add ring_buffer_alloc_range()")
> Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes")
> Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
> ---
>  kernel/trace/ring_buffer.c | 41 +++++++++++++++++++-------------------
>  1 file changed, 21 insertions(+), 20 deletions(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 04bb94c29f58..b3a30a0413a5 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -2442,20 +2442,30 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
>  	struct trace_buffer *buffer = cpu_buffer->buffer;
>  	struct ring_buffer_cpu_meta *meta = NULL;
>  	struct buffer_page *bpage, *tmp;
> -	bool user_thread = current->mm != NULL;
>  	struct ring_buffer_desc *desc = NULL;
> +	bool user_thread = false;
>  	long i;
>  
> -	/*
> -	 * Check if the available memory is there first.
> -	 * Note, si_mem_available() only gives us a rough estimate of available
> -	 * memory. It may not be accurate. But we don't care, we just want
> -	 * to prevent doing any allocation when it is obvious that it is
> -	 * not going to succeed.
> -	 */
> -	i = si_mem_available();
> -	if (i < nr_pages)
> -		return -ENOMEM;
> +	if (buffer->range_addr_start) {
> +		meta = rb_range_meta(buffer, nr_pages, cpu_buffer->cpu);
> +	} else if (buffer->remote) {
> +		desc = ring_buffer_desc(buffer->remote->desc, cpu_buffer->cpu);
> +		if (!desc || WARN_ON(desc->nr_page_va != (nr_pages + 1)))
> +			return -EINVAL;
> +	} else {
> +		/*
> +		 * Check if the available memory is there first.
> +		 * Note, si_mem_available() only gives us a rough estimate of available
> +		 * memory. It may not be accurate. But we don't care, we just want
> +		 * to prevent doing any allocation when it is obvious that it is
> +		 * not going to succeed.
> +		 */
> +		i = si_mem_available();
> +		if (i < nr_pages)
> +			return -ENOMEM;
> +
> +		user_thread = current->mm != NULL;

Not caused by this patch but we need to update this to:

		user_thread = is_user_task(current);

I may add that.

-- Steve

> +	}
>  
>  	/*
>  	 * If a user thread allocates too much, and si_mem_available()
> @@ -2469,15 +2479,6 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
>  	if (user_thread)
>  		set_current_oom_origin();
>  
> -	if (buffer->range_addr_start)
> -		meta = rb_range_meta(buffer, nr_pages, cpu_buffer->cpu);
> -
> -	if (buffer->remote) {
> -		desc = ring_buffer_desc(buffer->remote->desc, cpu_buffer->cpu);
> -		if (!desc || WARN_ON(desc->nr_page_va != (nr_pages + 1)))
> -			return -EINVAL;
> -	}
> -
>  	for (i = 0; i < nr_pages; i++) {
>  
>  		bpage = alloc_cpu_page(cpu_buffer->cpu);