[PATCH v2 0/2] ring-buffer: Fixes for available memory estimation

[PATCH v2 0/2] ring-buffer: Fixes for available memory estimation

[Vincent Donnefort]

__rb_allocate_pages() uses si_mem_available() to fail early when there
is not enough memory for a ring buffer allocation. However it wasn't
updated with the introduction of persistent and remote buffers and
subbuf_order.

v2:
  - Add "ring-buffer: Use subbuf_order in available memory estimation"

v1: https://lore.kernel.org/all/20261012163502.687061-1-vdonnefort@google.com/

Vincent Donnefort (2):
  ring-buffer: Skip si_mem_available() for persistent and remote buffers
  ring-buffer: Use subbuf_order in available memory estimation

 kernel/trace/ring_buffer.c | 47 +++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 23 deletions(-)


base-commit: 24a19b953e2a3d0ea5a8c4951a0ab8f32720c907
-- 
2.56.0.385.gd3acb90ef8-goog

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

[Vincent Donnefort]

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;
+	}
 
 	/*
 	 * 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);
-- 
2.56.0.385.gd3acb90ef8-goog

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

[Steven Rostedt]

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);

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

[Vincent Donnefort]

On Wed, Oct 14, 2026 at 05:51:26PM -0400, Steven Rostedt wrote:
> 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.

I can send a v3 if that helps.

-- 
Vincent

> 
> -- 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);
> 

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

[Steven Rostedt]

On Thu, 15 Oct 2026 09:39:31 +0100
Vincent Donnefort <vdonnefort@google.com> wrote:


> > Not caused by this patch but we need to update this to:
> > 
> > 		user_thread = is_user_task(current);
> > 
> > I may add that.  
> 
> I can send a v3 if that helps.
> 

I already pulled in the other two patches and tested them.

This can be a clean up for the merge window.

-- Steve

[PATCH v2 2/2] ring-buffer: Use subbuf_order in available memory estimation

[Vincent Donnefort]

To avoid failing in the middle of an allocation of a ring-buffer,
__rb_allocate_pages() looks at the available memory estimation with
si_mem_available(). Use the subbuffer order with this estimation to fail
early if necessary for ring-buffers with an order > 0.

Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page")
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
---
 kernel/trace/ring_buffer.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index b3a30a0413a5..63001ab1eef2 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2440,6 +2440,7 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 			       unsigned long nr_pages, struct list_head *pages)
 {
 	struct trace_buffer *buffer = cpu_buffer->buffer;
+	unsigned int subbuf_order = buffer->subbuf_order;
 	struct ring_buffer_cpu_meta *meta = NULL;
 	struct buffer_page *bpage, *tmp;
 	struct ring_buffer_desc *desc = NULL;
@@ -2461,7 +2462,7 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 		 * not going to succeed.
 		 */
 		i = si_mem_available();
-		if (i < nr_pages)
+		if (i < (nr_pages << subbuf_order))
 			return -ENOMEM;
 
 		user_thread = current->mm != NULL;
@@ -2514,12 +2515,11 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 			bpage->id = i + 1;
 			cpu_buffer->subbuf_ids[i + 1] = bpage;
 		} else {
-			bpage->page = alloc_cpu_data(cpu_buffer->cpu,
-						     cpu_buffer->buffer->subbuf_order);
+			bpage->page = alloc_cpu_data(cpu_buffer->cpu, subbuf_order);
 			if (!bpage->page)
 				goto free_pages;
 		}
-		bpage->order = cpu_buffer->buffer->subbuf_order;
+		bpage->order = subbuf_order;
 
 		if (user_thread && fatal_signal_pending(current))
 			goto free_pages;
-- 
2.56.0.385.gd3acb90ef8-goog

Re: [PATCH v2 2/2] ring-buffer: Use subbuf_order in available memory estimation

[Masami Hiramatsu]

On Tue, 13 Oct 2026 11:20:47 +0100, Vincent Donnefort <vdonnefort@google.com> wrote:
> To avoid failing in the middle of an allocation of a ring-buffer,
> __rb_allocate_pages() looks at the available memory estimation with
> si_mem_available(). Use the subbuffer order with this estimation to fail
> early if necessary for ring-buffers with an order > 0.
>
> Fixes: f9b94daa542a ("ring-buffer: Set new size of the ring buffer sub page")
> Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

Looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks,

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>