linux-kernel - Re: [PATCH] trace: Set __GFP_NORETRY flag for ring buffer allocating process

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Date:	Wed, 8 Jun 2011 01:47:15 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Michael Rubin <mrubin@...gle.com>,
	David Sharp <dhsharp@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] trace: Set __GFP_NORETRY flag for ring buffer allocating
 process

On Tue, Jun 07, 2011 at 04:41:28PM -0700, Vaibhav Nagarnaik wrote:
> The tracing ring buffer is allocated from kernel memory. While
> allocating a large chunk of memory, OOM might happen which destabilizes
> the system. Thus random processes might get killed during the
> allocation.
> 
> This patch adds __GFP_NORETRY flag to the ring buffer allocation calls
> to make it fail more gracefully if the system will not be able to
> complete the allocation request.
> 
> Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@...gle.com>
> ---
>  kernel/trace/ring_buffer.c |   15 ++++++++++-----
>  1 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 2780e60..ec817d5 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1005,7 +1005,8 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
>  	for (i = 0; i < nr_pages; i++) {
>  		struct page *page;
>  		bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
> -				    GFP_KERNEL, cpu_to_node(cpu_buffer->cpu));
> +				    GFP_KERNEL | __GFP_NORETRY,

Please put a comment in the code to explain the reason of this __GFP_NORETRY.
It's pretty hard without the changelog.

Thanks.
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