Re: [PATCH] mm: ratelimit PFNs busy info message

[Doug Ledford <dledford@redhat.com>]

On Wed, 2017-08-02 at 13:44 -0400, Jonathan Toppins wrote:
> The RDMA subsystem can generate several thousand of these messages
> per
> second eventually leading to a kernel crash. Ratelimit these messages
> to prevent this crash.
> 
> Signed-off-by: Jonathan Toppins <jtoppins@redhat.com>
> Reviewed-by: Doug Ledford <dledford@redhat.com>
> Tested-by: Doug Ledford <dledford@redhat.com>
> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6d30e914afb6..07b7d3060b21 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7666,7 +7666,7 @@ int alloc_contig_range(unsigned long start,
> unsigned long end,
>  
>  	/* Make sure the range is really isolated. */
>  	if (test_pages_isolated(outer_start, end, false)) {
> -		pr_info("%s: [%lx, %lx) PFNs busy\n",
> +		pr_info_ratelimited("%s: [%lx, %lx) PFNs busy\n",
>  			__func__, outer_start, end);
>  		ret = -EBUSY;
>  		goto done;


FWIW, I've been carrying a version of this for several kernel versions.
 I don't remember when they started, but we have one (and only one)
class of machines: Dell PE R730xd, that generate these errors.  When it
happens, without a rate limit, we get rcu timeouts and kernel oopses. 
With the rate limit, we just get a lot of annoying kernel messages but
the machine continues on, recovers, and eventually the memory
operations all succeed.

-- 
Doug Ledford <dledford@redhat.com>
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