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

From: Doug Ledford
Date: Wed Aug 02 2017 - 14:05:27 EST


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@xxxxxxxxxx>
> Reviewed-by: Doug Ledford <dledford@xxxxxxxxxx>
> Tested-by: Doug Ledford <dledford@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxx>
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