Re: PROBLEM-PERSISTS: dmesg spam: alloc_contig_range: [XX, YY) PFNs busy

["Robin H. Johnson" <robbat2@gentoo.org>]

(I'm going to respond directly to this email with the stack trace.)

On Wed, Nov 30, 2016 at 02:28:49PM +0100, Michal Hocko wrote:
> > On the other hand, if this didn’t happen and now happens all the time,
> > this indicates a regression in CMA’s capability to allocate pages so
> > just rate limiting the output would hide the potential actual issue.
> 
> Or there might be just a much larger demand on those large blocks, no?
> But seriously, dumping those message again and again into the low (see
> the 2.5_GB_/h to the log is just insane. So there really should be some
> throttling.
> 
> Does the following help you Robin. At least to not get swamped by those
> message.
Here's what I whipped up based on that, to ensure that dump_stack got
rate-limited at the same pass as PFNs-busy. It dropped the dmesg spew to
~25MB/hour (and is suppressing ~43 entries/second right now).

commit 6ad4037e18ec2199f8755274d8a745a9904241a1
Author: Robin H. Johnson <robbat2@gentoo.org>
Date:   Wed Nov 30 10:32:57 2016 -0800

    mm: ratelimit & trace PFNs busy.
    
    Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6de9440e3ae2..3c28ec3d18f8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7289,8 +7289,15 @@ 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",
-			__func__, outer_start, end);
+		static DEFINE_RATELIMIT_STATE(ratelimit_pfn_busy,
+					DEFAULT_RATELIMIT_INTERVAL,
+					DEFAULT_RATELIMIT_BURST);
+		if (__ratelimit(&ratelimit_pfn_busy)) {
+			pr_info("%s: [%lx, %lx) PFNs busy\n",
+				__func__, outer_start, end);
+			dump_stack();
+		}
+
 		ret = -EBUSY;
 		goto done;
 	}

-- 
Robin Hugh Johnson
Gentoo Linux: Dev, Infra Lead, Foundation Trustee & Treasurer
E-Mail   : robbat2@gentoo.org
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