linux-kernel - [PATCH] mm: rate-limit allocation failure warnings more aggressively

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Message-Id: <20191028194906.26899-1-hannes@cmpxchg.org>
Date:   Mon, 28 Oct 2019 15:49:06 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: [PATCH] mm: rate-limit allocation failure warnings more aggressively

While investigating a bug related to higher atomic allocation
failures, we noticed the failure warnings positively drowning the
console, and in our case trigger lockup warnings because of a serial
console too slow to handle all that output.

But even if we had a faster console, it's unclear what additional
information the current level of repetition provides.

Allocation failures happen for three reasons: The machine is OOM, the
VM is failing to handle reasonable requests, or somebody is making
unreasonable requests (and didn't acknowledge their opportunism with
__GFP_NOWARN). Having the memory dump, a callstack, and the ratelimit
stats on skipped failure warnings should provide enough information to
let users/admins/developers know whether something is wrong and point
them in the right direction for debugging, bpftracing etc.

Limit allocation failure warnings to 1 spew every ten seconds.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/page_alloc.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 791c018314b3..f412b17b5d59 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3720,10 +3720,6 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
 {
 	unsigned int filter = SHOW_MEM_FILTER_NODES;
-	static DEFINE_RATELIMIT_STATE(show_mem_rs, HZ, 1);
-
-	if (!__ratelimit(&show_mem_rs))
-		return;

 	/*
 	 * This documents exceptions given to allocations in certain
@@ -3744,8 +3740,7 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
-	static DEFINE_RATELIMIT_STATE(nopage_rs, DEFAULT_RATELIMIT_INTERVAL,
-				      DEFAULT_RATELIMIT_BURST);
+	static DEFINE_RATELIMIT_STATE(nopage_rs, 10*HZ, 1);

 	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs))
 		return;
-- 
2.23.0