Re: [PATCH] mm: throttle show_mem from warn_alloc

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 15 Dec 2016 11:15:10 +0100 Michal Hocko <mhocko@kernel.org> wrote:

> Tetsuo has been stressing OOM killer path with many parallel allocation
> requests when he has noticed that it is not all that hard to swamp
> kernel logs with warn_alloc messages caused by allocation stalls. Even
> though the allocation stall message is triggered only once in 10s there
> might be many different tasks hitting it roughly around the same time.
> 
> A big part of the output is show_mem() which can generate a lot of
> output even on a small machines. There is no reason to show the state of
> memory counter for each allocation stall, especially when multiple of
> them are reported in a short time period. Chances are that not much has
> changed since the last report. This patch simply rate limits show_mem
> called from warn_alloc to only dump something once per second. This
> should be enough to give us a clue why an allocation might be stalling
> while burst of warnings will not swamp log with too much data.
> 
> While we are at it, extract all the show_mem related handling (filters)
> into a separate function warn_alloc_show_mem. This will make the code
> cleaner and as a bonus point we can distinguish which part of warn_alloc
> got throttled due to rate limiting as ___ratelimit dumps the caller.

These guys don't need file-wide scope...

--- a/mm/page_alloc.c~mm-throttle-show_mem-from-warn_alloc-fix
+++ a/mm/page_alloc.c
@@ -3018,15 +3018,10 @@ static inline bool should_suppress_show_
 	return ret;
 }
 
-static DEFINE_RATELIMIT_STATE(nopage_rs,
-		DEFAULT_RATELIMIT_INTERVAL,
-		DEFAULT_RATELIMIT_BURST);
-
-static DEFINE_RATELIMIT_STATE(show_mem_rs, HZ, 1);
-
 static void warn_alloc_show_mem(gfp_t gfp_mask)
 {
 	unsigned int filter = SHOW_MEM_FILTER_NODES;
+	static DEFINE_RATELIMIT_STATE(show_mem_rs, HZ, 1);
 
 	if (should_suppress_show_mem() || !__ratelimit(&show_mem_rs))
 		return;
@@ -3050,6 +3045,8 @@ void warn_alloc(gfp_t gfp_mask, const ch
 {
 	struct va_format vaf;
 	va_list args;
+	static DEFINE_RATELIMIT_STATE(nopage_rs, DEFAULT_RATELIMIT_INTERVAL,
+				      DEFAULT_RATELIMIT_BURST);
 
 	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs) ||
 	    debug_guardpage_minorder() > 0)
_