linux-kernel - Re: [PATCH] mm: throttle show_mem from warn

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Date:   Tue, 20 Dec 2016 09:35:38 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: throttle show_mem from warn_alloc

On Mon 19-12-16 15:21:25, Andrew Morton wrote:
> On Thu, 15 Dec 2016 11:15:10 +0100 Michal Hocko <mhocko@...nel.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)
> _
> 

Acked-by: Michal Hocko <mhocko@...e.com>

-- 
Michal Hocko
SUSE Labs