linux-kernel - Re: [PATCH] mm: warn about allocations which stall for too long

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Message-Id: <201609232336.FIH57364.FOVHtMFQLFSJOO@I-love.SAKURA.ne.jp>
Date:   Fri, 23 Sep 2016 23:36:22 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     mhocko@...nel.org, linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org, mgorman@...e.de,
        linux-kernel@...r.kernel.org, mhocko@...e.com
Subject: Re: [PATCH] mm: warn about allocations which stall for too long

Michal Hocko wrote:
> @@ -3659,6 +3661,15 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	else
>  		no_progress_loops++;
>  
> +	/* Make sure we know about allocations which stall for too long */
> +	if (!(gfp_mask & __GFP_NOWARN) && time_after(jiffies, alloc_start + stall_timeout)) {

Should we check !__GFP_NOWARN ? I think __GFP_NOWARN is likely used with
__GFP_NORETRY, and __GFP_NORETRY is already checked by now.

I think printing warning regardless of __GFP_NOWARN is better because
this check is similar to hungtask warning.

> +		pr_warn("%s: page alloction stalls for %ums: order:%u mode:%#x(%pGg)\n",
> +				current->comm, jiffies_to_msecs(jiffies-alloc_start),
> +				order, gfp_mask, &gfp_mask);
> +		stall_timeout += 10 * HZ;
> +		dump_stack();

Can we move this pr_warn() + dump_stack() to a separate function like

static void __warn_memalloc_stall(unsigned int order, gfp_t gfp_mask, unsigned long alloc_start)
{
	pr_warn("%s: page alloction stalls for %ums: order:%u mode:%#x(%pGg)\n",
		current->comm, jiffies_to_msecs(jiffies-alloc_start),
		order, gfp_mask, &gfp_mask);
	dump_stack();
}

in order to allow SystemTap scripts to perform additional actions by name (e.g.

# stap -g -e 'probe kernel.function("__warn_memalloc_stall").return { panic(); }

) rather than by line number, and surround __warn_memalloc_stall() call with
mutex in order to serialize warning messages because it is possible that
multiple allocation requests are stalling?

> +	}
> +
>  	if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags,
>  				 did_some_progress > 0, no_progress_loops))
>  		goto retry;
> -- 
> 2.9.3