linux-kernel - Re: [PATCH] gpu/drm/ttm: Use mutex_lock

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Message-ID: <alpine.DEB.2.00.1405200140010.20503@skynet.skynet.ie>
Date:	Tue, 20 May 2014 01:40:21 +0100 (IST)
From:	Dave Airlie <airlied@...ux.ie>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
cc:	dchinner@...hat.com, glommer@...nvz.org, mgorman@...e.de,
	linux-kernel@...r.kernel.org,
	DRI mailing list <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] gpu/drm/ttm: Use mutex_lock_killable() for shrinker
 functions.


cc'ing dri-devel.

> >From e314a1a1583e585d062dfc30c8aad8bf5380510b Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Mon, 19 May 2014 18:43:21 +0900
> Subject: [PATCH] gpu/drm/ttm: Use mutex_lock_killable() for shrinker functions.
> 
> I can observe that RHEL7 environment stalls with 100% CPU usage when a
> certain type of memory pressure is given. While the shrinker functions
> are called by shrink_slab() before the OOM killer is triggered, the stall
> lasts for many minutes.
> 
> I added debug printk() and observed that many threads are blocked for more
> than 10 seconds at ttm_dma_pool_shrink_count()/ttm_dma_pool_shrink_scan()
> functions. Since the kswapd can call these functions later, the current
> thread can return from these functions as soon as chosen by the OOM killer.
> 
> This patch changes "mutex_lock();" to "if (mutex_lock_killable()) return ...;"
> so that any threads can promptly give up. (By the way, as far as I tested,
> changing to "if (!mutex_trylock()) return ...;" likely shortens the duration
> of stall. Maybe we don't need to wait for mutex if someone is already calling
> these functions.)
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> ---
>  drivers/gpu/drm/ttm/ttm_page_alloc_dma.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> index 1b79bf0..f75dab8 100644
> --- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> +++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
> @@ -1012,7 +1012,8 @@ ttm_dma_pool_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
>  	if (list_empty(&_manager->pools))
>  		return SHRINK_STOP;
>  
> -	mutex_lock(&_manager->lock);
> +	if (mutex_lock_killable(&_manager->lock))
> +		return SHRINK_STOP;
>  	pool_offset = pool_offset % _manager->npools;
>  	list_for_each_entry(p, &_manager->pools, pools) {
>  		unsigned nr_free;
> @@ -1043,7 +1044,8 @@ ttm_dma_pool_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
>  	struct device_pools *p;
>  	unsigned long count = 0;
>  
> -	mutex_lock(&_manager->lock);
> +	if (mutex_lock_killable(&_manager->lock))
> +		return 0;
>  	list_for_each_entry(p, &_manager->pools, pools)
>  		count += p->pool->npages_free;
>  	mutex_unlock(&_manager->lock);
> 
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