Re: [PATCH] gpu/drm/ttm: Use mutex_lock_killable() for shrinker functions.

cc'ing dri-devel.

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From e314a1a1583e585d062dfc30c8aad8bf5380510b Mon Sep 17 00:00:00 2001

From: Tetsuo Handa penguin-kernel@I-love.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@I-love.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);