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From: Vladimir Davydov <vdavydov.dev@gmail.com>
To: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: akpm@linux-foundation.org, shakeelb@google.com,
	viro@zeniv.linux.org.uk, hannes@cmpxchg.org, mhocko@kernel.org,
	tglx@linutronix.de, pombredanne@nexb.com,
	stummala@codeaurora.org, gregkh@linuxfoundation.org,
	sfr@canb.auug.org.au, guro@fb.com, mka@chromium.org,
	penguin-kernel@I-love.SAKURA.ne.jp, chris@chris-wilson.co.uk,
	longman@redhat.com, minchan@kernel.org, ying.huang@intel.com,
	mgorman@techsingularity.net, jbacik@fb.com, linux@roeck-us.net,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	willy@infradead.org, lirongqing@baidu.com,
	aryabinin@virtuozzo.com
Subject: Re: [PATCH v5 13/13] mm: Clear shrinker bit if there are no objects related to memcg
Date: Thu, 17 May 2018 07:49:24 +0300	[thread overview]
Message-ID: <20180517044924.5tq6vbqituvr3nzh@esperanza> (raw)
In-Reply-To: <1e31235c-f4e3-1046-57c8-741de095e616@virtuozzo.com>

On Tue, May 15, 2018 at 11:55:04AM +0300, Kirill Tkhai wrote:
> >> @@ -586,8 +586,23 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
> >>  			continue;
> >>  
> >>  		ret = do_shrink_slab(&sc, shrinker, priority);
> >> -		if (ret == SHRINK_EMPTY)
> >> -			ret = 0;
> >> +		if (ret == SHRINK_EMPTY) {
> >> +			clear_bit(i, map->map);
> >> +			/*
> >> +			 * Pairs with mb in memcg_set_shrinker_bit():
> >> +			 *
> >> +			 * list_lru_add()     shrink_slab_memcg()
> >> +			 *   list_add_tail()    clear_bit()
> >> +			 *   <MB>               <MB>
> >> +			 *   set_bit()          do_shrink_slab()
> >> +			 */
> > 
> > Please improve the comment so that it isn't just a diagram.
> 
> Please, say, which comment you want to see here.

I want the reader to understand why we need to invoke the shrinker twice
if it returns SHRINK_EMPTY. The diagram doesn't really help here IMO. So
I'd write Something like this:

	ret = do_shrink_slab(&sc, shrinker, priority);
	if (ret == SHRINK_EMPTY) {
		clear_bit(i, map->map);
		/*
		 * After the shrinker reported that it had no objects to free,
		 * but before we cleared the corresponding bit in the memcg
		 * shrinker map, a new object might have been added. To make
		 * sure, we have the bit set in this case, we invoke the
		 * shrinker one more time and re-set the bit if it reports that
		 * it is not empty anymore. The memory barrier here pairs with
		 * the barrier in memcg_set_shrinker_bit():
		 *
		 * list_lru_add()     shrink_slab_memcg()
		 *   list_add_tail()    clear_bit()
		 *   <MB>               <MB>
		 *   set_bit()          do_shrink_slab()
		 */
		smp_mb__after_atomic();
		ret = do_shrink_slab(&sc, shrinker, priority);
			if (ret == SHRINK_EMPTY)
				ret = 0;
			else
				memcg_set_shrinker_bit(memcg, nid, i);

      reply	other threads:[~2018-05-17  4:49 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-10  9:52 [PATCH v5 00/13] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n)) Kirill Tkhai
2018-05-10  9:52 ` [PATCH v5 01/13] mm: Assign id to every memcg-aware shrinker Kirill Tkhai
2018-05-13  5:15   ` Vladimir Davydov
2018-05-14  9:03     ` Kirill Tkhai
2018-05-15  3:29       ` Vladimir Davydov
2018-05-10  9:52 ` [PATCH v5 02/13] memcg: Move up for_each_mem_cgroup{, _tree} defines Kirill Tkhai
2018-05-10  9:52 ` [PATCH v5 03/13] mm: Assign memcg-aware shrinkers bitmap to memcg Kirill Tkhai
2018-05-13 16:47   ` Vladimir Davydov
2018-05-14  9:34     ` Kirill Tkhai
2018-05-15  3:54       ` Vladimir Davydov
2018-05-10  9:52 ` [PATCH v5 04/13] mm: Refactoring in workingset_init() Kirill Tkhai
2018-05-10  9:52 ` [PATCH v5 05/13] fs: Refactoring in alloc_super() Kirill Tkhai
2018-05-10  9:53 ` [PATCH v5 06/13] fs: Propagate shrinker::id to list_lru Kirill Tkhai
2018-05-13 16:57   ` Vladimir Davydov
2018-05-10  9:53 ` [PATCH v5 07/13] list_lru: Add memcg argument to list_lru_from_kmem() Kirill Tkhai
2018-05-10  9:53 ` [PATCH v5 08/13] list_lru: Pass dst_memcg argument to memcg_drain_list_lru_node() Kirill Tkhai
2018-05-10  9:53 ` [PATCH v5 09/13] list_lru: Pass lru " Kirill Tkhai
2018-05-10  9:53 ` [PATCH v5 10/13] mm: Set bit in memcg shrinker bitmap on first list_lru item apearance Kirill Tkhai
2018-05-15  4:08   ` Vladimir Davydov
2018-05-10  9:53 ` [PATCH v5 11/13] mm: Iterate only over charged shrinkers during memcg shrink_slab() Kirill Tkhai
2018-05-15  5:44   ` Vladimir Davydov
2018-05-15 10:12     ` Kirill Tkhai
2018-05-17  4:33       ` Vladimir Davydov
2018-05-17 11:39         ` Kirill Tkhai
2018-05-15 14:49     ` Kirill Tkhai
2018-05-17  4:16       ` Vladimir Davydov
2018-05-17 11:49         ` Kirill Tkhai
2018-05-17 13:51           ` Vladimir Davydov
2018-05-10  9:54 ` [PATCH v5 12/13] mm: Add SHRINK_EMPTY shrinker methods return value Kirill Tkhai
2018-05-10  9:54 ` [PATCH v5 13/13] mm: Clear shrinker bit if there are no objects related to memcg Kirill Tkhai
2018-05-15  5:59   ` Vladimir Davydov
2018-05-15  8:55     ` Kirill Tkhai
2018-05-17  4:49       ` Vladimir Davydov [this message]

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