Re: [PATCH] mm: thp: move deferred split queue to memcg's nodeinfo

[Yang Shi <yang.shi@linux.alibaba.com>]

On 10/2/19 1:43 AM, Michal Hocko wrote:
> On Wed 02-10-19 06:16:43, Yang Shi wrote:
>> The commit 87eaceb3faa59b9b4d940ec9554ce251325d83fe ("mm: thp: make
>> deferred split shrinker memcg aware") makes deferred split queue per
>> memcg to resolve memcg pre-mature OOM problem.  But, all nodes end up
>> sharing the same queue instead of one queue per-node before the commit.
>> It is not a big deal for memcg limit reclaim, but it may cause global
>> kswapd shrink THPs from a different node.
>>
>> And, 0-day testing reported -19.6% regression of stress-ng's madvise
>> test [1].  I didn't see that much regression on my test box (24 threads,
>> 48GB memory, 2 nodes), with the same test (stress-ng --timeout 1
>> --metrics-brief --sequential 72  --class vm --exclude spawn,exec), I saw
>> average -3% (run the same test 10 times then calculate the average since
>> the test itself may have most 15% variation according to my test)
>> regression sometimes (not every time, sometimes I didn't see regression
>> at all).
>>
>> This might be caused by deferred split queue lock contention.  With some
>> configuration (i.e. just one root memcg) the lock contention my be worse
>> than before (given 2 nodes, two locks are reduced to one lock).
>>
>> So, moving deferred split queue to memcg's nodeinfo to make it NUMA
>> aware again.
>>
>> With this change stress-ng's madvise test shows average 4% improvement
>> sometimes and I didn't see degradation anymore.
> My concern about this getting more and more complex
> (http://lkml.kernel.org/r/20191002084014.GH15624@dhcp22.suse.cz) holds
> here even more. Can we step back and reconsider the whole thing please?

I'm not intended to make this more complicated, but this patch is aimed 
to fix the NUMA awareness issue. It doesn't tune something further.

>
>> [1]: https://lore.kernel.org/lkml/20190930084604.GC17687@shao2-debian/
>>
>> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Hugh Dickins <hughd@google.com>
>> Cc: Shakeel Butt <shakeelb@google.com>
>> Cc: David Rientjes <rientjes@google.com>
>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>> ---
>>   include/linux/memcontrol.h |  8 ++++----
>>   mm/huge_memory.c           | 15 +++++++++------
>>   mm/memcontrol.c            | 29 +++++++++++++++++------------
>>   3 files changed, 30 insertions(+), 22 deletions(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 9b60863..4b5c791 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -137,6 +137,10 @@ struct mem_cgroup_per_node {
>>   	bool			congested;	/* memcg has many dirty pages */
>>   						/* backed by a congested BDI */
>>   
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> +	struct deferred_split deferred_split_queue;
>> +#endif
>> +
>>   	struct mem_cgroup	*memcg;		/* Back pointer, we cannot */
>>   						/* use container_of	   */
>>   };
>> @@ -330,10 +334,6 @@ struct mem_cgroup {
>>   	struct list_head event_list;
>>   	spinlock_t event_list_lock;
>>   
>> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> -	struct deferred_split deferred_split_queue;
>> -#endif
>> -
>>   	struct mem_cgroup_per_node *nodeinfo[0];
>>   	/* WARNING: nodeinfo must be the last member here */
>>   };
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index c5cb6dc..3b78910 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -500,10 +500,11 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
>>   static inline struct deferred_split *get_deferred_split_queue(struct page *page)
>>   {
>>   	struct mem_cgroup *memcg = compound_head(page)->mem_cgroup;
>> -	struct pglist_data *pgdat = NODE_DATA(page_to_nid(page));
>> +	int nid = page_to_nid(page);
>> +	struct pglist_data *pgdat = NODE_DATA(nid);
>>   
>>   	if (memcg)
>> -		return &memcg->deferred_split_queue;
>> +		return &memcg->nodeinfo[nid]->deferred_split_queue;
>>   	else
>>   		return &pgdat->deferred_split_queue;
>>   }
>> @@ -2882,12 +2883,13 @@ void deferred_split_huge_page(struct page *page)
>>   static unsigned long deferred_split_count(struct shrinker *shrink,
>>   		struct shrink_control *sc)
>>   {
>> -	struct pglist_data *pgdata = NODE_DATA(sc->nid);
>> +	int nid = sc->nid;
>> +	struct pglist_data *pgdata = NODE_DATA(nid);
>>   	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>>   
>>   #ifdef CONFIG_MEMCG
>>   	if (sc->memcg)
>> -		ds_queue = &sc->memcg->deferred_split_queue;
>> +		ds_queue = &sc->memcg->nodeinfo[nid]->deferred_split_queue;
>>   #endif
>>   	return READ_ONCE(ds_queue->split_queue_len);
>>   }
>> @@ -2895,7 +2897,8 @@ static unsigned long deferred_split_count(struct shrinker *shrink,
>>   static unsigned long deferred_split_scan(struct shrinker *shrink,
>>   		struct shrink_control *sc)
>>   {
>> -	struct pglist_data *pgdata = NODE_DATA(sc->nid);
>> +	int nid = sc->nid;
>> +	struct pglist_data *pgdata = NODE_DATA(nid);
>>   	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>>   	unsigned long flags;
>>   	LIST_HEAD(list), *pos, *next;
>> @@ -2904,7 +2907,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>>   
>>   #ifdef CONFIG_MEMCG
>>   	if (sc->memcg)
>> -		ds_queue = &sc->memcg->deferred_split_queue;
>> +		ds_queue = &sc->memcg->nodeinfo[nid]->deferred_split_queue;
>>   #endif
>>   
>>   	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index c313c49..19d4295 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -4989,6 +4989,12 @@ static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
>>   	pn->on_tree = false;
>>   	pn->memcg = memcg;
>>   
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> +	spin_lock_init(&pn->deferred_split_queue.split_queue_lock);
>> +	INIT_LIST_HEAD(&pn->deferred_split_queue.split_queue);
>> +	pn->deferred_split_queue.split_queue_len = 0;
>> +#endif
>> +
>>   	memcg->nodeinfo[node] = pn;
>>   	return 0;
>>   }
>> @@ -5081,11 +5087,6 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
>>   		memcg->cgwb_frn[i].done =
>>   			__WB_COMPLETION_INIT(&memcg_cgwb_frn_waitq);
>>   #endif
>> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> -	spin_lock_init(&memcg->deferred_split_queue.split_queue_lock);
>> -	INIT_LIST_HEAD(&memcg->deferred_split_queue.split_queue);
>> -	memcg->deferred_split_queue.split_queue_len = 0;
>> -#endif
>>   	idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
>>   	return memcg;
>>   fail:
>> @@ -5419,6 +5420,8 @@ static int mem_cgroup_move_account(struct page *page,
>>   	unsigned int nr_pages = compound ? hpage_nr_pages(page) : 1;
>>   	int ret;
>>   	bool anon;
>> +	struct deferred_split *ds_queue;
>> +	int nid = page_to_nid(page);
>>   
>>   	VM_BUG_ON(from == to);
>>   	VM_BUG_ON_PAGE(PageLRU(page), page);
>> @@ -5466,10 +5469,11 @@ static int mem_cgroup_move_account(struct page *page,
>>   
>>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>   	if (compound && !list_empty(page_deferred_list(page))) {
>> -		spin_lock(&from->deferred_split_queue.split_queue_lock);
>> +		ds_queue = &from->nodeinfo[nid]->deferred_split_queue;
>> +		spin_lock(&ds_queue->split_queue_lock);
>>   		list_del_init(page_deferred_list(page));
>> -		from->deferred_split_queue.split_queue_len--;
>> -		spin_unlock(&from->deferred_split_queue.split_queue_lock);
>> +		ds_queue->split_queue_len--;
>> +		spin_unlock(&ds_queue->split_queue_lock);
>>   	}
>>   #endif
>>   	/*
>> @@ -5483,11 +5487,12 @@ static int mem_cgroup_move_account(struct page *page,
>>   
>>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>   	if (compound && list_empty(page_deferred_list(page))) {
>> -		spin_lock(&to->deferred_split_queue.split_queue_lock);
>> +		ds_queue = &to->nodeinfo[nid]->deferred_split_queue;
>> +		spin_lock(&ds_queue->split_queue_lock);
>>   		list_add_tail(page_deferred_list(page),
>> -			      &to->deferred_split_queue.split_queue);
>> -		to->deferred_split_queue.split_queue_len++;
>> -		spin_unlock(&to->deferred_split_queue.split_queue_lock);
>> +			      &ds_queue->split_queue);
>> +		ds_queue->split_queue_len++;
>> +		spin_unlock(&ds_queue->split_queue_lock);
>>   	}
>>   #endif
>>   
>> -- 
>> 1.8.3.1