Message-ID: <17b99fc9-552f-56ae-15f1-ba290f49b492@linux.alibaba.com>
Date:   Tue, 20 Aug 2019 09:10:41 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>,
        kirill.shutemov@...ux.intel.com, hannes@...xchg.org,
        mhocko@...e.com, hughd@...gle.com, shakeelb@...gle.com,
        rientjes@...gle.com, cai@....pw, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v5 PATCH 4/4] mm: thp: make deferred split shrinker memcg aware



On 8/20/19 4:06 AM, Kirill Tkhai wrote:
> On 07.08.2019 05:17, Yang Shi wrote:
>> Currently THP deferred split shrinker is not memcg aware, this may cause
>> premature OOM with some configuration. For example the below test would
>> run into premature OOM easily:
>>
>> $ cgcreate -g memory:thp
>> $ echo 4G > /sys/fs/cgroup/memory/thp/memory/limit_in_bytes
>> $ cgexec -g memory:thp transhuge-stress 4000
>>
>> transhuge-stress comes from kernel selftest.
>>
>> It is easy to hit OOM, but there are still a lot THP on the deferred
>> split queue, memcg direct reclaim can't touch them since the deferred
>> split shrinker is not memcg aware.
>>
>> Convert deferred split shrinker memcg aware by introducing per memcg
>> deferred split queue.  The THP should be on either per node or per memcg
>> deferred split queue if it belongs to a memcg.  When the page is
>> immigrated to the other memcg, it will be immigrated to the target
>> memcg's deferred split queue too.
>>
>> Reuse the second tail page's deferred_list for per memcg list since the
>> same THP can't be on multiple deferred split queues.
>>
>> Cc: Kirill Tkhai <ktkhai@...tuozzo.com>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
>> Cc: Hugh Dickins <hughd@...gle.com>
>> Cc: Shakeel Butt <shakeelb@...gle.com>
>> Cc: David Rientjes <rientjes@...gle.com>
>> Cc: Qian Cai <cai@....pw>
>> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> Reviewed-by: Kirill Tkhai <ktkhai@...tuozzo.com>
>
> But, please, see below one small suggestion.
>
>> ---
>>   include/linux/huge_mm.h    |  9 ++++++
>>   include/linux/memcontrol.h |  4 +++
>>   include/linux/mm_types.h   |  1 +
>>   mm/huge_memory.c           | 76 +++++++++++++++++++++++++++++++++++++++-------
>>   mm/memcontrol.c            | 24 +++++++++++++++
>>   5 files changed, 103 insertions(+), 11 deletions(-)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 45ede62..61c9ffd 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -267,6 +267,15 @@ static inline bool thp_migration_supported(void)
>>   	return IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION);
>>   }
>>   
>> +static inline struct list_head *page_deferred_list(struct page *page)
>> +{
>> +	/*
>> +	 * Global or memcg deferred list in the second tail pages is
>> +	 * occupied by compound_head.
>> +	 */
>> +	return &page[2].deferred_list;
>> +}
>> +
>>   #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>>   #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
>>   #define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; })
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 5771816..cace365 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -312,6 +312,10 @@ 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/include/linux/mm_types.h b/include/linux/mm_types.h
>> index 3a37a89..156640c 100644
>> --- a/include/linux/mm_types.h
>> +++ b/include/linux/mm_types.h
>> @@ -139,6 +139,7 @@ struct page {
>>   		struct {	/* Second tail page of compound page */
>>   			unsigned long _compound_pad_1;	/* compound_head */
>>   			unsigned long _compound_pad_2;
>> +			/* For both global and memcg */
>>   			struct list_head deferred_list;
>>   		};
>>   		struct {	/* Page table pages */
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index e0d8e08..c9a596e 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -495,11 +495,25 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
>>   	return pmd;
>>   }
>>   
>> -static inline struct list_head *page_deferred_list(struct page *page)
>> +#ifdef CONFIG_MEMCG
>> +static inline struct deferred_split *get_deferred_split_queue(struct page *page)
>>   {
>> -	/* ->lru in the tail pages is occupied by compound_head. */
>> -	return &page[2].deferred_list;
>> +	struct mem_cgroup *memcg = compound_head(page)->mem_cgroup;
>> +	struct pglist_data *pgdat = NODE_DATA(page_to_nid(page));
>> +
>> +	if (memcg)
>> +		return &memcg->deferred_split_queue;
>> +	else
>> +		return &pgdat->deferred_split_queue;
>> +}
>> +#else
>> +static inline struct deferred_split *get_deferred_split_queue(struct page *page)
>> +{
>> +	struct pglist_data *pgdat = NODE_DATA(page_to_nid(page));
>> +
>> +	return &pgdat->deferred_split_queue;
>>   }
>> +#endif
>>   
>>   void prep_transhuge_page(struct page *page)
>>   {
>> @@ -2658,7 +2672,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>>   {
>>   	struct page *head = compound_head(page);
>>   	struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
>> -	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>> +	struct deferred_split *ds_queue = get_deferred_split_queue(page);
>>   	struct anon_vma *anon_vma = NULL;
>>   	struct address_space *mapping = NULL;
>>   	int count, mapcount, extra_pins, ret;
>> @@ -2794,8 +2808,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>>   
>>   void free_transhuge_page(struct page *page)
>>   {
>> -	struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
>> -	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>> +	struct deferred_split *ds_queue = get_deferred_split_queue(page);
>>   	unsigned long flags;
>>   
>>   	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>> @@ -2809,17 +2822,37 @@ void free_transhuge_page(struct page *page)
>>   
>>   void deferred_split_huge_page(struct page *page)
>>   {
>> -	struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
>> -	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>> +	struct deferred_split *ds_queue = get_deferred_split_queue(page);
>> +#ifdef CONFIG_MEMCG
>> +	struct mem_cgroup *memcg = compound_head(page)->mem_cgroup;
>> +#endif
>>   	unsigned long flags;
>>   
>>   	VM_BUG_ON_PAGE(!PageTransHuge(page), page);
>>   
>> +	/*
>> +	 * The try_to_unmap() in page reclaim path might reach here too,
>> +	 * this may cause a race condition to corrupt deferred split queue.
>> +	 * And, if page reclaim is already handling the same page, it is
>> +	 * unnecessary to handle it again in shrinker.
>> +	 *
>> +	 * Check PageSwapCache to determine if the page is being
>> +	 * handled by page reclaim since THP swap would add the page into
>> +	 * swap cache before calling try_to_unmap().
>> +	 */
>> +	if (PageSwapCache(page))
>> +		return;
>> +
>>   	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>>   	if (list_empty(page_deferred_list(page))) {
>>   		count_vm_event(THP_DEFERRED_SPLIT_PAGE);
>>   		list_add_tail(page_deferred_list(page), &ds_queue->split_queue);
>>   		ds_queue->split_queue_len++;
>> +#ifdef CONFIG_MEMCG
>> +		if (memcg)
>> +			memcg_set_shrinker_bit(memcg, page_to_nid(page),
>> +					       deferred_split_shrinker.id);
>> +#endif
>>   	}
>>   	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
>>   }
>> @@ -2827,8 +2860,19 @@ void deferred_split_huge_page(struct page *page)
>>   static unsigned long deferred_split_count(struct shrinker *shrink,
>>   		struct shrink_control *sc)
>>   {
>> +	struct deferred_split *ds_queue;
>>   	struct pglist_data *pgdata = NODE_DATA(sc->nid);
>> -	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>> +
>> +#ifdef CONFIG_MEMCG
>> +	if (!sc->memcg) {
>> +		ds_queue = &pgdata->deferred_split_queue;
>> +		return READ_ONCE(ds_queue->split_queue_len);
>> +	}
>> +
>> +	ds_queue = &sc->memcg->deferred_split_queue;
>> +#else
>> +	ds_queue = &pgdata->deferred_split_queue;
>> +#endif
>>   	return READ_ONCE(ds_queue->split_queue_len);
>>   }
> Can we write this a little more compact?
>
> 	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>
> #ifdef CONFIG_MEMCG
> 	if (sc->memcg)
> 		ds_queue = &sc->memcg->deferred_split_queue;
> #endif

Yes, sure.

>
> Or just introduce a helper (something like get_sc_deferred_split_queue).
> The same is in .scan method.

A helper sounds fine too, but IMHO I don't see to much benefit since 
just _count and _scan would call them.

>
>>   
>> @@ -2836,12 +2880,21 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>>   		struct shrink_control *sc)
>>   {
>>   	struct pglist_data *pgdata = NODE_DATA(sc->nid);
>> -	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>> +	struct deferred_split *ds_queue;
>>   	unsigned long flags;
>>   	LIST_HEAD(list), *pos, *next;
>>   	struct page *page;
>>   	int split = 0;
>>   
>> +#ifdef CONFIG_MEMCG
>> +	if (sc->memcg)
>> +		ds_queue = &sc->memcg->deferred_split_queue;
>> +	else
>> +		ds_queue = &pgdata->deferred_split_queue;
>> +#else
>> +	ds_queue = &pgdata->deferred_split_queue;
>> +#endif
>> +
>>   	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>>   	/* Take pin on all head pages to avoid freeing them under us */
>>   	list_for_each_safe(pos, next, &ds_queue->split_queue) {
>> @@ -2888,7 +2941,8 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>>   	.count_objects = deferred_split_count,
>>   	.scan_objects = deferred_split_scan,
>>   	.seeks = DEFAULT_SEEKS,
>> -	.flags = SHRINKER_NUMA_AWARE,
>> +	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE |
>> +		 SHRINKER_NONSLAB,
>>   };
>>   
>>   #ifdef CONFIG_DEBUG_FS
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index d90ded1..da4a411 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -4698,6 +4698,11 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
>>   #ifdef CONFIG_CGROUP_WRITEBACK
>>   	INIT_LIST_HEAD(&memcg->cgwb_list);
>>   #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:
>> @@ -5071,6 +5076,14 @@ static int mem_cgroup_move_account(struct page *page,
>>   		__mod_memcg_state(to, NR_WRITEBACK, nr_pages);
>>   	}
>>   
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> +	if (compound && !list_empty(page_deferred_list(page))) {
>> +		spin_lock(&from->deferred_split_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);
>> +	}
>> +#endif
>>   	/*
>>   	 * It is safe to change page->mem_cgroup here because the page
>>   	 * is referenced, charged, and isolated - we can't race with
>> @@ -5079,6 +5092,17 @@ static int mem_cgroup_move_account(struct page *page,
>>   
>>   	/* caller should have done css_get */
>>   	page->mem_cgroup = to;
>> +
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> +	if (compound && list_empty(page_deferred_list(page))) {
>> +		spin_lock(&to->deferred_split_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);
>> +	}
>> +#endif
>> +
>>   	spin_unlock_irqrestore(&from->move_lock, flags);
>>   
>>   	ret = 0;
>>

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