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SubjectRe: [PATCH 2/4] mm: thp: make deferred split shrinker memcg aware
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On 6/10/19 1:21 AM, Kirill Tkhai wrote:
> Hi, Yang,
>
> On 07.06.2019 09:07, 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.
>>
>> And, move deleting THP from deferred split queue in page free before
>> memcg uncharge so that the page's memcg information is available.
>>
>> 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@virtuozzo.com>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.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/huge_mm.h | 15 ++++++++++
>> include/linux/memcontrol.h | 4 +++
>> include/linux/mm_types.h | 1 +
>> mm/huge_memory.c | 71 +++++++++++++++++++++++++++++++++-------------
>> mm/memcontrol.c | 19 +++++++++++++
>> mm/swap.c | 4 +++
>> 6 files changed, 94 insertions(+), 20 deletions(-)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 7cd5c15..8137c3a 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -250,6 +250,17 @@ 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;
>> +}
>> +
>> +extern void del_thp_from_deferred_split_queue(struct page *);
>> +
>> #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>> #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
>> #define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; })
>> @@ -368,6 +379,10 @@ static inline bool thp_migration_supported(void)
>> {
>> return false;
>> }
>> +
>> +static inline void del_thp_from_deferred_split_queue(struct page *page)
>> +{
>> +}
>> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>>
>> #endif /* _LINUX_HUGE_MM_H */
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index bc74d6a..5d3c10c 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -316,6 +316,10 @@ 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 8ec38b1..4eabf80 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 81cf759..3307697 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -492,10 +492,15 @@ 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)
>> +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;
> memory_cgrp_subsys is not early initialized, so at the beginning of boot
> root_mem_cgroup is NULL, and pages will use &pgdat->deferred_split_queue
> list head. But after root_mem_cgroup is initialized, another list head
> will be used, won't it?! So there will be two different list heads used
> for same cgroup.
>
> This may be a reason of a problem (I won't say you, where the problem will
> occur).

Actually I was wondering this too. But, it looks impossible. The memcg
is initialized by subsys_initcall, there are still fs, device and late
initcalls after it. The init process is run much later, so I can't think
of any THP could be put on deferred split queue before memcg is
initialized. There may be compound page allocation, i.e. skb, but we
don't care them.

>
>> }
>>
>> void prep_transhuge_page(struct page *page)
>> @@ -2658,7 +2663,7 @@ 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;
>> @@ -2792,25 +2797,36 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>> return ret;
>> }
>>
>> -void free_transhuge_page(struct page *page)
>> +void del_thp_from_deferred_split_queue(struct page *page)
>> {
>> - struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
>> - struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>> - unsigned long flags;
>> -
>> - spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>> - if (!list_empty(page_deferred_list(page))) {
>> - ds_queue->split_queue_len--;
>> - list_del(page_deferred_list(page));
>> + /*
>> + * The THP may be not on LRU at this point, e.g. the old page of
>> + * NUMA migration. And PageTransHuge is not enough to distinguish
>> + * with other compound page, e.g. skb, THP destructor is not used
>> + * anymore and will be removed, so the compound order sounds like
>> + * the only choice here.
>> + */
>> + if (PageTransHuge(page) && compound_order(page) == HPAGE_PMD_ORDER) {
>> + struct deferred_split *ds_queue = get_deferred_split_queue(page);
>> + unsigned long flags;
>> + spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>> + if (!list_empty(page_deferred_list(page))) {
>> + ds_queue->split_queue_len--;
>> + list_del(page_deferred_list(page));
>> + }
>> + spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
>> }
>> - spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
>> +}
>> +
>> +void free_transhuge_page(struct page *page)
>> +{
>> free_compound_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);
>> + struct mem_cgroup *memcg = compound_head(page)->mem_cgroup;
>> unsigned long flags;
>>
>> VM_BUG_ON_PAGE(!PageTransHuge(page), page);
>> @@ -2820,6 +2836,9 @@ void deferred_split_huge_page(struct page *page)
>> count_vm_event(THP_DEFERRED_SPLIT_PAGE);
>> list_add_tail(page_deferred_list(page), &ds_queue->split_queue);
>> ds_queue->split_queue_len++;
>> + if (memcg)
>> + memcg_set_shrinker_bit(memcg, page_to_nid(page),
>> + deferred_split_shrinker.id);
>> }
>> spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
>> }
>> @@ -2827,8 +2846,15 @@ 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);
>> - struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
>> + struct deferred_split *ds_queue;
>> +
>> + if (!sc->memcg) {
>> + struct pglist_data *pgdata = NODE_DATA(sc->nid);
>> + ds_queue = &pgdata->deferred_split_queue;
>> + return READ_ONCE(ds_queue->split_queue_len);
>> + }
>> +
>> + ds_queue = &sc->memcg->deferred_split_queue;
>> return READ_ONCE(ds_queue->split_queue_len);
>> }
>>
>> @@ -2836,12 +2862,17 @@ 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;
>>
>> + if (sc->memcg)
>> + ds_queue = &sc->memcg->deferred_split_queue;
>> + else
>> + ds_queue = &pgdata->deferred_split_queue;
>> +
>> 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 +2919,7 @@ 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,
>> };
>>
>> #ifdef CONFIG_DEBUG_FS
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index e50a2db..fe7e544 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -4579,6 +4579,11 @@ 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:
>> @@ -4949,6 +4954,20 @@ 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(page_deferred_list(page));
>> + from->deferred_split_queue.split_queue_len--;
>> + spin_unlock(&from->deferred_split_queue.split_queue_lock);
> Won't be better to assign
>
> page->mem_cgroup = to;
>
> after removing from one list and before linking to another list?
> There is possible no a problem, but another people writing code
> on top of this may not expect such the behavior.

It should be fine too.

>> + 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
>> /*
>> * It is safe to change page->mem_cgroup here because the page
>> * is referenced, charged, and isolated - we can't race with
>> diff --git a/mm/swap.c b/mm/swap.c
>> index 3a75722..3348295 100644
>> --- a/mm/swap.c
>> +++ b/mm/swap.c
>> @@ -69,6 +69,10 @@ static void __page_cache_release(struct page *page)
>> del_page_from_lru_list(page, lruvec, page_off_lru(page));
>> spin_unlock_irqrestore(&pgdat->lru_lock, flags);
>> }
>> +
>> + /* Delete THP from deferred split queue before memcg uncharge */
>> + del_thp_from_deferred_split_queue(page);
>> +
>> __ClearPageWaiters(page);
>> mem_cgroup_uncharge(page);
>> }

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