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SubjectRe: [v5 PATCH 4/4] mm: thp: make deferred split shrinker memcg aware
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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@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>
>> Cc: Qian Cai <cai@lca.pw>
>> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.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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