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SubjectRe: [v5 PATCH 4/4] mm: thp: make deferred split shrinker memcg aware
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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

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

>
> @@ -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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