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    Subject[PATCH] mm: workingset: fix vmstat counters for shadow nodes
    Date
    Memcg counters for shadow nodes are broken because the memcg pointer is
    obtained in a wrong way. The following approach is used:
    virt_to_page(xa_node)->mem_cgroup

    Since commit 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup
    pointer for slab pages") page->mem_cgroup pointer isn't set for slab pages,
    so memcg_from_slab_page() should be used instead.

    Also I doubt that it ever worked correctly: virt_to_head_page() should be
    used instead of virt_to_page(). Otherwise objects residing on tail pages
    are not accounted, because only the head page contains a valid mem_cgroup
    pointer. That was a case since the introduction of these counters by the
    commit 68d48e6a2df5 ("mm: workingset: add vmstat counter for shadow nodes").

    Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
    Signed-off-by: Roman Gushchin <guro@fb.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    ---
    include/linux/memcontrol.h | 19 +++++++++++++++++++
    mm/memcontrol.c | 20 ++++++++++++++++++++
    mm/workingset.c | 10 ++++------
    3 files changed, 43 insertions(+), 6 deletions(-)

    diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
    index 2cbce1fe7780..40f30ea30925 100644
    --- a/include/linux/memcontrol.h
    +++ b/include/linux/memcontrol.h
    @@ -683,6 +683,7 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,

    void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
    int val);
    +void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val);

    static inline void mod_lruvec_state(struct lruvec *lruvec,
    enum node_stat_item idx, int val)
    @@ -1098,6 +1099,14 @@ static inline void mod_lruvec_page_state(struct page *page,
    mod_node_page_state(page_pgdat(page), idx, val);
    }

    +static inline void __mod_lruvec_slab_state(void *p, enum node_stat_item idx,
    + int val)
    +{
    + struct page *page = virt_to_head_page(p);
    +
    + __mod_node_page_state(page_pgdat(page), idx, val);
    +}
    +
    static inline
    unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
    gfp_t gfp_mask,
    @@ -1185,6 +1194,16 @@ static inline void __dec_lruvec_page_state(struct page *page,
    __mod_lruvec_page_state(page, idx, -1);
    }

    +static inline void __inc_lruvec_slab_state(void *p, enum node_stat_item idx)
    +{
    + __mod_lruvec_slab_state(p, idx, 1);
    +}
    +
    +static inline void __dec_lruvec_slab_state(void *p, enum node_stat_item idx)
    +{
    + __mod_lruvec_slab_state(p, idx, -1);
    +}
    +
    /* idx can be of type enum memcg_stat_item or node_stat_item */
    static inline void inc_memcg_state(struct mem_cgroup *memcg,
    int idx)
    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 5c7b9facb0eb..4fca83d51134 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -769,6 +769,26 @@ void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
    __this_cpu_write(pn->lruvec_stat_cpu->count[idx], x);
    }

    +void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
    +{
    + struct page *page = virt_to_head_page(p);
    + pg_data_t *pgdat = page_pgdat(page);
    + struct mem_cgroup *memcg;
    + struct lruvec *lruvec;
    +
    + rcu_read_lock();
    + memcg = memcg_from_slab_page(page);
    +
    + /* Untracked pages have no memcg, no lruvec. Update only the node */
    + if (!memcg || memcg == root_mem_cgroup) {
    + __mod_node_page_state(pgdat, idx, val);
    + } else {
    + lruvec = mem_cgroup_lruvec(pgdat, memcg);
    + __mod_lruvec_state(lruvec, idx, val);
    + }
    + rcu_read_unlock();
    +}
    +
    /**
    * __count_memcg_events - account VM events in a cgroup
    * @memcg: the memory cgroup
    diff --git a/mm/workingset.c b/mm/workingset.c
    index e0b4edcb88c8..c963831d354f 100644
    --- a/mm/workingset.c
    +++ b/mm/workingset.c
    @@ -380,14 +380,12 @@ void workingset_update_node(struct xa_node *node)
    if (node->count && node->count == node->nr_values) {
    if (list_empty(&node->private_list)) {
    list_lru_add(&shadow_nodes, &node->private_list);
    - __inc_lruvec_page_state(virt_to_page(node),
    - WORKINGSET_NODES);
    + __inc_lruvec_slab_state(node, WORKINGSET_NODES);
    }
    } else {
    if (!list_empty(&node->private_list)) {
    list_lru_del(&shadow_nodes, &node->private_list);
    - __dec_lruvec_page_state(virt_to_page(node),
    - WORKINGSET_NODES);
    + __dec_lruvec_slab_state(node, WORKINGSET_NODES);
    }
    }
    }
    @@ -480,7 +478,7 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
    }

    list_lru_isolate(lru, item);
    - __dec_lruvec_page_state(virt_to_page(node), WORKINGSET_NODES);
    + __dec_lruvec_slab_state(node, WORKINGSET_NODES);

    spin_unlock(lru_lock);

    @@ -503,7 +501,7 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
    * shadow entries we were tracking ...
    */
    xas_store(&xas, NULL);
    - __inc_lruvec_page_state(virt_to_page(node), WORKINGSET_NODERECLAIM);
    + __inc_lruvec_slab_state(node, WORKINGSET_NODERECLAIM);

    out_invalid:
    xa_unlock_irq(&mapping->i_pages);
    --
    2.21.0
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