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    Subject[PATCH v2 13/13] mm: lru: use lruvec lock to serialize memcg changes
    Date
    As described by commit fc574c23558c ("mm/swap.c: serialize memcg
    changes in pagevec_lru_move_fn"), TestClearPageLRU() aims to
    serialize mem_cgroup_move_account() during pagevec_lru_move_fn().
    Now lock_page_lruvec*() has the ability to detect whether page
    memcg has been changed. So we can use lruvec lock to serialize
    mem_cgroup_move_account() during pagevec_lru_move_fn(). This
    change is a partial revert of the commit fc574c23558c ("mm/swap.c:
    serialize memcg changes in pagevec_lru_move_fn").

    And pagevec_lru_move_fn() is more hot compare with
    mem_cgroup_move_account(), removing an atomic operation would be
    an optimization. Also this change would not dirty cacheline for a
    page which isn't on the LRU.

    Signed-off-by: Muchun Song <songmuchun@bytedance.com>
    ---
    mm/compaction.c | 1 +
    mm/memcontrol.c | 31 +++++++++++++++++++++++++++++++
    mm/swap.c | 41 +++++++++++------------------------------
    mm/vmscan.c | 9 ++++-----
    4 files changed, 47 insertions(+), 35 deletions(-)

    diff --git a/mm/compaction.c b/mm/compaction.c
    index c4ba41de8591..9e74f96f9879 100644
    --- a/mm/compaction.c
    +++ b/mm/compaction.c
    @@ -529,6 +529,7 @@ static struct lruvec *compact_lock_page_irqsave(struct page *page,

    spin_lock_irqsave(&lruvec->lru_lock, *flags);
    out:
    + /* See the comments in lock_page_lruvec(). */
    if (unlikely(lruvec_memcg(lruvec) != page_memcg(page))) {
    spin_unlock_irqrestore(&lruvec->lru_lock, *flags);
    goto retry;
    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index e46fc01c6164..ab65d1c975cc 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -1298,12 +1298,38 @@ struct lruvec *lock_page_lruvec(struct page *page)
    lruvec = mem_cgroup_page_lruvec(page);
    spin_lock(&lruvec->lru_lock);

    + /*
    + * The memcg of the page can be changed by any the following routines:
    + *
    + * 1) mem_cgroup_move_account() or
    + * 2) memcg_reparent_objcgs()
    + *
    + * The possible bad scenario would like:
    + *
    + * CPU0: CPU1: CPU2:
    + * lruvec = mem_cgroup_page_lruvec()
    + *
    + * if (!isolate_lru_page())
    + * mem_cgroup_move_account()
    + *
    + * memcg_reparent_objcgs()
    + *
    + * spin_lock(&lruvec->lru_lock)
    + * ^^^^^^
    + * wrong lock
    + *
    + * Either CPU1 or CPU2 can change page memcg, so we need to check
    + * whether page memcg is changed, if so, we should reacquire the
    + * new lruvec lock.
    + */
    if (unlikely(lruvec_memcg(lruvec) != page_memcg(page))) {
    spin_unlock(&lruvec->lru_lock);
    goto retry;
    }

    /*
    + * When we reach here, it means that the page_memcg(page) is stable.
    + *
    * Preemption is disabled in the internal of spin_lock, which can serve
    * as RCU read-side critical sections.
    */
    @@ -1321,6 +1347,7 @@ struct lruvec *lock_page_lruvec_irq(struct page *page)
    lruvec = mem_cgroup_page_lruvec(page);
    spin_lock_irq(&lruvec->lru_lock);

    + /* See the comments in lock_page_lruvec(). */
    if (unlikely(lruvec_memcg(lruvec) != page_memcg(page))) {
    spin_unlock_irq(&lruvec->lru_lock);
    goto retry;
    @@ -1341,6 +1368,7 @@ struct lruvec *lock_page_lruvec_irqsave(struct page *page, unsigned long *flags)
    lruvec = mem_cgroup_page_lruvec(page);
    spin_lock_irqsave(&lruvec->lru_lock, *flags);

    + /* See the comments in lock_page_lruvec(). */
    if (unlikely(lruvec_memcg(lruvec) != page_memcg(page))) {
    spin_unlock_irqrestore(&lruvec->lru_lock, *flags);
    goto retry;
    @@ -5841,7 +5869,10 @@ static int mem_cgroup_move_account(struct page *page,
    obj_cgroup_get(to->objcg);
    obj_cgroup_put(from->objcg);

    + /* See the comments in lock_page_lruvec(). */
    + spin_lock(&from_vec->lru_lock);
    page->memcg_data = (unsigned long)to->objcg;
    + spin_unlock(&from_vec->lru_lock);

    __unlock_page_objcg(from->objcg);

    diff --git a/mm/swap.c b/mm/swap.c
    index 18d44f978b2e..fa2352f0f9d3 100644
    --- a/mm/swap.c
    +++ b/mm/swap.c
    @@ -189,14 +189,8 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
    for (i = 0; i < pagevec_count(pvec); i++) {
    struct page *page = pvec->pages[i];

    - /* block memcg migration during page moving between lru */
    - if (!TestClearPageLRU(page))
    - continue;
    -
    lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
    (*move_fn)(page, lruvec);
    -
    - SetPageLRU(page);
    }
    if (lruvec)
    unlock_page_lruvec_irqrestore(lruvec, flags);
    @@ -206,7 +200,7 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,

    static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec)
    {
    - if (!PageUnevictable(page)) {
    + if (PageLRU(page) && !PageUnevictable(page)) {
    del_page_from_lru_list(page, lruvec);
    ClearPageActive(page);
    add_page_to_lru_list_tail(page, lruvec);
    @@ -302,7 +296,7 @@ void lru_note_cost_page(struct page *page)

    static void __activate_page(struct page *page, struct lruvec *lruvec)
    {
    - if (!PageActive(page) && !PageUnevictable(page)) {
    + if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
    int nr_pages = thp_nr_pages(page);

    del_page_from_lru_list(page, lruvec);
    @@ -355,12 +349,9 @@ static void activate_page(struct page *page)
    struct lruvec *lruvec;

    page = compound_head(page);
    - if (TestClearPageLRU(page)) {
    - lruvec = lock_page_lruvec_irq(page);
    - __activate_page(page, lruvec);
    - unlock_page_lruvec_irq(lruvec);
    - SetPageLRU(page);
    - }
    + lruvec = lock_page_lruvec_irq(page);
    + __activate_page(page, lruvec);
    + unlock_page_lruvec_irq(lruvec);
    }
    #endif

    @@ -515,6 +506,9 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)
    bool active = PageActive(page);
    int nr_pages = thp_nr_pages(page);

    + if (!PageLRU(page))
    + return;
    +
    if (PageUnevictable(page))
    return;

    @@ -552,7 +546,7 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)

    static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)
    {
    - if (PageActive(page) && !PageUnevictable(page)) {
    + if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
    int nr_pages = thp_nr_pages(page);

    del_page_from_lru_list(page, lruvec);
    @@ -568,7 +562,7 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)

    static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec)
    {
    - if (PageAnon(page) && PageSwapBacked(page) &&
    + if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
    !PageSwapCache(page) && !PageUnevictable(page)) {
    int nr_pages = thp_nr_pages(page);

    @@ -1033,20 +1027,7 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec)
    */
    void __pagevec_lru_add(struct pagevec *pvec)
    {
    - int i;
    - struct lruvec *lruvec = NULL;
    - unsigned long flags = 0;
    -
    - for (i = 0; i < pagevec_count(pvec); i++) {
    - struct page *page = pvec->pages[i];
    -
    - lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
    - __pagevec_lru_add_fn(page, lruvec);
    - }
    - if (lruvec)
    - unlock_page_lruvec_irqrestore(lruvec, flags);
    - release_pages(pvec->pages, pvec->nr);
    - pagevec_reinit(pvec);
    + pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn);
    }

    /**
    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index f38ec21babf3..e9f4a2360465 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -4672,18 +4672,17 @@ void check_move_unevictable_pages(struct pagevec *pvec)
    nr_pages = thp_nr_pages(page);
    pgscanned += nr_pages;

    - /* block memcg migration during page moving between lru */
    - if (!TestClearPageLRU(page))
    + lruvec = relock_page_lruvec_irq(page, lruvec);
    +
    + if (!PageLRU(page) || !PageUnevictable(page))
    continue;

    - lruvec = relock_page_lruvec_irq(page, lruvec);
    - if (page_evictable(page) && PageUnevictable(page)) {
    + if (page_evictable(page)) {
    del_page_from_lru_list(page, lruvec);
    ClearPageUnevictable(page);
    add_page_to_lru_list(page, lruvec);
    pgrescued += nr_pages;
    }
    - SetPageLRU(page);
    }

    if (lruvec) {
    --
    2.11.0
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