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    SubjectRe: [PATCH v17 00/21] per memcg lru lock
    From
    Date
    From e2918c8fa741442255a2f12659f95dae94fdfe5d Mon Sep 17 00:00:00 2001
    From: Alex Shi <alex.shi@linux.alibaba.com>
    Date: Sat, 1 Aug 2020 22:49:31 +0800
    Subject: [PATCH 3/3] mm/swap.c: optimizing __pagevec_lru_add lru_lock

    The current relock will unlock/lock lru_lock with every time lruvec
    changes, so it would cause frequency relock if 2 memcgs are reading file
    simultaneously.

    This patch will record the involved lru_lock and only hold them once in
    above scenario. That could reduce the lock contention.

    Using per cpu data intead of local stack data to avoid repeatly
    INIT_LIST_HEAD action.

    [lkp@intel.com: found a build issue in the original patch, thanks]
    Suggested-by: Konstantin Khlebnikov <koct9i@gmail.com>
    Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: linux-mm@kvack.org
    Cc: linux-kernel@vger.kernel.org
    ---
    mm/swap.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++------
    1 file changed, 51 insertions(+), 6 deletions(-)

    diff --git a/mm/swap.c b/mm/swap.c
    index d88a6c650a7c..e227fec6983c 100644
    --- a/mm/swap.c
    +++ b/mm/swap.c
    @@ -72,6 +72,27 @@ static DEFINE_PER_CPU(struct lru_pvecs, lru_pvecs) = {
    .lock = INIT_LOCAL_LOCK(lock),
    };

    +struct pvlvs {
    + struct list_head lists[PAGEVEC_SIZE];
    + struct lruvec *vecs[PAGEVEC_SIZE];
    +};
    +static DEFINE_PER_CPU(struct pvlvs, pvlvs);
    +
    +static int __init pvlvs_init(void) {
    + int i, cpu;
    + struct pvlvs *pvecs;
    +
    + for (cpu = 0; cpu < NR_CPUS; cpu++) {
    + if (!cpu_possible(cpu))
    + continue;
    + pvecs = per_cpu_ptr(&pvlvs, cpu);
    + for (i = 0; i < PAGEVEC_SIZE; i++)
    + INIT_LIST_HEAD(&pvecs->lists[i]);
    + }
    + return 0;
    +}
    +subsys_initcall(pvlvs_init);
    +
    /*
    * This path almost never happens for VM activity - pages are normally
    * freed via pagevecs. But it gets used by networking.
    @@ -963,18 +984,42 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec)
    */
    void __pagevec_lru_add(struct pagevec *pvec)
    {
    - int i;
    + int i, j, total = 0;
    struct lruvec *lruvec = NULL;
    unsigned long flags = 0;
    + struct page *page;
    + struct pvlvs *lvs = this_cpu_ptr(&pvlvs);

    + /* Sort the same lruvec pages on a list. */
    for (i = 0; i < pagevec_count(pvec); i++) {
    - struct page *page = pvec->pages[i];
    + page = pvec->pages[i];
    + lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
    +
    + /* Try to find a same lruvec */
    + for (j = 0; j <= total; j++)
    + if (lruvec == lvs->vecs[j])
    + break;
    + /* A new lruvec */
    + if (j > total) {
    + lvs->vecs[total] = lruvec;
    + j = total;
    + total++;
    + }

    - lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
    - __pagevec_lru_add_fn(page, lruvec);
    + list_add(&page->lru, &lvs->lists[j]);
    }
    - if (lruvec)
    - unlock_page_lruvec_irqrestore(lruvec, flags);
    +
    + for (i = 0; i < total; i++) {
    + spin_lock_irqsave(&lvs->vecs[i]->lru_lock, flags);
    + while (!list_empty(&lvs->lists[i])) {
    + page = lru_to_page(&lvs->lists[i]);
    + list_del(&page->lru);
    + __pagevec_lru_add_fn(page, lvs->vecs[i]);
    + }
    + spin_unlock_irqrestore(&lvs->vecs[i]->lru_lock, flags);
    + lvs->vecs[i] = NULL;
    + }
    +
    release_pages(pvec->pages, pvec->nr);
    pagevec_reinit(pvec);
    }
    --
    1.8.3.1

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