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    Subject[PATCH] mm/memcg: add MAX_CHARGE_BATCH to limit unnecessary charge overhead
    Date
    From: Wanpeng Li <liwp@linux.vnet.ibm.com>

    Since exceeded unused cached charges would add pressure to
    mem_cgroup_do_charge, more overhead would burn cpu cycles when
    mem_cgroup_do_charge cause page reclaim or even OOM be triggered
    just for such exceeded unused cached charges. Add MAX_CHARGE_BATCH
    to limit max cached charges.

    Signed-off-by: Wanpeng Li <liwp.linux@gmail.com>
    ---
    mm/memcontrol.c | 16 ++++++++++++++++
    1 file changed, 16 insertions(+)

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 0e092eb..1ff317a 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -1954,6 +1954,14 @@ void mem_cgroup_update_page_stat(struct page *page,
    * TODO: maybe necessary to use big numbers in big irons.
    */
    #define CHARGE_BATCH 32U
    +
    +/*
    + * Max size of charge stock. Since exceeded unused cached charges would
    + * add pressure to mem_cgroup_do_charge which will cause page reclaim or
    + * even oom be triggered.
    + */
    +#define MAX_CHARGE_BATCH 1024U
    +
    struct memcg_stock_pcp {
    struct mem_cgroup *cached; /* this never be root cgroup */
    unsigned int nr_pages;
    @@ -2250,6 +2258,7 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
    unsigned int batch = max(CHARGE_BATCH, nr_pages);
    int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
    struct mem_cgroup *memcg = NULL;
    + struct memcg_stock_pcp *stock;
    int ret;

    /*
    @@ -2320,6 +2329,13 @@ again:
    rcu_read_unlock();
    }

    + stock = &get_cpu_var(memcg_stock);
    + if (memcg == stock->cached && stock->nr_pages) {
    + if (stock->nr_pages > MAX_CHARGE_BATCH)
    + batch = nr_pages;
    + }
    + put_cpu_var(memcg_stock);
    +
    do {
    bool oom_check;

    --
    1.7.9.5


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