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    Subject[PATCH v5 2/2] mm/memcontrol.c: Reduce reclaim retries in mem_cgroup_resize_limit()
    Date
    Currently mem_cgroup_resize_limit() retries to set limit after reclaiming
    32 pages. It makes more sense to reclaim needed amount of pages right away.

    This works noticeably faster, especially if 'usage - limit' big.
    E.g. bringing down limit from 4G to 50M:

    Before:
    # perf stat echo 50M > memory.limit_in_bytes

    Performance counter stats for 'echo 50M':

    386.582382 task-clock (msec) # 0.835 CPUs utilized
    2,502 context-switches # 0.006 M/sec

    0.463244382 seconds time elapsed

    After:
    # perf stat echo 50M > memory.limit_in_bytes

    Performance counter stats for 'echo 50M':

    169.403906 task-clock (msec) # 0.849 CPUs utilized
    14 context-switches # 0.083 K/sec

    0.199536900 seconds time elapsed

    Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
    Cc: Shakeel Butt <shakeelb@google.com>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
    ---
    mm/memcontrol.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 9d987f3e79dc..09bac2df2f12 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -2448,6 +2448,7 @@ static DEFINE_MUTEX(memcg_limit_mutex);
    static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
    unsigned long limit, bool memsw)
    {
    + unsigned long nr_pages;
    bool enlarge = false;
    int ret;
    bool limits_invariant;
    @@ -2479,8 +2480,9 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
    if (!ret)
    break;

    - if (!try_to_free_mem_cgroup_pages(memcg, 1,
    - GFP_KERNEL, !memsw)) {
    + nr_pages = max_t(long, 1, page_counter_read(counter) - limit);
    + if (!try_to_free_mem_cgroup_pages(memcg, nr_pages,
    + GFP_KERNEL, !memsw)) {
    ret = -EBUSY;
    break;
    }
    --
    2.13.6
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