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    SubjectRe: [PATCH 2/4] Memory controller soft limit interface (v3)
    On Sun, 01 Mar 2009 12:00:11 +0530
    Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

    >
    > From: Balbir Singh <balbir@linux.vnet.ibm.com>
    >
    > Changelog v2...v1
    > 1. Add support for res_counter_check_soft_limit_locked. This is used
    > by the hierarchy code.
    >
    > Add an interface to allow get/set of soft limits. Soft limits for memory plus
    > swap controller (memsw) is currently not supported. Resource counters have
    > been enhanced to support soft limits and new type RES_SOFT_LIMIT has been
    > added. Unlike hard limits, soft limits can be directly set and do not
    > need any reclaim or checks before setting them to a newer value.
    >
    > Kamezawa-San raised a question as to whether soft limit should belong
    > to res_counter. Since all resources understand the basic concepts of
    > hard and soft limits, it is justified to add soft limits here. Soft limits
    > are a generic resource usage feature, even file system quotas support
    > soft limits.
    >
    I don't convice adding more logics to res_counter is a good to do, yet.


    Thanks,
    -Kame



    > Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    > ---
    >
    > include/linux/res_counter.h | 47 +++++++++++++++++++++++++++++++++++++++++++
    > kernel/res_counter.c | 3 +++
    > mm/memcontrol.c | 20 ++++++++++++++++++
    > 3 files changed, 70 insertions(+), 0 deletions(-)
    >
    >
    > diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
    > index 4c5bcf6..b5f14fa 100644
    > --- a/include/linux/res_counter.h
    > +++ b/include/linux/res_counter.h
    > @@ -35,6 +35,10 @@ struct res_counter {
    > */
    > unsigned long long limit;
    > /*
    > + * the limit that usage can be exceed
    > + */
    > + unsigned long long soft_limit;
    > + /*
    > * the number of unsuccessful attempts to consume the resource
    > */
    > unsigned long long failcnt;
    > @@ -85,6 +89,7 @@ enum {
    > RES_MAX_USAGE,
    > RES_LIMIT,
    > RES_FAILCNT,
    > + RES_SOFT_LIMIT,
    > };
    >
    > /*
    > @@ -130,6 +135,36 @@ static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
    > return false;
    > }
    >
    > +static inline bool res_counter_soft_limit_check_locked(struct res_counter *cnt)
    > +{
    > + if (cnt->usage < cnt->soft_limit)
    > + return true;
    > +
    > + return false;
    > +}
    > +
    > +/**
    > + * Get the difference between the usage and the soft limit
    > + * @cnt: The counter
    > + *
    > + * Returns 0 if usage is less than or equal to soft limit
    > + * The difference between usage and soft limit, otherwise.
    > + */
    > +static inline unsigned long long
    > +res_counter_soft_limit_excess(struct res_counter *cnt)
    > +{
    > + unsigned long long excess;
    > + unsigned long flags;
    > +
    > + spin_lock_irqsave(&cnt->lock, flags);
    > + if (cnt->usage <= cnt->soft_limit)
    > + excess = 0;
    > + else
    > + excess = cnt->usage - cnt->soft_limit;
    > + spin_unlock_irqrestore(&cnt->lock, flags);
    > + return excess;
    > +}
    > +
    > /*
    > * Helper function to detect if the cgroup is within it's limit or
    > * not. It's currently called from cgroup_rss_prepare()
    > @@ -178,4 +213,16 @@ static inline int res_counter_set_limit(struct res_counter *cnt,
    > return ret;
    > }
    >
    > +static inline int
    > +res_counter_set_soft_limit(struct res_counter *cnt,
    > + unsigned long long soft_limit)
    > +{
    > + unsigned long flags;
    > +
    > + spin_lock_irqsave(&cnt->lock, flags);
    > + cnt->soft_limit = soft_limit;
    > + spin_unlock_irqrestore(&cnt->lock, flags);
    > + return 0;
    > +}
    > +
    > #endif
    > diff --git a/kernel/res_counter.c b/kernel/res_counter.c
    > index bf8e753..4e6dafe 100644
    > --- a/kernel/res_counter.c
    > +++ b/kernel/res_counter.c
    > @@ -19,6 +19,7 @@ void res_counter_init(struct res_counter *counter, struct res_counter *parent)
    > {
    > spin_lock_init(&counter->lock);
    > counter->limit = (unsigned long long)LLONG_MAX;
    > + counter->soft_limit = (unsigned long long)LLONG_MAX;
    > counter->parent = parent;
    > }
    >
    > @@ -101,6 +102,8 @@ res_counter_member(struct res_counter *counter, int member)
    > return &counter->limit;
    > case RES_FAILCNT:
    > return &counter->failcnt;
    > + case RES_SOFT_LIMIT:
    > + return &counter->soft_limit;
    > };
    >
    > BUG();
    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index 7bb14fd..75a7b1a 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -1939,6 +1939,20 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
    > else
    > ret = mem_cgroup_resize_memsw_limit(memcg, val);
    > break;
    > + case RES_SOFT_LIMIT:
    > + ret = res_counter_memparse_write_strategy(buffer, &val);
    > + if (ret)
    > + break;
    > + /*
    > + * For memsw, soft limits are hard to implement in terms
    > + * of semantics, for now, we support soft limits for
    > + * control without swap
    > + */
    > + if (type == _MEM)
    > + ret = res_counter_set_soft_limit(&memcg->res, val);
    > + else
    > + ret = -EINVAL;
    > + break;
    > default:
    > ret = -EINVAL; /* should be BUG() ? */
    > break;
    > @@ -2188,6 +2202,12 @@ static struct cftype mem_cgroup_files[] = {
    > .read_u64 = mem_cgroup_read,
    > },
    > {
    > + .name = "soft_limit_in_bytes",
    > + .private = MEMFILE_PRIVATE(_MEM, RES_SOFT_LIMIT),
    > + .write_string = mem_cgroup_write,
    > + .read_u64 = mem_cgroup_read,
    > + },
    > + {
    > .name = "failcnt",
    > .private = MEMFILE_PRIVATE(_MEM, RES_FAILCNT),
    > .trigger = mem_cgroup_reset,
    >
    > --
    > Balbir
    > --
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