fq_codel: add memory limitation per queue

On small embedded routers, one wants to control maximal amount of
memory used by fq_codel, instead of controlling number of packets or
bytes, since GRO/TSO make these not practical.

Assuming skb->truesize is accurate, we have to keep track of
skb->truesize sum for skbs in queue.

This patch adds a new TCA_FQ_CODEL_MEMORY_LIMIT attribute.

I chose a default value of 32 MBytes, which looks reasonable even
for heavy duty usages. (Prior fq_codel users should not be hurt
when they upgrade their kernels)

Two fields are added to tc_fq_codel_qd_stats to report :
 - Current memory usage
 - Number of drops caused by memory limits

# tc qd replace dev eth1 root est 1sec 4sec fq_codel memory_limit 4M
..
# tc -s -d qd sh dev eth1
qdisc fq_codel 8008: root refcnt 257 limit 10240p flows 1024
 quantum 1514 target 5.0ms interval 100.0ms memory_limit 4Mb ecn
 Sent 2083566791363 bytes 1376214889 pkt (dropped 4994406, overlimits 0
requeues 21705223)
 rate 9841Mbit 812549pps backlog 3906120b 376p requeues 21705223
  maxpacket 68130 drop_overlimit 4994406 new_flow_count 28855414
  ecn_mark 0 memory_used 4190048 drop_overmemory 4994406
  new_flows_len 1 old_flows_len 177

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Dave Täht <dave.taht@gmail.com>
Cc: Sebastian Möller <moeller0@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index a11afec..2382eed 100644 (file)
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -719,6 +719,7 @@ enum {
        TCA_FQ_CODEL_QUANTUM,
        TCA_FQ_CODEL_CE_THRESHOLD,
        TCA_FQ_CODEL_DROP_BATCH_SIZE,
+       TCA_FQ_CODEL_MEMORY_LIMIT,
        __TCA_FQ_CODEL_MAX
 };
 
@@ -743,6 +744,8 @@ struct tc_fq_codel_qd_stats {
        __u32   new_flows_len;  /* count of flows in new list */
        __u32   old_flows_len;  /* count of flows in old list */
        __u32   ce_mark;        /* packets above ce_threshold */
+       __u32   memory_usage;   /* in bytes */
+       __u32   drop_overmemory;
 };
 
 struct tc_fq_codel_cl_stats {

diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index e7b42b0..bb8bd93 100644 (file)
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -60,8 +60,11 @@ struct fq_codel_sched_data {
        u32             perturbation;   /* hash perturbation */
        u32             quantum;        /* psched_mtu(qdisc_dev(sch)); */
        u32             drop_batch_size;
+       u32             memory_limit;
        struct codel_params cparams;
        struct codel_stats cstats;
+       u32             memory_usage;
+       u32             drop_overmemory;
        u32             drop_overlimit;
        u32             new_flow_count;
 
@@ -143,6 +146,7 @@ static unsigned int fq_codel_drop(struct Qdisc *sch, unsigned int max_packets)
        unsigned int maxbacklog = 0, idx = 0, i, len;
        struct fq_codel_flow *flow;
        unsigned int threshold;
+       unsigned int mem = 0;
 
        /* Queue is full! Find the fat flow and drop packet(s) from it.
         * This might sound expensive, but with 1024 flows, we scan
@@ -167,11 +171,13 @@ static unsigned int fq_codel_drop(struct Qdisc *sch, unsigned int max_packets)
        do {
                skb = dequeue_head(flow);
                len += qdisc_pkt_len(skb);
+               mem += skb->truesize;
                kfree_skb(skb);
        } while (++i < max_packets && len < threshold);
 
        flow->dropped += i;
        q->backlogs[idx] -= len;
+       q->memory_usage -= mem;
        sch->qstats.drops += i;
        sch->qstats.backlog -= len;
        sch->q.qlen -= i;
@@ -193,6 +199,7 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
        unsigned int idx, prev_backlog, prev_qlen;
        struct fq_codel_flow *flow;
        int uninitialized_var(ret);
+       bool memory_limited;
 
        idx = fq_codel_classify(skb, sch, &ret);
        if (idx == 0) {
@@ -215,7 +222,9 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
                flow->deficit = q->quantum;
                flow->dropped = 0;
        }
-       if (++sch->q.qlen <= sch->limit)
+       q->memory_usage += skb->truesize;
+       memory_limited = q->memory_usage > q->memory_limit;
+       if (++sch->q.qlen <= sch->limit && !memory_limited)
                return NET_XMIT_SUCCESS;
 
        prev_backlog = sch->qstats.backlog;
@@ -229,7 +238,8 @@ static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
        ret = fq_codel_drop(sch, q->drop_batch_size);
 
        q->drop_overlimit += prev_qlen - sch->q.qlen;
-
+       if (memory_limited)
+               q->drop_overmemory += prev_qlen - sch->q.qlen;
        /* As we dropped packet(s), better let upper stack know this */
        qdisc_tree_reduce_backlog(sch, prev_qlen - sch->q.qlen,
                                  prev_backlog - sch->qstats.backlog);
@@ -308,6 +318,7 @@ begin:
                        list_del_init(&flow->flowchain);
                goto begin;
        }
+       q->memory_usage -= skb->truesize;
        qdisc_bstats_update(sch, skb);
        flow->deficit -= qdisc_pkt_len(skb);
        /* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
@@ -355,6 +366,7 @@ static const struct nla_policy fq_codel_policy[TCA_FQ_CODEL_MAX + 1] = {
        [TCA_FQ_CODEL_QUANTUM]  = { .type = NLA_U32 },
        [TCA_FQ_CODEL_CE_THRESHOLD] = { .type = NLA_U32 },
        [TCA_FQ_CODEL_DROP_BATCH_SIZE] = { .type = NLA_U32 },
+       [TCA_FQ_CODEL_MEMORY_LIMIT] = { .type = NLA_U32 },
 };
 
 static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt)
@@ -409,7 +421,11 @@ static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt)
        if (tb[TCA_FQ_CODEL_DROP_BATCH_SIZE])
                q->drop_batch_size = min(1U, nla_get_u32(tb[TCA_FQ_CODEL_DROP_BATCH_SIZE]));
 
-       while (sch->q.qlen > sch->limit) {
+       if (tb[TCA_FQ_CODEL_MEMORY_LIMIT])
+               q->memory_limit = min(1U << 31, nla_get_u32(tb[TCA_FQ_CODEL_MEMORY_LIMIT]));
+
+       while (sch->q.qlen > sch->limit ||
+              q->memory_usage > q->memory_limit) {
                struct sk_buff *skb = fq_codel_dequeue(sch);
 
                q->cstats.drop_len += qdisc_pkt_len(skb);
@@ -454,6 +470,7 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt)
 
        sch->limit = 10*1024;
        q->flows_cnt = 1024;
+       q->memory_limit = 32 << 20; /* 32 MBytes */
        q->drop_batch_size = 64;
        q->quantum = psched_mtu(qdisc_dev(sch));
        q->perturbation = prandom_u32();
@@ -515,6 +532,8 @@ static int fq_codel_dump(struct Qdisc *sch, struct sk_buff *skb)
                        q->quantum) ||
            nla_put_u32(skb, TCA_FQ_CODEL_DROP_BATCH_SIZE,
                        q->drop_batch_size) ||
+           nla_put_u32(skb, TCA_FQ_CODEL_MEMORY_LIMIT,
+                       q->memory_limit) ||
            nla_put_u32(skb, TCA_FQ_CODEL_FLOWS,
                        q->flows_cnt))
                goto nla_put_failure;
@@ -543,6 +562,8 @@ static int fq_codel_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
        st.qdisc_stats.ecn_mark = q->cstats.ecn_mark;
        st.qdisc_stats.new_flow_count = q->new_flow_count;
        st.qdisc_stats.ce_mark = q->cstats.ce_mark;
+       st.qdisc_stats.memory_usage  = q->memory_usage;
+       st.qdisc_stats.drop_overmemory = q->drop_overmemory;
 
        list_for_each(pos, &q->new_flows)
                st.qdisc_stats.new_flows_len++;