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fq_codel: add memory limitation per queue
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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>
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Eric Dumazet authored and David S. Miller committed May 9, 2016
1 parent bdabad3 commit 95b5843
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Showing 2 changed files with 27 additions and 3 deletions.
3 changes: 3 additions & 0 deletions include/uapi/linux/pkt_sched.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
};

Expand All @@ -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 {
Expand Down
27 changes: 24 additions & 3 deletions net/sched/sch_fq_codel.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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
Expand All @@ -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;
Expand All @@ -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) {
Expand All @@ -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;
Expand All @@ -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);
Expand Down Expand Up @@ -308,6 +318,7 @@ static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
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,
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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();
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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++;
Expand Down

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