[PATCH 1/3] fq.h: Port memory limit mechanism from fq_codel

[Toke Høiland-Jørgensen]

The reusable fairness queueing implementation (fq.h) lacks the memory
usage limit that the fq_codel qdisc has. This means that small
devices (e.g. WiFi routers) can run out of memory when flooded with a
large number of packets. This ports the memory limit feature from
fq_codel to fq.h.

Signed-off-by: Toke Høiland-Jørgensen <t...@toke.dk>
---
 include/net/fq.h      | 3 +++
 include/net/fq_impl.h | 7 ++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/net/fq.h b/include/net/fq.h
index 268b490..6d8521a 100644
--- a/include/net/fq.h
+++ b/include/net/fq.h
@@ -72,9 +72,12 @@ struct fq {
        u32 flows_cnt;
        u32 perturbation;
        u32 limit;
+       u32 memory_limit;
+       u32 memory_usage;
        u32 quantum;
        u32 backlog;
        u32 overlimit;
+       u32 overmemory;
        u32 collisions;
 };
 
diff --git a/include/net/fq_impl.h b/include/net/fq_impl.h
index 163f3ed..4e6131c 100644
--- a/include/net/fq_impl.h
+++ b/include/net/fq_impl.h
@@ -29,6 +29,7 @@ static struct sk_buff *fq_flow_dequeue(struct fq *fq,
        tin->backlog_packets--;
        flow->backlog -= skb->len;
        fq->backlog--;
+       fq->memory_usage -= skb->truesize;
 
        if (flow->backlog == 0) {
                list_del_init(&flow->backlogchain);
@@ -154,6 +155,7 @@ static void fq_tin_enqueue(struct fq *fq,
        flow->backlog += skb->len;
        tin->backlog_bytes += skb->len;
        tin->backlog_packets++;
+       fq->memory_usage += skb->truesize;
        fq->backlog++;
 
        fq_recalc_backlog(fq, tin, flow);
@@ -166,7 +168,7 @@ static void fq_tin_enqueue(struct fq *fq,
 
        __skb_queue_tail(&flow->queue, skb);
 
-       if (fq->backlog > fq->limit) {
+       if (fq->backlog > fq->limit || fq->memory_usage > fq->memory_limit) {
                flow = list_first_entry_or_null(&fq->backlogs,
                                                struct fq_flow,
                                                backlogchain);
@@ -181,6 +183,8 @@ static void fq_tin_enqueue(struct fq *fq,
 
                flow->tin->overlimit++;
                fq->overlimit++;
+               if (fq->memory_usage > fq->memory_limit)
+                       fq->overmemory++;
        }
 }
 
@@ -251,6 +255,7 @@ static int fq_init(struct fq *fq, int flows_cnt)
        fq->perturbation = prandom_u32();
        fq->quantum = 300;
        fq->limit = 8192;
+       fq->memory_limit = 16 << 20; /* 16 MBytes */
 
        fq->flows = kcalloc(fq->flows_cnt, sizeof(fq->flows[0]), GFP_KERNEL);
        if (!fq->flows)
-- 
2.9.3