Re: hard-coded limit on unresolved multicast route cache in ipv4/ipmr.c causes slow, unreliable creation of multicast routes on busy networks
From: Hangbin Liu
Date: Tue Dec 04 2018 - 01:51:18 EST
On Mon, Nov 26, 2018 at 10:44:49AM +0530, Sukumar Gopalakrishnan wrote:
> Hi,
>
> There is a patch to make this queue len configurable. Is below mentioned going
> to be applied ?
>
> http://lkml.iu.edu/hypermail/linux/kernel/1810.3/02344.html
It looks this topic stuckd again..
>
> Regards,
> Sukumar
>
> On Tue, Nov 20, 2018 at 2:55 PM Hangbin Liu <liuhangbin@xxxxxxxxx> wrote:
>
> Hi David,
>
> On Sat, Jul 21, 2018 at 10:03:09PM -0700, David Miller wrote:
> > Yeah that limit is bogus for several reasons.
> ...
> >
> > Therefore, it probably is safe and correct to remove this
> > cache_resolve_queue_len altogether.
> >
> > Something like this:
> >
> > diff --git a/include/linux/mroute_base.h b/include/linux/mroute_base.h
> > index d633f737b3c6..b166465d7c05 100644
> > --- a/include/linux/mroute_base.h
> > +++ b/include/linux/mroute_base.h
> > @@ -234,7 +234,6 @@ struct mr_table_ops {
> > * @mfc_hash: Hash table of all resolved routes for easy lookup
> > * @mfc_cache_list: list of resovled routes for possible traversal
> > * @maxvif: Identifier of highest value vif currently in use
> > - * @cache_resolve_queue_len: current size of unresolved queue
> > * @mroute_do_assert: Whether to inform userspace on wrong ingress
> > * @mroute_do_pim: Whether to receive IGMP PIMv1
> > * @mroute_reg_vif_num: PIM-device vif index
> > @@ -251,7 +250,6 @@ struct mr_table {
> > struct rhltable mfc_hash;
> > struct list_head mfc_cache_list;
> > int maxvif;
> > - atomic_t cache_resolve_queue_len;
> > bool mroute_do_assert;
> > bool mroute_do_pim;
> > int mroute_reg_vif_num;
> > diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
> > index 9f79b9803a16..c007cf9bfe82 100644
> > --- a/net/ipv4/ipmr.c
> > +++ b/net/ipv4/ipmr.c
> > @@ -747,8 +747,6 @@ static void ipmr_destroy_unres(struct mr_table *mrt,
> struct mfc_cache *c)
> > struct sk_buff *skb;
> > struct nlmsgerr *e;
> >
> > - atomic_dec(&mrt->cache_resolve_queue_len);
> > -
> > while ((skb = skb_dequeue(&c->_c.mfc_un.unres.unresolved))) {
> > if (ip_hdr(skb)->version == 0) {
> > struct nlmsghdr *nlh = skb_pull(skb,
> > @@ -1135,9 +1133,11 @@ static int ipmr_cache_unresolved(struct mr_table
> *mrt, vifi_t vifi,
> > }
> >
> > if (!found) {
> > + bool was_empty;
> > +
> > /* Create a new entry if allowable */
> > - if (atomic_read(&mrt->cache_resolve_queue_len) >= 10 ||
> > - (c = ipmr_cache_alloc_unres()) == NULL) {
> > + c = ipmr_cache_alloc_unres();
> > + if (!c) {
> > spin_unlock_bh(&mfc_unres_lock);
> >
> > kfree_skb(skb);
> > @@ -1163,11 +1163,11 @@ static int ipmr_cache_unresolved(struct mr_table
> *mrt, vifi_t vifi,
> > return err;
> > }
> >
> > - atomic_inc(&mrt->cache_resolve_queue_len);
> > + was_empty = list_empty(&mrt->mfc_unres_queue);
> > list_add(&c->_c.list, &mrt->mfc_unres_queue);
> > mroute_netlink_event(mrt, c, RTM_NEWROUTE);
> >
> > - if (atomic_read(&mrt->cache_resolve_queue_len) == 1)
> > + if (was_empty)
> > mod_timer(&mrt->ipmr_expire_timer,
> > c->_c.mfc_un.unres.expires);
>
> In ipmr_expire_process() and ipmr_do_expire_process(), they start mod_timer
> when !list_empty(&mrt->mfc_unres_queue), should here also be !was_empty?
>
> BTW, do you have any plan to apply this patch in kernel?
>
> Regards
> Hangbin
>
> > }
> > @@ -1274,7 +1274,6 @@ static int ipmr_mfc_add(struct net *net, struct
> mr_table *mrt,
> > if (uc->mfc_origin == c->mfc_origin &&
> > uc->mfc_mcastgrp == c->mfc_mcastgrp) {
> > list_del(&_uc->list);
> > - atomic_dec(&mrt->cache_resolve_queue_len);
> > found = true;
> > break;
> > }
> > @@ -1322,7 +1321,7 @@ static void mroute_clean_tables(struct mr_table
> *mrt, bool all)
> > mr_cache_put(c);
> > }
> >
> > - if (atomic_read(&mrt->cache_resolve_queue_len) != 0) {
> > + if (!list_empty(&mrt->mfc_unres_queue)) {
> > spin_lock_bh(&mfc_unres_lock);
> > list_for_each_entry_safe(c, tmp, &mrt->mfc_unres_queue,
> list) {
> > list_del(&c->list);
> > @@ -2648,9 +2647,19 @@ static int ipmr_rtm_route(struct sk_buff *skb,
> struct nlmsghdr *nlh,
> > return ipmr_mfc_delete(tbl, &mfcc, parent);
> > }
> >
> > +static int queue_count(struct mr_table *mrt)
> > +{
> > + struct list_head *pos;
> > + int count = 0;
> > +
> > + list_for_each(pos, &mrt->mfc_unres_queue)
> > + count++;
> > + return count;
> > +}
> > +
> > static bool ipmr_fill_table(struct mr_table *mrt, struct sk_buff *skb)
> > {
> > - u32 queue_len = atomic_read(&mrt->cache_resolve_queue_len);
> > + u32 queue_len = queue_count(mrt);
> >
> > if (nla_put_u32(skb, IPMRA_TABLE_ID, mrt->id) ||
> > nla_put_u32(skb, IPMRA_TABLE_CACHE_RES_QUEUE_LEN, queue_len) ||
> > diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
> > index 0d0f0053bb11..75e9c5a3e7ea 100644
> > --- a/net/ipv6/ip6mr.c
> > +++ b/net/ipv6/ip6mr.c
> > @@ -759,8 +759,6 @@ static void ip6mr_destroy_unres(struct mr_table *mrt,
> struct mfc6_cache *c)
> > struct net *net = read_pnet(&mrt->net);
> > struct sk_buff *skb;
> >
> > - atomic_dec(&mrt->cache_resolve_queue_len);
> > -
> > while ((skb = skb_dequeue(&c->_c.mfc_un.unres.unresolved)) != NULL)
> {
> > if (ipv6_hdr(skb)->version == 0) {
> > struct nlmsghdr *nlh = skb_pull(skb,
> > @@ -1139,8 +1137,8 @@ static int ip6mr_cache_unresolved(struct mr_table
> *mrt, mifi_t mifi,
> > * Create a new entry if allowable
> > */
> >
> > - if (atomic_read(&mrt->cache_resolve_queue_len) >= 10 ||
> > - (c = ip6mr_cache_alloc_unres()) == NULL) {
> > + c = ip6mr_cache_alloc_unres();
> > + if (!c) {
> > spin_unlock_bh(&mfc_unres_lock);
> >
> > kfree_skb(skb);
> > @@ -1167,7 +1165,6 @@ static int ip6mr_cache_unresolved(struct mr_table
> *mrt, mifi_t mifi,
> > return err;
> > }
> >
> > - atomic_inc(&mrt->cache_resolve_queue_len);
> > list_add(&c->_c.list, &mrt->mfc_unres_queue);
> > mr6_netlink_event(mrt, c, RTM_NEWROUTE);
> >
> > @@ -1455,7 +1452,6 @@ static int ip6mr_mfc_add(struct net *net, struct
> mr_table *mrt,
> > if (ipv6_addr_equal(&uc->mf6c_origin, &c->mf6c_origin) &&
> > ipv6_addr_equal(&uc->mf6c_mcastgrp, &c->mf6c_mcastgrp))
> {
> > list_del(&_uc->list);
> > - atomic_dec(&mrt->cache_resolve_queue_len);
> > found = true;
> > break;
> > }
> > @@ -1502,7 +1498,7 @@ static void mroute_clean_tables(struct mr_table
> *mrt, bool all)
> > mr_cache_put(c);
> > }
> >
> > - if (atomic_read(&mrt->cache_resolve_queue_len) != 0) {
> > + if (!list_empty(&mrt->mfc_unres_queue)) {
> > spin_lock_bh(&mfc_unres_lock);
> > list_for_each_entry_safe(c, tmp, &mrt->mfc_unres_queue,
> list) {
> > list_del(&c->list);
>