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Date: Fri, 8 May 2020 11:06:16 -0700 From: Eric Dumazet <edumazet@...gle.com> To: Brian Vazquez <brianvv.kernel@...il.com> Cc: "David S . Miller" <davem@...emloft.net>, netdev <netdev@...r.kernel.org>, Eric Dumazet <eric.dumazet@...il.com> Subject: Re: [PATCH net-next] net/dst: use a smaller percpu_counter batch for dst entries accounting On Fri, May 8, 2020 at 10:30 AM Brian Vazquez <brianvv.kernel@...il.com> wrote: > > On Thu, May 7, 2020 at 7:00 PM Eric Dumazet <edumazet@...gle.com> wrote: > > > > percpu_counter_add() uses a default batch size which is quite big > > on platforms with 256 cpus. (2*256 -> 512) > > > > This means dst_entries_get_fast() can be off by +/- 2*(nr_cpus^2) > > (131072 on servers with 256 cpus) > > > > Reduce the batch size to something more reasonable, and > > add logic to ip6_dst_gc() to call dst_entries_get_slow() > > before calling the _very_ expensive fib6_run_gc() function. > > > > Signed-off-by: Eric Dumazet <edumazet@...gle.com> > > --- > > include/net/dst_ops.h | 4 +++- > > net/core/dst.c | 8 ++++---- > > net/ipv6/route.c | 3 +++ > > 3 files changed, 10 insertions(+), 5 deletions(-) > > > > diff --git a/include/net/dst_ops.h b/include/net/dst_ops.h > > index 443863c7b8da362476c15fd290ac2a32a8aa86e3..88ff7bb2bb9bd950cc54fd5e0ae4573d4c66873d 100644 > > --- a/include/net/dst_ops.h > > +++ b/include/net/dst_ops.h > > @@ -53,9 +53,11 @@ static inline int dst_entries_get_slow(struct dst_ops *dst) > > return percpu_counter_sum_positive(&dst->pcpuc_entries); > > } > > > > +#define DST_PERCPU_COUNTER_BATCH 32 > > static inline void dst_entries_add(struct dst_ops *dst, int val) > > { > > - percpu_counter_add(&dst->pcpuc_entries, val); > > + percpu_counter_add_batch(&dst->pcpuc_entries, val, > > + DST_PERCPU_COUNTER_BATCH); > > } > > > > static inline int dst_entries_init(struct dst_ops *dst) > > diff --git a/net/core/dst.c b/net/core/dst.c > > index 193af526e908afa4b868cf128470f0fbc3850698..d6b6ced0d451a39c0ccb88ae39dba225ea9f5705 100644 > > --- a/net/core/dst.c > > +++ b/net/core/dst.c > > @@ -81,11 +81,11 @@ void *dst_alloc(struct dst_ops *ops, struct net_device *dev, > > { > > struct dst_entry *dst; > > > > - if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) { > > + if (ops->gc && > > + !(flags & DST_NOCOUNT) && > > + dst_entries_get_fast(ops) > ops->gc_thresh) { > > if (ops->gc(ops)) { > > - printk_ratelimited(KERN_NOTICE "Route cache is full: " > > - "consider increasing sysctl " > > - "net.ipv[4|6].route.max_size.\n"); > > + pr_notice_ratelimited("Route cache is full: consider increasing sysctl net.ipv6.route.max_size.\n"); > > return NULL; > > } > > } > > diff --git a/net/ipv6/route.c b/net/ipv6/route.c > > index 1ff142393c768f85c495474a1d05e1ae1642301c..a9072dba00f4fb0b61bce1fc0f44a3a81ba702fa 100644 > > --- a/net/ipv6/route.c > > +++ b/net/ipv6/route.c > > @@ -3195,6 +3195,9 @@ static int ip6_dst_gc(struct dst_ops *ops) > > int entries; > > > > entries = dst_entries_get_fast(ops); > > + if (entries > rt_max_size) > > + entries = dst_entries_get_slow(ops); > > + > > if (time_after(rt_last_gc + rt_min_interval, jiffies) && > if this part of the condition is not satisfied, you are going to call > fib6_run_gc anyways and after that you will update the entries. So I > was wondering if code here could be something like: > --- a/net/ipv6/route.c > +++ b/net/ipv6/route.c > @@ -3197,11 +3197,16 @@ static int ip6_dst_gc(struct dst_ops *ops) > unsigned long rt_last_gc = net->ipv6.ip6_rt_last_gc; > int entries; > > + if (time_before(rt_last_gc + rt_min_interval, jiffies) > + goto run_gc; > + > entries = dst_entries_get_fast(ops); > - if (time_after(rt_last_gc + rt_min_interval, jiffies) && > - entries <= rt_max_size) > + if (entries > rt_max_size) > + entries = dst_entries_get_slow(ops); > + if (entries <= rt_max_size) > goto out; > > +run_gc: > net->ipv6.ip6_rt_gc_expire++; > fib6_run_gc(net->ipv6.ip6_rt_gc_expire, net, true); > entries = dst_entries_get_slow(ops); > > That way you could potentially avoid an extra call to > dst_entries_get_slow when you know for sure that fib6_run_gc will be > run. WDYT? The problem is that you might still return a wrong status in the final : return entries > rt_max_size; If we are in ip6_dst_gc(), we know for sure entries might be wrong, if it holds dst_entries_get_fast(ops) If you prefer, the patch is really (since the caller calls us only if dst_entries_get_fast(ops) was suspect) diff --git a/net/ipv6/route.c b/net/ipv6/route.c index ff847a324220bc4cac8b103640f7e1a5db374a87..78e7f3c14e8a9c937866361aaf641cecfe1fed43 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -3196,7 +3196,7 @@ static int ip6_dst_gc(struct dst_ops *ops) unsigned long rt_last_gc = net->ipv6.ip6_rt_last_gc; int entries; - entries = dst_entries_get_fast(ops); + entries = dst_entries_get_slow(ops); if (time_after(rt_last_gc + rt_min_interval, jiffies) && entries <= rt_max_size) goto out;
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