* [PATCH net-next v5] net: ip: avoid OOM kills with large UDP sends over loopback
@ 2021-06-24 17:57 Jakub Kicinski
2021-06-27 8:11 ` Leon Romanovsky
0 siblings, 1 reply; 2+ messages in thread
From: Jakub Kicinski @ 2021-06-24 17:57 UTC (permalink / raw)
To: davem
Cc: netdev, willemb, eric.dumazet, dsahern, yoshfuji, brouer,
Jakub Kicinski, Dave Jones
Dave observed number of machines hitting OOM on the UDP send
path. The workload seems to be sending large UDP packets over
loopback. Since loopback has MTU of 64k kernel will try to
allocate an skb with up to 64k of head space. This has a good
chance of failing under memory pressure. What's worse if
the message length is <32k the allocation may trigger an
OOM killer.
This is entirely avoidable, we can use an skb with page frags.
af_unix solves a similar problem by limiting the head
length to SKB_MAX_ALLOC. This seems like a good and simple
approach. It means that UDP messages > 16kB will now
use fragments if underlying device supports SG, if extra
allocator pressure causes regressions in real workloads
we can switch to trying the large allocation first and
falling back.
v4: pre-calculate all the additions to alloclen so
we can be sure it won't go over order-2
v5: s/< MAX/<= MAX/ ; reorder variable declaration
Reported-by: Dave Jones <dsj@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
net/ipv4/ip_output.c | 32 ++++++++++++++++++--------------
net/ipv6/ip6_output.c | 32 +++++++++++++++++---------------
2 files changed, 35 insertions(+), 29 deletions(-)
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index c3efc7d658f6..f5c398036efa 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1050,11 +1050,11 @@ static int __ip_append_data(struct sock *sk,
if (copy < length)
copy = maxfraglen - skb->len;
if (copy <= 0) {
+ unsigned int alloclen, alloc_extra;
char *data;
unsigned int datalen;
unsigned int fraglen;
unsigned int fraggap;
- unsigned int alloclen;
unsigned int pagedlen;
struct sk_buff *skb_prev;
alloc_new_skb:
@@ -1074,35 +1074,39 @@ static int __ip_append_data(struct sock *sk,
fraglen = datalen + fragheaderlen;
pagedlen = 0;
+ alloc_extra = hh_len + 15;
+ alloc_extra += exthdrlen;
+
+ /* The last fragment gets additional space at tail.
+ * Note, with MSG_MORE we overallocate on fragments,
+ * because we have no idea what fragment will be
+ * the last.
+ */
+ if (datalen == length + fraggap)
+ alloc_extra += rt->dst.trailer_len;
+
if ((flags & MSG_MORE) &&
!(rt->dst.dev->features&NETIF_F_SG))
alloclen = mtu;
- else if (!paged)
+ else if (!paged &&
+ (fraglen + alloc_extra <= SKB_MAX_ALLOC ||
+ !(rt->dst.dev->features & NETIF_F_SG)))
alloclen = fraglen;
else {
alloclen = min_t(int, fraglen, MAX_HEADER);
pagedlen = fraglen - alloclen;
}
- alloclen += exthdrlen;
-
- /* The last fragment gets additional space at tail.
- * Note, with MSG_MORE we overallocate on fragments,
- * because we have no idea what fragment will be
- * the last.
- */
- if (datalen == length + fraggap)
- alloclen += rt->dst.trailer_len;
+ alloclen += alloc_extra;
if (transhdrlen) {
- skb = sock_alloc_send_skb(sk,
- alloclen + hh_len + 15,
+ skb = sock_alloc_send_skb(sk, alloclen,
(flags & MSG_DONTWAIT), &err);
} else {
skb = NULL;
if (refcount_read(&sk->sk_wmem_alloc) + wmem_alloc_delta <=
2 * sk->sk_sndbuf)
- skb = alloc_skb(alloclen + hh_len + 15,
+ skb = alloc_skb(alloclen,
sk->sk_allocation);
if (unlikely(!skb))
err = -ENOBUFS;
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index ff4f9ebcf7f6..afe887dd5e35 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1551,11 +1551,11 @@ static int __ip6_append_data(struct sock *sk,
copy = maxfraglen - skb->len;
if (copy <= 0) {
+ unsigned int alloclen, alloc_extra;
char *data;
unsigned int datalen;
unsigned int fraglen;
unsigned int fraggap;
- unsigned int alloclen;
unsigned int pagedlen;
alloc_new_skb:
/* There's no room in the current skb */
@@ -1582,17 +1582,28 @@ static int __ip6_append_data(struct sock *sk,
fraglen = datalen + fragheaderlen;
pagedlen = 0;
+ alloc_extra = hh_len;
+ alloc_extra += dst_exthdrlen;
+ alloc_extra += rt->dst.trailer_len;
+
+ /* We just reserve space for fragment header.
+ * Note: this may be overallocation if the message
+ * (without MSG_MORE) fits into the MTU.
+ */
+ alloc_extra += sizeof(struct frag_hdr);
+
if ((flags & MSG_MORE) &&
!(rt->dst.dev->features&NETIF_F_SG))
alloclen = mtu;
- else if (!paged)
+ else if (!paged &&
+ (fraglen + alloc_extra <= SKB_MAX_ALLOC ||
+ !(rt->dst.dev->features & NETIF_F_SG)))
alloclen = fraglen;
else {
alloclen = min_t(int, fraglen, MAX_HEADER);
pagedlen = fraglen - alloclen;
}
-
- alloclen += dst_exthdrlen;
+ alloclen += alloc_extra;
if (datalen != length + fraggap) {
/*
@@ -1602,30 +1613,21 @@ static int __ip6_append_data(struct sock *sk,
datalen += rt->dst.trailer_len;
}
- alloclen += rt->dst.trailer_len;
fraglen = datalen + fragheaderlen;
- /*
- * We just reserve space for fragment header.
- * Note: this may be overallocation if the message
- * (without MSG_MORE) fits into the MTU.
- */
- alloclen += sizeof(struct frag_hdr);
-
copy = datalen - transhdrlen - fraggap - pagedlen;
if (copy < 0) {
err = -EINVAL;
goto error;
}
if (transhdrlen) {
- skb = sock_alloc_send_skb(sk,
- alloclen + hh_len,
+ skb = sock_alloc_send_skb(sk, alloclen,
(flags & MSG_DONTWAIT), &err);
} else {
skb = NULL;
if (refcount_read(&sk->sk_wmem_alloc) + wmem_alloc_delta <=
2 * sk->sk_sndbuf)
- skb = alloc_skb(alloclen + hh_len,
+ skb = alloc_skb(alloclen,
sk->sk_allocation);
if (unlikely(!skb))
err = -ENOBUFS;
--
2.31.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH net-next v5] net: ip: avoid OOM kills with large UDP sends over loopback
2021-06-24 17:57 [PATCH net-next v5] net: ip: avoid OOM kills with large UDP sends over loopback Jakub Kicinski
@ 2021-06-27 8:11 ` Leon Romanovsky
0 siblings, 0 replies; 2+ messages in thread
From: Leon Romanovsky @ 2021-06-27 8:11 UTC (permalink / raw)
To: Jakub Kicinski
Cc: davem, netdev, willemb, eric.dumazet, dsahern, yoshfuji, brouer,
Dave Jones
On Thu, Jun 24, 2021 at 10:57:24AM -0700, Jakub Kicinski wrote:
> Dave observed number of machines hitting OOM on the UDP send
> path. The workload seems to be sending large UDP packets over
> loopback. Since loopback has MTU of 64k kernel will try to
> allocate an skb with up to 64k of head space. This has a good
> chance of failing under memory pressure. What's worse if
> the message length is <32k the allocation may trigger an
> OOM killer.
>
> This is entirely avoidable, we can use an skb with page frags.
>
> af_unix solves a similar problem by limiting the head
> length to SKB_MAX_ALLOC. This seems like a good and simple
> approach. It means that UDP messages > 16kB will now
> use fragments if underlying device supports SG, if extra
> allocator pressure causes regressions in real workloads
> we can switch to trying the large allocation first and
> falling back.
>
> v4: pre-calculate all the additions to alloclen so
> we can be sure it won't go over order-2
> v5: s/< MAX/<= MAX/ ; reorder variable declaration
Jakub,
Can you please put changelog under "---" below SOB?
It gives no value to see all vX in the final git log.
Thanks
>
> Reported-by: Dave Jones <dsj@fb.com>
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> net/ipv4/ip_output.c | 32 ++++++++++++++++++--------------
> net/ipv6/ip6_output.c | 32 +++++++++++++++++---------------
> 2 files changed, 35 insertions(+), 29 deletions(-)
>
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index c3efc7d658f6..f5c398036efa 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -1050,11 +1050,11 @@ static int __ip_append_data(struct sock *sk,
> if (copy < length)
> copy = maxfraglen - skb->len;
> if (copy <= 0) {
> + unsigned int alloclen, alloc_extra;
> char *data;
> unsigned int datalen;
> unsigned int fraglen;
> unsigned int fraggap;
> - unsigned int alloclen;
> unsigned int pagedlen;
> struct sk_buff *skb_prev;
> alloc_new_skb:
> @@ -1074,35 +1074,39 @@ static int __ip_append_data(struct sock *sk,
> fraglen = datalen + fragheaderlen;
> pagedlen = 0;
>
> + alloc_extra = hh_len + 15;
> + alloc_extra += exthdrlen;
> +
> + /* The last fragment gets additional space at tail.
> + * Note, with MSG_MORE we overallocate on fragments,
> + * because we have no idea what fragment will be
> + * the last.
> + */
> + if (datalen == length + fraggap)
> + alloc_extra += rt->dst.trailer_len;
> +
> if ((flags & MSG_MORE) &&
> !(rt->dst.dev->features&NETIF_F_SG))
> alloclen = mtu;
> - else if (!paged)
> + else if (!paged &&
> + (fraglen + alloc_extra <= SKB_MAX_ALLOC ||
> + !(rt->dst.dev->features & NETIF_F_SG)))
> alloclen = fraglen;
> else {
> alloclen = min_t(int, fraglen, MAX_HEADER);
> pagedlen = fraglen - alloclen;
> }
>
> - alloclen += exthdrlen;
> -
> - /* The last fragment gets additional space at tail.
> - * Note, with MSG_MORE we overallocate on fragments,
> - * because we have no idea what fragment will be
> - * the last.
> - */
> - if (datalen == length + fraggap)
> - alloclen += rt->dst.trailer_len;
> + alloclen += alloc_extra;
>
> if (transhdrlen) {
> - skb = sock_alloc_send_skb(sk,
> - alloclen + hh_len + 15,
> + skb = sock_alloc_send_skb(sk, alloclen,
> (flags & MSG_DONTWAIT), &err);
> } else {
> skb = NULL;
> if (refcount_read(&sk->sk_wmem_alloc) + wmem_alloc_delta <=
> 2 * sk->sk_sndbuf)
> - skb = alloc_skb(alloclen + hh_len + 15,
> + skb = alloc_skb(alloclen,
> sk->sk_allocation);
> if (unlikely(!skb))
> err = -ENOBUFS;
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index ff4f9ebcf7f6..afe887dd5e35 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1551,11 +1551,11 @@ static int __ip6_append_data(struct sock *sk,
> copy = maxfraglen - skb->len;
>
> if (copy <= 0) {
> + unsigned int alloclen, alloc_extra;
> char *data;
> unsigned int datalen;
> unsigned int fraglen;
> unsigned int fraggap;
> - unsigned int alloclen;
> unsigned int pagedlen;
> alloc_new_skb:
> /* There's no room in the current skb */
> @@ -1582,17 +1582,28 @@ static int __ip6_append_data(struct sock *sk,
> fraglen = datalen + fragheaderlen;
> pagedlen = 0;
>
> + alloc_extra = hh_len;
> + alloc_extra += dst_exthdrlen;
> + alloc_extra += rt->dst.trailer_len;
> +
> + /* We just reserve space for fragment header.
> + * Note: this may be overallocation if the message
> + * (without MSG_MORE) fits into the MTU.
> + */
> + alloc_extra += sizeof(struct frag_hdr);
> +
> if ((flags & MSG_MORE) &&
> !(rt->dst.dev->features&NETIF_F_SG))
> alloclen = mtu;
> - else if (!paged)
> + else if (!paged &&
> + (fraglen + alloc_extra <= SKB_MAX_ALLOC ||
> + !(rt->dst.dev->features & NETIF_F_SG)))
> alloclen = fraglen;
> else {
> alloclen = min_t(int, fraglen, MAX_HEADER);
> pagedlen = fraglen - alloclen;
> }
> -
> - alloclen += dst_exthdrlen;
> + alloclen += alloc_extra;
>
> if (datalen != length + fraggap) {
> /*
> @@ -1602,30 +1613,21 @@ static int __ip6_append_data(struct sock *sk,
> datalen += rt->dst.trailer_len;
> }
>
> - alloclen += rt->dst.trailer_len;
> fraglen = datalen + fragheaderlen;
>
> - /*
> - * We just reserve space for fragment header.
> - * Note: this may be overallocation if the message
> - * (without MSG_MORE) fits into the MTU.
> - */
> - alloclen += sizeof(struct frag_hdr);
> -
> copy = datalen - transhdrlen - fraggap - pagedlen;
> if (copy < 0) {
> err = -EINVAL;
> goto error;
> }
> if (transhdrlen) {
> - skb = sock_alloc_send_skb(sk,
> - alloclen + hh_len,
> + skb = sock_alloc_send_skb(sk, alloclen,
> (flags & MSG_DONTWAIT), &err);
> } else {
> skb = NULL;
> if (refcount_read(&sk->sk_wmem_alloc) + wmem_alloc_delta <=
> 2 * sk->sk_sndbuf)
> - skb = alloc_skb(alloclen + hh_len,
> + skb = alloc_skb(alloclen,
> sk->sk_allocation);
> if (unlikely(!skb))
> err = -ENOBUFS;
> --
> 2.31.1
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2021-06-24 17:57 [PATCH net-next v5] net: ip: avoid OOM kills with large UDP sends over loopback Jakub Kicinski
2021-06-27 8:11 ` Leon Romanovsky
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