From: "Michael S. Tsirkin" <mst@redhat.com>
To: Eric Dumazet <edumazet@google.com>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
Eric Dumazet <eric.dumazet@gmail.com>,
netdev <netdev@vger.kernel.org>,
Alexander Duyck <alexanderduyck@fb.com>,
Paolo Abeni <pabeni@redhat.com>, Greg Thelen <gthelen@google.com>,
"David S . Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
su-lifan@linux.alibaba.com, "dust.li" <dust.li@linux.alibaba.com>,
Jason Wang <jasowang@redhat.com>
Subject: Re: [PATCH net] net: avoid 32 x truesize under-estimation for tiny skbs
Date: Wed, 31 Mar 2021 04:11:12 -0400 [thread overview]
Message-ID: <20210331040405-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CANn89iLXfu7mdk+cxqVYxtJhfBQtpho6i2kyOEUbEGPXBQj+jg@mail.gmail.com>
On Mon, Mar 29, 2021 at 11:06:09AM +0200, Eric Dumazet wrote:
> On Mon, Mar 29, 2021 at 10:52 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> >
> > On Wed, 13 Jan 2021 08:18:19 -0800, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > > From: Eric Dumazet <edumazet@google.com>
> > >
> > > Both virtio net and napi_get_frags() allocate skbs
> > > with a very small skb->head
> > >
> > > While using page fragments instead of a kmalloc backed skb->head might give
> > > a small performance improvement in some cases, there is a huge risk of
> > > under estimating memory usage.
> > >
> > > For both GOOD_COPY_LEN and GRO_MAX_HEAD, we can fit at least 32 allocations
> > > per page (order-3 page in x86), or even 64 on PowerPC
> > >
> > > We have been tracking OOM issues on GKE hosts hitting tcp_mem limits
> > > but consuming far more memory for TCP buffers than instructed in tcp_mem[2]
> > >
> > > Even if we force napi_alloc_skb() to only use order-0 pages, the issue
> > > would still be there on arches with PAGE_SIZE >= 32768
> > >
> > > This patch makes sure that small skb head are kmalloc backed, so that
> > > other objects in the slab page can be reused instead of being held as long
> > > as skbs are sitting in socket queues.
> > >
> > > Note that we might in the future use the sk_buff napi cache,
> > > instead of going through a more expensive __alloc_skb()
> > >
> > > Another idea would be to use separate page sizes depending
> > > on the allocated length (to never have more than 4 frags per page)
> > >
> > > I would like to thank Greg Thelen for his precious help on this matter,
> > > analysing crash dumps is always a time consuming task.
> >
> >
> > This patch causes a performance degradation of about 10% in the scenario of
> > virtio-net + GRO.
> >
> > For GRO, there is no way to merge skbs based on frags with this patch, only
> > frag_list can be used to link skbs. The problem that this cause are that compared
> > to the GRO package merged into the frags way, the current skb needs to call
> > kfree_skb_list to release each skb, resulting in performance degradation.
> >
> > virtio-net will store some data onto the linear space after receiving it. In
> > addition to the header, there are also some payloads, so "headlen <= offset"
> > fails. And skb->head_frag is failing when use kmalloc() for skb->head allocation.
> >
>
> Thanks for the report.
>
> There is no way we can make things both fast for existing strategies
> used by _insert_your_driver
> and malicious usages of data that can sit for seconds/minutes in socket queues.
>
> I think that if you want to gain this 10% back, you have to change
> virtio_net to meet optimal behavior.
>
> Normal drivers make sure to not pull payload in skb->head, only headers.
Hmm we do have hdr_len field, but seem to ignore it on RX.
Jason do you see any issues with using it for the head len?
> Optimal GRO packets are when payload is in page fragments.
>
> (I am speaking not only for raw performance, but ability for systems
> to cope with network outages and sudden increase of memory usage in
> out of order queues)
>
> This has been quite clearly stated in my changelog.
>
> Thanks.
>
>
> > int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
> > {
> > struct skb_shared_info *pinfo, *skbinfo = skb_shinfo(skb);
> > unsigned int offset = skb_gro_offset(skb);
> > unsigned int headlen = skb_headlen(skb);
> >
> > .......
> >
> > if (headlen <= offset) { // virtio-net will fail
> > ........ // merge by frags
> > goto done;
> > } else if (skb->head_frag) { // skb->head_frag is fail when use kmalloc() for skb->head allocation
> > ........ // merge by frags
> > goto done;
> > }
> >
> > merge:
> > ......
> >
> > if (NAPI_GRO_CB(p)->last == p)
> > skb_shinfo(p)->frag_list = skb;
> > else
> > NAPI_GRO_CB(p)->last->next = skb;
> >
> > ......
> > return 0;
> > }
> >
> >
> > test cmd:
> > for i in $(seq 1 4)
> > do
> > redis-benchmark -r 10000000 -n 10000000 -t set -d 1024 -c 8 -P 32 -h <ip> -p 6379 2>&1 | grep 'per second' &
> > done
> >
> > Reported-by: su-lifan@linux.alibaba.com
> >
> > >
> > > Fixes: fd11a83dd363 ("net: Pull out core bits of __netdev_alloc_skb and add __napi_alloc_skb")
> > > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > > Cc: Alexander Duyck <alexanderduyck@fb.com>
> > > Cc: Paolo Abeni <pabeni@redhat.com>
> > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > Cc: Greg Thelen <gthelen@google.com>
> > > ---
> > > net/core/skbuff.c | 9 +++++++--
> > > 1 file changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > > index 7626a33cce590e530f36167bd096026916131897..3a8f55a43e6964344df464a27b9b1faa0eb804f3 100644
> > > --- a/net/core/skbuff.c
> > > +++ b/net/core/skbuff.c
> > > @@ -501,13 +501,17 @@ EXPORT_SYMBOL(__netdev_alloc_skb);
> > > struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
> > > gfp_t gfp_mask)
> > > {
> > > - struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
> > > + struct napi_alloc_cache *nc;
> > > struct sk_buff *skb;
> > > void *data;
> > >
> > > len += NET_SKB_PAD + NET_IP_ALIGN;
> > >
> > > - if ((len > SKB_WITH_OVERHEAD(PAGE_SIZE)) ||
> > > + /* If requested length is either too small or too big,
> > > + * we use kmalloc() for skb->head allocation.
> > > + */
> > > + if (len <= SKB_WITH_OVERHEAD(1024) ||
> > > + len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
> > > (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
> > > skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE);
> > > if (!skb)
> > > @@ -515,6 +519,7 @@ struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
> > > goto skb_success;
> > > }
> > >
> > > + nc = this_cpu_ptr(&napi_alloc_cache);
> > > len += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> > > len = SKB_DATA_ALIGN(len);
> > >
> > > --
> > > 2.30.0.284.gd98b1dd5eaa7-goog
> > >
next prev parent reply other threads:[~2021-03-31 8:12 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-13 16:18 [PATCH net] net: avoid 32 x truesize under-estimation for tiny skbs Eric Dumazet
2021-01-13 18:00 ` Alexander Duyck
2021-01-13 19:19 ` Michael S. Tsirkin
2021-01-13 22:23 ` David Laight
2021-01-14 5:16 ` Eric Dumazet
2021-01-14 9:29 ` David Laight
2021-01-14 19:00 ` patchwork-bot+netdevbpf
[not found] ` <1617007696.5731978-1-xuanzhuo@linux.alibaba.com>
2021-03-29 9:06 ` Eric Dumazet
2021-03-31 8:11 ` Michael S. Tsirkin [this message]
2021-03-31 8:36 ` Eric Dumazet
2021-03-31 8:46 ` Eric Dumazet
2021-03-31 8:49 ` Eric Dumazet
2021-03-31 8:54 ` Eric Dumazet
[not found] ` <1617248264.4993114-2-xuanzhuo@linux.alibaba.com>
2021-04-01 5:06 ` Eric Dumazet
[not found] ` <1617357110.3822439-1-xuanzhuo@linux.alibaba.com>
2021-04-02 12:52 ` Eric Dumazet
2021-04-01 13:51 ` Michael S. Tsirkin
2021-04-01 14:08 ` Eric Dumazet
2021-04-01 7:14 ` Jason Wang
[not found] ` <1617267183.5697193-1-xuanzhuo@linux.alibaba.com>
2021-04-01 9:58 ` Eric Dumazet
2021-04-02 2:52 ` Jason Wang
[not found] ` <1617361253.1788838-2-xuanzhuo@linux.alibaba.com>
2021-04-02 12:53 ` Eric Dumazet
2021-04-06 2:04 ` Jason Wang
[not found] ` <1617190239.1035674-1-xuanzhuo@linux.alibaba.com>
2021-03-31 12:08 ` Eric Dumazet
2021-04-01 13:36 ` Michael S. Tsirkin
2022-09-07 20:19 ` Paolo Abeni
2022-09-07 20:40 ` Eric Dumazet
2022-09-08 10:48 ` Paolo Abeni
2022-09-08 12:20 ` Eric Dumazet
2022-09-08 14:26 ` Paolo Abeni
2022-09-08 16:00 ` Eric Dumazet
2022-09-07 21:36 ` Alexander H Duyck
2022-09-08 11:00 ` Paolo Abeni
2022-09-08 14:53 ` Alexander H Duyck
2022-09-08 18:01 ` Paolo Abeni
2022-09-08 19:26 ` Alexander Duyck
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210331040405-mutt-send-email-mst@kernel.org \
--to=mst@redhat.com \
--cc=alexanderduyck@fb.com \
--cc=davem@davemloft.net \
--cc=dust.li@linux.alibaba.com \
--cc=edumazet@google.com \
--cc=eric.dumazet@gmail.com \
--cc=gthelen@google.com \
--cc=jasowang@redhat.com \
--cc=kuba@kernel.org \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=su-lifan@linux.alibaba.com \
--cc=xuanzhuo@linux.alibaba.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).