[PATCH v1 net-next 8/8] selftest: packetdrill: Add test for tcp_collapse().

[Kuniyuki Iwashima <kuniyu@google.com>]

tcp_collapse() now does not collapse high-density skbs and a
low-density skb sandwitched by hihg-density skbs.

tcp_collapse.pkt verifies the behaviour by

1. set a large SO_RCVBUF
2. send one high-density skb with 100 bytes read()
3. send one high-density skb
4. send one low-density skb
5. send one high-density skb
6. send 30 low-density skbs
7. set a small SO_RCVBUF
8. send a small data to trigger tcp_collapse()
9. check TcpExtTCPRcvCollapsed via nstat

Without the series, the first high-density skb is collapsed.
In addition, the first low-density skb drags the following
high-density skb into collapsing, consuming more memory.

If we remove sk_forced_mem_schedule() without this series,
sk->sk_forwad_alloc becomes negative at the end of tcp_collapse().

Note that 30 segments are to make the memory savings large
enough so that the margin can absorb minor size delta of
struct sk_buff or L1_CACHE_BYTES across configs.

skb truesize, TCP_COLLAPSE_MAX_SIZE, TCP_COLLAPSE_SCALING_RATIO
depend on PAGE_SIZE being 4K, so the test is skipped if getconf
returns non-4K PAGE_SIZE.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 .../selftests/net/packetdrill/ksft_runner.sh  |   9 ++
 .../net/packetdrill/tcp_collapse.pkt          | 135 ++++++++++++++++++
 2 files changed, 144 insertions(+)
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_collapse.pkt

diff --git a/tools/testing/selftests/net/packetdrill/ksft_runner.sh b/tools/testing/selftests/net/packetdrill/ksft_runner.sh
index 0a97d5ae3469..250d143bb9f7 100755
--- a/tools/testing/selftests/net/packetdrill/ksft_runner.sh
+++ b/tools/testing/selftests/net/packetdrill/ksft_runner.sh
@@ -44,6 +44,15 @@ if [ -z "$(which packetdrill)" ]; then
 	exit "$KSFT_SKIP"
 fi
 
+page_size=$(grep -E '^--define="?PAGE_SIZE=' $script | sed -E 's/.*PAGE_SIZE="?([0-9]+)"?.*/\1/')
+if [[ -n "$page_size" ]]; then
+	cur_page_size=$(getconf PAGESIZE 2>/dev/null)
+	if [[ "$cur_page_size" != "$page_size" ]]; then
+		ktap_skip_all "requires PAGE_SIZE=$page_size (current: ${cur_page_size:-unknown})"
+		exit "$KSFT_SKIP"
+	fi
+fi
+
 declare -a optargs
 failfunc=ktap_test_fail
 
diff --git a/tools/testing/selftests/net/packetdrill/tcp_collapse.pkt b/tools/testing/selftests/net/packetdrill/tcp_collapse.pkt
new file mode 100644
index 000000000000..90e8be86968f
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_collapse.pkt
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Test that tcp_collapse() only collapses bloated skb runs, skips leading
+// and trailing high-density skbs, skips isolated bloated skbs when collapsing
+// them would not shrink truesize, and properly recovers receive buffer space.
+
+--mss=1000
+--define="PAGE_SIZE=4096"
+
+`./defaults.sh`
+
+// Establish a connection with a large receive buffer.
+// __sock_set_rcvbuf() doubles, so 2000000
+   +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1000000], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 32792 <mss 1000,nop,nop,sackOK,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 65535 <mss 1460,nop,nop,sackOK,nop,wscale 4>
+   +0 < . 1:1(0) ack 1 win 65535
+
+   +0 accept(3, ..., ...) = 4
+
+// 1. Queue two high-density 62,000 B segments (each adds 15 pages of frag
+// truesize with enough margin across NET_SKB_PAD, L1_CACHE_BYTES, and
+// MAX_SKB_FRAGS configs).
+// Read 100 bytes from the first one so before(skb->seq, tp->copied_seq) is true.
+   +0 < P. 1:62001(62000) ack 1 win 65535
+    * > .  1:1(0) ack 62001
+   +0 read(4, ..., 100) = 100
+
+   +0 < P. 62001:124001(62000) ack 1 win 65535
+    * > .  1:1(0) ack 124001
+
+// 2. Queue an isolated bloated 1,000 B segment.
+   +0 < P. 124001:125001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 125001
+
+// 3. Queue another high-density 62,000 B segment.
+   +0 < P. 125001:187001(62000) ack 1 win 65535
+    * > .  1:1(0) ack 187001
+
+// 4. Queue a run of 30 bloated 1,000 B segments.
+   +0 < P. 187001:188001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 188001
+   +0 < P. 188001:189001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 189001
+   +0 < P. 189001:190001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 190001
+   +0 < P. 190001:191001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 191001
+   +0 < P. 191001:192001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 192001
+   +0 < P. 192001:193001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 193001
+   +0 < P. 193001:194001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 194001
+   +0 < P. 194001:195001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 195001
+   +0 < P. 195001:196001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 196001
+   +0 < P. 196001:197001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 197001
+   +0 < P. 197001:198001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 198001
+   +0 < P. 198001:199001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 199001
+   +0 < P. 199001:200001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 200001
+   +0 < P. 200001:201001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 201001
+   +0 < P. 201001:202001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 202001
+   +0 < P. 202001:203001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 203001
+   +0 < P. 203001:204001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 204001
+   +0 < P. 204001:205001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 205001
+   +0 < P. 205001:206001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 206001
+   +0 < P. 206001:207001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 207001
+   +0 < P. 207001:208001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 208001
+   +0 < P. 208001:209001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 209001
+   +0 < P. 209001:210001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 210001
+   +0 < P. 210001:211001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 211001
+   +0 < P. 211001:212001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 212001
+   +0 < P. 212001:213001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 213001
+   +0 < P. 213001:214001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 214001
+   +0 < P. 214001:215001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 215001
+   +0 < P. 215001:216001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 216001
+   +0 < P. 216001:217001(1000) ack 1 win 65535
+    * > .  1:1(0) ack 217001
+
+// 5. Queue a trailing high-density 62,000 B segment.
+   +0 < P. 217001:279001(62000) ack 1 win 65535
+    * > .  1:1(0) ack 279001
+
+// Reset SNMP counters.
+   +0 `nstat -n`
+
+// Shrink SO_RCVBUF so sk_rcvbuf (320,000) is smaller than current
+// sk_rmem_alloc (334,592 on x86_64 default), but larger than sk_rmem_alloc
+// after collapsing the 30 bloated skbs (300,288 on x86_64 default).
+   +0 setsockopt(4, SOL_SOCKET, SO_RCVBUF, [160000], 4) = 0
+
+// Inject the next 1,000 B segment with a changed window to bypass
+// header prediction.  This triggers tcp_prune_queue() -> tcp_collapse().
+// Only the 30 bloated segments should be collapsed; the high-density
+// segments and the isolated bloated segment are skipped.  sk_rmem_alloc
+// shrinks below sk_rcvbuf, so tcp_can_ingest() succeeds and the packet
+// is accepted.
+   +0 < P. 279001:280001(1000) ack 1 win 65534
+    * > .  1:1(0) ack 280001
+
+// Verify exactly 30 skbs were collapsed.
+   +0 `nstat -s | grep TcpExtTCPRcvCollapsed | grep -q " 30 "`
+
+// Verify no packets were dropped.
+   +0 `test -z "$(nstat -s | grep TcpExtTCPRcvQDrop)"`
+
+// Read all remaining queued data to verify data integrity.
+   +0 read(4, ..., 300000) = 279900
-- 
2.56.0.611.g1030f0b940-goog