????????Memory

????1???????????

????swap in ??si?? == 0??swap out ??so?? == 0

??????ó?????????/????????? <= 70%

????2????????

vmstat
$ vmstat 1
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
0  3 252696   2432    268   7148 3604 2368  3608  2372  288  288  0  0 21 78  1
0  2 253484   2216    228   7104 5368 2976  5372  3036  930  519  0  0  0 100  0
0  1 259252   2616    128   6148 19784 18712 19784 18712 3821 1853  0  1  3 95  1
1  2 260008   2188    144   6824 11824 2584 12664  2584 1347 1174 14  0  0 86  0
2  1 262140   2964    128   5852 24912 17304 24952 17304 4737 2341 86 10  0  0  4

?????????????

????swpd???????? SWAP ????С??KB ???λ??

????free???????????????С??KB ???λ??

????buff??????????????????д??????buffer??С??KB ???λ??

????cache?????????????????????????? cache ??С??KB ???λ??

????si??????? SWAP ????? RAM??swap in?????С??KB ???λ??

????so??????? RAM д?? SWAP??swap out?????С??KB ???λ??

?????????????????????? free ????????????仯??swapd??????????С???????????????? 256MB(????????С) * 10?? = 2.56MB ????????????10???????????????swap??

free
$ free -m
total used free shared buffers cached
Mem: 8111 7185 926 0 243 6299
-/+ buffers/cache: 643 7468
Swap: 8189 0 8189

????????????IO

????1???????????

????iowait % < 20%

????????????????????????????????????????????????????????????????????????

????Linux ?????????????????????ж??????????????????????????????????????ж????????????????????????ж????????????????????????????????????????????????? Linux ????????Щ????????

????2????????

????????????????????????

$ cat /proc/meminfo
MemTotal:      8182776 kB
MemFree:       3053808 kB
Buffers:        342704 kB
Cached:        3972748 kB

?????????????????? 8GB ??????棨MemTotal????3GB ?????????棨MemFree????343MB????????????????棨Buffers????4GB?????????????????????Cached????

sar
$ sar -d 2 3
Linux 2.6.9-42.ELsmp (webserver) 11/30/2008 _i686_ (8 CPU)
11:09:33 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util
11:09:35 PM dev8-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
11:09:35 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util
11:09:37 PM dev8-0 1.00 0.00 12.00 12.00 0.00 0.00 0.00 0.00
11:09:37 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util
11:09:39 PM dev8-0 1.99 0.00 47.76 24.00 0.00 0.50 0.25 0.05
Average: DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util
Average: dev8-0 1.00 0.00 19.97 20.00 0.00 0.33 0.17 0.02

?????????????

????await??????????豸I/O???????????????????λ????

????svctm??????????豸I/O????????????????????λ????

????%util?????????а??????????????I/O??????

???????svctm?????await????????????????I/O???????????????????await????????svctm?????????I/O???е??????????????е???ó?????????

???????%util?????????????????I/O???????I/O???????????????????????????????????

???????Network IO

????????UDP

????1???????????

??????????????????????????е????????????

????2????????

????netstat

????????UDP?????????м?????UDP???????????

$ watch netstat -lunp
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
udp        0      0 0.0.0.0:64000           0.0.0.0:*                           -
udp        0      0 0.0.0.0:38400           0.0.0.0:*                           -
udp        0      0 0.0.0.0:38272           0.0.0.0:*                           -
udp        0      0 0.0.0.0:36992           0.0.0.0:*                           -
udp        0      0 0.0.0.0:17921           0.0.0.0:*                           -
udp        0      0 0.0.0.0:11777           0.0.0.0:*                           -
udp        0      0 0.0.0.0:14721           0.0.0.0:*                           -
udp        0      0 0.0.0.0:36225           0.0.0.0:*                           -

????RecvQ??SendQ?0????????????????????????????

????????UDP???????????????????????????????ò???д???????????????

$ watch netstat -su
Udp:
278073881 packets received
4083356897 packets to unknown port received.
2474435364 packet receive errors
1079038030 packets sent

????packet receive errors ???????????????????????????

?????????ж?“packet receive errors”????????Щ??????????????7?????and?????????checksum??????????????????????????仯???ж?UDP?????????????2??????????????????????????????ж?UDP?????????

"packet receive errors" usually means:
1) data is truncated?? error in checksum while copying
2) udp queue is full?? so it needs to be dropped
3) unable to receive udp package from encapsulated socket
4) sock_queue_rcv_skb() failed with -ENOMEM
5) it is a short packet
6) no space for header in udp packet when validating packet
7) xfrm6_policy_check() fails
many times it means the checksum is not right.