Memory Utilisation In Linux, Part 2
#! /usr/bin/python
import time
a=[]
while 1:
a.append('a'*10*1024*1024)
time.sleep(1)
While the above script is running in the background, here is the output from sar -r 5 100:
#sar -r 5 100 Linux 2.6.18-8.1.8.el5 (chihung) 09/09/2008 07:14:29 PM kbmemfree kbmemused %memused kbbuffers kbcached kbswpfree kbswpused %swpused kbswpcad 07:14:34 PM 56396 2019244 97.28 128784 1545336 2031524 84 0.00 0 07:14:39 PM 54876 2020764 97.36 128608 1495564 2031524 84 0.00 0 07:14:44 PM 54704 2020936 97.36 127972 1445768 2031524 84 0.00 0 07:14:49 PM 55540 2020100 97.32 127496 1394408 2031524 84 0.00 0 07:14:54 PM 55600 2020040 97.32 126932 1343752 2031524 84 0.00 0 07:14:59 PM 54452 2021188 97.38 126624 1294228 2031524 84 0.00 0 07:15:04 PM 53116 2022524 97.44 126304 1245076 2031524 84 0.00 0 07:15:09 PM 54484 2021156 97.38 125884 1193316 2031524 84 0.00 0 07:15:09 PM kbmemfree kbmemused %memused kbbuffers kbcached kbswpfree kbswpused %swpused kbswpcad 07:15:14 PM 52784 2022856 97.46 125300 1144816 2031524 84 0.00 0 07:15:19 PM 54800 2020840 97.36 124684 1092436 2031524 84 0.00 0 07:15:24 PM 54920 2020720 97.35 124200 1052136 2031524 84 0.00 0 07:15:29 PM 51652 2023988 97.51 123724 1004592 2031524 84 0.00 0 07:15:34 PM 52280 2023360 97.48 123368 964236 2031524 84 0.00 0 07:15:39 PM 54624 2021016 97.37 122944 912644 2031524 84 0.00 0 07:15:44 PM 53756 2021884 97.41 122576 874024 2031524 84 0.00 0 07:15:44 PM kbmemfree kbmemused %memused kbbuffers kbcached kbswpfree kbswpused %swpused kbswpcad 07:15:49 PM 52632 2023008 97.46 122440 825380 2031524 84 0.00 0 07:15:54 PM 53488 2022152 97.42 122288 775016 2031524 84 0.00 0 07:15:59 PM 52632 2023008 97.46 122068 727192 2031524 84 0.00 0 07:16:04 PM 53220 2022420 97.44 121928 678084 2031524 84 0.00 0 07:16:09 PM 54432 2021208 97.38 121792 627572 2031524 84 0.00 0 07:16:14 PM 52196 2023444 97.49 121436 581396 2031524 84 0.00 0 07:16:19 PM 53572 2022068 97.42 121068 531860 2031524 84 0.00 0 07:16:19 PM kbmemfree kbmemused %memused kbbuffers kbcached kbswpfree kbswpused %swpused kbswpcad 07:16:24 PM 52192 2023448 97.49 120800 485084 2031524 84 0.00 0 07:16:29 PM 51588 2024052 97.51 109316 448756 2031524 84 0.00 0 07:16:34 PM 52528 2023112 97.47 103308 414500 2031524 84 0.00 0 07:16:39 PM 55024 2020616 97.35 96268 369416 2031524 84 0.00 0 07:16:44 PM 54404 2021236 97.38 87060 330008 2031524 84 0.00 0 07:16:49 PM 51752 2023888 97.51 79648 290004 2031524 84 0.00 0 07:16:54 PM 53224 2022416 97.44 68392 250512 2031524 84 0.00 0 07:16:59 PM 54384 2021256 97.38 59184 208384 2031524 84 0.00 0 07:16:59 PM kbmemfree kbmemused %memused kbbuffers kbcached kbswpfree kbswpused %swpused kbswpcad 07:17:04 PM 55544 2020096 97.32 46008 171400 2031524 84 0.00 0 07:17:09 PM 54532 2021108 97.37 28476 141884 2031396 212 0.01 12807:17:14 PM 54372 2021268 97.38 12612 120860 2030756 852 0.04 128 07:17:19 PM 52628 2023012 97.46 2252 85396 2030116 1492 0.07 128 07:17:24 PM 51716 2023924 97.51 144 43988 2009848 21760 1.07 16244 07:17:29 PM 60688 2014952 97.08 208 44044 1956132 75476 3.72 14236 07:17:34 PM 54932 2020708 97.35 216 44068 1915068 116540 5.74 12644 07:17:34 PM kbmemfree kbmemused %memused kbbuffers kbcached kbswpfree kbswpused %swpused kbswpcad 07:17:39 PM 53980 2021660 97.40 216 44160 1878736 152872 7.52 1340 07:17:44 PM 55072 2020568 97.35 212 44208 1823232 208376 10.26 16704 07:17:49 PM 51976 2023664 97.50 220 44276 1779172 252436 12.43 13948 07:17:54 PM 52052 2023588 97.49 228 44176 1734720 296888 14.61 8260 07:17:59 PM 53116 2022524 97.44 236 44104 1671496 360112 17.73 19380 07:18:04 PM 51824 2023816 97.50 268 44012 1628964 402644 19.82 13436 07:18:09 PM 56040 2019600 97.30 276 44396 1557816 473792 23.32 40076 07:18:09 PM kbmemfree kbmemused %memused kbbuffers kbcached kbswpfree kbswpused %swpused kbswpcad 07:18:14 PM 53260 2022380 97.43 288 44364 1544164 487444 23.99 6492 07:18:19 PM 52592 2023048 97.47 288 42052 1473880 557728 27.45 27956 07:18:24 PM 1878472 197168 9.50 372 40140 1943788 87820 4.32 2520 07:18:29 PM 1878596 197044 9.49 384 40108 1943788 87820 4.32 2520 07:18:34 PM 1878844 196796 9.48 384 40108 1943788 87820 4.32 2520 07:18:39 PM 1878968 196672 9.48 392 40108 1943788 87820 4.32 2520 07:18:44 PM 1878968 196672 9.48 396 40168 1943788 87820 4.32 2520 07:18:49 PM 1878968 196672 9.48 404 40184 1943788 87820 4.32 2520
I terminated the Python script at 07:18:24. As you can see, although the %memused started at 97%, it is until 2.5 minutes later we can see swap kicked in. That is about about 1.5GB of memory allocated to the Python program. During this 2.5 minute, the system will page out whatever not necessary in the memory cache to give memory space to the Python program. That's why you do not see any memory shortage or swapping for the first two and a half minutes. However, when the Python program still keep on 'swallowing' more memory, the system has no more memory cache to page out. At this stage, the system has to resolve to swapping out memory pages to swap partition (that's will be in disk). As you can see, the 'kbswpused' and '%swpused' keep going up and this is a clear indication of memory shortage.
When we terminate our Python program, all memory previously allocated in the heap will be returned back to the system. During the entire run of the Python program, it 'swallowed' almost 1.8GB of memory and that's why you will see the %memused dropped down to less than 10%.
posted by chihungchan at 8:04 PM
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