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Thread: Xen memory usage?
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06-16-2011, 10:12 PM #1Junior Guru
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Xen memory usage?
Hi Guys,
I've a 192MB Xen, and from day one (after activation), the memory usage was hovering around 170 - 180MB - even though there's nothing running on it.
But the server is responsive enough (I had a go at compiling some stuff - memory usage level appears to be the same).
But I'm curious to find out why so I submitted a ticket and received a reply that a level3 tech person will look into later.
When I logged in a few minutes ago to check (top -i) - memory usage has dropped to around 59MB.
Code:Tasks: 45 total, 2 running, 43 sleeping, 0 stopped, 0 zombie Cpu(s): 0.0%us, 0.0%sy, 0.0%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.3%st Mem: 196608k total, 59840k used, 136768k free, 7572k buffers Swap: 196600k total, 48k used, 196552k free, 13104k cached
Code:USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.3 2160 716 ? Ss Jun15 0:00 init [3] root 2 0.0 0.0 0 0 ? S< Jun15 0:00 [migration/0] root 3 0.0 0.0 0 0 ? SN Jun15 0:00 [ksoftirqd/0] root 4 0.0 0.0 0 0 ? S< Jun15 0:00 [watchdog/0] root 5 0.0 0.0 0 0 ? S< Jun15 0:00 [events/0] root 6 0.0 0.0 0 0 ? S< Jun15 0:00 [khelper] root 7 0.0 0.0 0 0 ? S< Jun15 0:00 [kthread] root 9 0.0 0.0 0 0 ? S< Jun15 0:00 [xenwatch] root 10 0.0 0.0 0 0 ? S< Jun15 0:00 [xenbus] root 17 0.0 0.0 0 0 ? S< Jun15 0:00 [kblockd/0] root 18 0.0 0.0 0 0 ? S< Jun15 0:00 [cqueue/0] root 22 0.0 0.0 0 0 ? S< Jun15 0:00 [khubd] root 24 0.0 0.0 0 0 ? S< Jun15 0:00 [kseriod] root 84 0.0 0.0 0 0 ? S Jun15 0:00 [khungtaskd] root 87 0.0 0.0 0 0 ? S< Jun15 0:00 [kswapd0] root 88 0.0 0.0 0 0 ? S< Jun15 0:00 [aio/0] root 218 0.0 0.0 0 0 ? S< Jun15 0:00 [kpsmoused] root 243 0.0 0.0 0 0 ? S< Jun15 0:00 [kstriped] root 254 0.0 0.0 0 0 ? S< Jun15 0:00 [kjournald] root 306 0.0 0.3 2356 612 ? S<s Jun15 0:00 /sbin/udevd -d root 607 0.0 0.0 0 0 ? S< Jun15 0:00 [kmpathd/0] root 608 0.0 0.0 0 0 ? S< Jun15 0:00 [kmpath_handlerd] root 689 0.0 0.0 0 0 ? S< Jun15 0:00 [iscsi_eh] root 736 0.0 0.0 0 0 ? S< Jun15 0:00 [ib_addr] root 743 0.0 0.0 0 0 ? S< Jun15 0:00 [ib_mcast] root 744 0.0 0.0 0 0 ? S< Jun15 0:00 [ib_inform] root 745 0.0 0.0 0 0 ? S< Jun15 0:00 [local_sa] root 748 0.0 0.0 0 0 ? S< Jun15 0:00 [iw_cm_wq] root 751 0.0 0.0 0 0 ? S< Jun15 0:00 [ib_cm/0] root 754 0.0 0.0 0 0 ? S< Jun15 0:00 [rdma_cm] root 769 0.0 0.2 22452 548 ? Ssl Jun15 0:00 brcm_iscsiuio root 774 0.0 0.2 3696 536 ? Ss Jun15 0:00 iscsid root 775 0.0 2.1 4152 4148 ? S<Ls Jun15 0:00 iscsid root 977 0.0 0.3 1816 620 ? Ss Jun15 0:00 syslogd -m 0 root 980 0.0 0.2 1764 408 ? Ss Jun15 0:00 klogd -x root 999 0.0 0.5 7204 1036 ? Ss Jun15 0:00 /usr/sbin/sshd root 1007 0.0 0.5 3332 1116 ? Ss Jun15 0:00 crond root 1112 0.0 0.5 2552 1172 ? Ss Jun15 0:00 /bin/sh root 1114 0.0 0.0 0 0 ? S< Jun15 0:00 [kauditd] root 1609 0.0 0.0 0 0 ? S 11:34 0:00 [pdflush] root 1610 0.0 0.0 0 0 ? S 11:34 0:00 [pdflush] root 1636 0.0 1.4 10056 2892 ? Ss 21:39 0:00 sshd: vpswing [priv] vpswing 1638 0.0 0.8 10056 1636 ? S 21:39 0:00 sshd: vpswing@pts/0 vpswing 1639 0.0 0.6 2552 1332 pts/0 Ss 21:39 0:00 -bash vpswing 1656 0.0 0.4 2272 824 pts/0 R+ 21:49 0:00 ps aux
Code:results from high mem. usage 15,16d14 < root,85,0.0,0.0,0,0,?,S,Jun15,0:00,[pdflush] < root,86,0.0,0.0,0,0,?,S,Jun15,0:00,[pdflush] 42,47c40,45 < root,1556,0.0,1.4,10056,2888,?,Ss,10:44,0:00,sshd:,vpswing,[priv] < vpswing,1558,0.0,0.8,10212,1660,?,S,10:44,0:00,sshd:,vpswing@pts/0 < vpswing,1559,0.0,0.6,2552,1356,pts/0,Ss,10:44,0:00,-bash < root,1576,0.0,0.6,2940,1216,pts/0,S,10:49,0:00,su < root,1577,0.0,0.6,2660,1312,pts/0,S,10:49,0:00,bash < root,1603,0.0,0.4,2272,824,pts/0,R+,11:18,0:00,ps,aux --- results from low mem. usage: > root,1609,0.0,0.0,0,0,?,S,11:34,0:00,[pdflush] > root,1610,0.0,0.0,0,0,?,S,11:34,0:00,[pdflush] > root,1636,0.0,1.4,10056,2892,?,Ss,21:39,0:00,sshd:,vpswing,[priv] > vpswing,1638,0.0,0.8,10056,1636,?,S,21:39,0:00,sshd:,vpswing@pts/0 > vpswing,1639,0.0,0.6,2552,1332,pts/0,Ss,21:39,0:00,-bash > vpswing,1656,0.0,0.4,2272,824,pts/0,R+,21:49,0:00,ps,aux
Any clues as to what is happening here?
Many thanks!
Adrian
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06-16-2011, 10:14 PM #2Web Hosting Master
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http://www.linuxatemyram.com/
It's simply caching.
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06-16-2011, 10:16 PM #3Web Hosting Master
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I think it's just that Xens tend to use a lot of memory from the get-go. I'm not sure though; you might want to check up on that .
My personal blog -- rubiverse.net
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06-16-2011, 10:26 PM #4Web Hosting Guru
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06-16-2011, 10:39 PM #5Junior Guru
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Wow ... ok, thanks for that! A relief to hear :-)
But why does it stopped using "disk-caching" now?
free -m shows:
Code:total used free shared buffers cached Mem: 192 59 132 0 8 12 -/+ buffers/cache: 38 153 Swap: 191 0 191
On another note, I have another OpenVZ (also 192MB RAM), and from day 1, it shows:
Code:total used free shared buffers cached Mem: 192 11 180 0 0 0 -/+ buffers/cache: 11 180 Swap: 0 0 0
And, does disk-caching makes the VPS faster?
Many thanks!
Adrian
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06-16-2011, 10:39 PM #6Web Hosting Master
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06-16-2011, 10:49 PM #7Web Hosting Master
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I'm not positive how linux caches the disk, but I do know when my Xen VPS actually uses more memory, some of the memory that's used for disk caching is freed up, but as the system sits idle, the amount of memory disk caching uses comes back.
OpenVZ VPSes don't show memory used for disk caching, however, the VPS node as a whole still caches the disk. It's a part of linux.
Xen behaves more like a dedicated server, hence why you're seeing disk caching. This isn't to say that Xen is faster than OpenVZ because of disk caching. Caching still happens, you just don't see it within an individual OpenVZ VPS.
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06-16-2011, 10:54 PM #8Web Hosting Master
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Unused RAM is wasted RAM .
Linux is nice enough to take care of that for you.~ @PreetamJinka
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06-16-2011, 11:00 PM #9Junior Guru
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06-16-2011, 11:05 PM #10Web Hosting Master
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No problem.
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06-17-2011, 07:22 AM #11Web Hosting Master
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That's assuming the host node has memory available for caching. On a crowded OpenVZ node there could be very little memory available....
With Xen you know exactly how much memory is being used for cache. With OpenVZ you can only hope that some of your stuff is being cached.
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06-17-2011, 12:00 PM #12Junior Guru
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Hi Sleddog,
With Xen you know exactly how much memory is being used for cache. With OpenVZ you can only hope that some of your stuff is being cached.
But why do some folks say all things being equal (e.g. high powered server, not oversold), OpenVZ outperforms Xen?
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06-17-2011, 02:40 PM #13Web Hosting Master
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