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09-01-2009 09:12 AM
09-01-2009 09:12 AM
virtual and swap
I have heard that swap memory and virtual memory both are the same.
But why we use 2 different commands swapinfo and vmstat ?
I know that swap is part of HDD
but when virtual memory comes in to picture..
When idle processes are sent to swap from RAM and vice versa its called as pagein and pageout
But this p0 and pi status shown in vmstat not swapinfo
m really confused..plz help me
regards
himacs
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09-01-2009 09:58 AM
09-01-2009 09:58 AM
Re: virtual and swap
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09-01-2009 10:27 AM
09-01-2009 10:27 AM
Re: virtual and swap
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09-01-2009 11:15 AM
09-01-2009 11:15 AM
Re: virtual and swap
vmstat gives more info on the current performance.
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09-01-2009 11:44 AM
09-01-2009 11:44 AM
Re: virtual and swap
To add to Dennis's comments, remember that every process has to "reserve" swap space so that it is available should the process ever need it (be paged out).
If you don't have sufficient swap space, forking a new process will result in ENOMEM (errno 12).
Whether or not your process ever uses the reservation is dependent upon memory pressure. If pages of a process are paged-out, the actual I/O that occurs is seen in the 'po' column of 'vmstat'. When values in this column begin to reach double-digits, your performance has degraded.
Regards!
...JRF...
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09-01-2009 11:57 AM
09-01-2009 11:57 AM
Re: virtual and swap
Check this out about detailed vmstat:
http://forums13.itrc.hp.com/service/forums/questionanswer.do?admit=109447627+1251834846043+28353475&threadId=1347885
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09-01-2009 07:24 PM
09-01-2009 07:24 PM
Re: virtual and swap
swapinfo â system paging space information. swapinfo prints information about device and file system paging space. (Note: the term `swap' refers to an obsolete implementation of virtual memory; HP-UX actually implements virtual memory by way of paging rather than swapping. This command and others retain names derived from `swap' for historical reasons.) For more details check it:
http://docs.hp.com/en/B2355-60105/swapinfo.1M.html
vmstat-vmstat â report virtual memory statistics. The vmstat command reports certain statistics kept about process, virtual memory, trap, and CPU activity. It also can clear the accumulators in the kernel sum structure. For more details check it:
http://docs.hp.com/en/B2355-60127/vmstat.1.html
Rgds-Kranti