Pageouts while free memory is avaible

[John Jayaseelan]

Hi,

Attached document is the memory report from glance. Why current & cumulative page out > 0 even though 476MB is free.

Thanks
John Jayaseelan

[Laurent Menase]

It can be memory mapped files

[John Jayaseelan]

I think, If it is mmf file only 'Page Faults' can be increased not pageouts.

[Laurent Menase]

you have page faults when you are trying to access a page not already in memory, - > increment pages in and page faults
you have pages out when the file is written back to the disk.

[Laurent Menase]

If you want to test:
#include
#include
#include

#include

main()
{
char *baseaddr;
int j;
int *current;
int fd;
fd=open("test",O_RDWR|O_CREAT,0666);
ftruncate(fd,31457280);
current=baseaddr=mmap(0,31457280,PROT_READ|PROT_WRITE,MAP_PRIVATE,fd,0);
printf("%x\n",current);
for(j=0;j<31457280;j+=4096)
{
*baseaddr=j;
baseaddr+=4096;
}
}

[Mark Grant]

On HP-ux 11.0 "paged out" can include memory mapped stuff on the vxfs filesystem due to it being a good idea at the time to page to disk.

On 11i, it is memory constraints that cause page outs.

So, is it 11.0?

[John Jayaseelan]

Mark,

The O/S is HP-UX B.11.00. So you mean to say these pageouts is not going to be performance problem.

Thanks

[Joe Short]

In your kernel, is swapmem=1? Some applications do not like psuedo swap, ans behave badly when it is turned on. I have a client that had the same problem, we increased the device swap space, and turned swapmem off, and the problem was resolved.

[Bill Hassell]

Page out rates are the only important metric and single digits are unimportant. Page outs are common with memory mapped files and will occur when there is plenty of unused memory. In your snapshot, page out was 2 for 1Kb, and a high rate of 3 pages...ignore it. Performance will be affected when page out rates are in high double digits (60 and higher) especially if it occurs all the time. The cumulative rate is the most useful as it shows the long term values. Note that page in is not very useful as it combines pages returned from the swap areas as well as pages brought in with each new process, and no way to differentiate between the two rates.

[John Jayaseelan]

Mark,

Is it possible to confirm by any means that the "paged out" are due to memory mapped stuff on the vxfs file system. Are these 'Page out' pages are 'Page in' later or not at all used?

Also swapinfo does not show any increase in the swap usage during these 'Page out'.

Thanks