topic Re: bufpages in Operating System - HP-UX

bufpages

Vacquier — Fri, 09 Jan 2004 04:28:58 GMT

Hello,
On HPUX 11, via the command "echo xxxx/D | adb64 -k /stand/vmunix /dev/mem", where xxxx can be phys_mem_pages,maxmem,bufpages and freemem, we can have statistics concerning memory. On some machines, the total of freemem + bufpages may be quite greater than maxmem. Suppose I call kernel_mem the difference between phys_mem_pages and smaxmem. My question is : what does exactly contains these different values, are they distinct or, for example, bufpages may be part of freemem and kernel_mem ?
Thanks in advance for answers.

Re: bufpages

G. Vrijhoeven — Fri, 09 Jan 2004 05:03:24 GMT

Hi,

You have a kernel parameter called pseudo swap on HP-UX 11.00. If that parameter is turned on there can be a difference between the available swap and real swap. The kernel emulated extra pages to use more memory.

You can look into it.

Gideon

Re: bufpages

Vacquier — Mon, 19 Jan 2004 03:46:34 GMT

Hi and thanks fore response.
Does this mean that the values of freemem or bufpages read from the kernel contains part of the pseudo swap area and that's why the total is greater than maxmem ? Actually, I considere that what, in maxmem, is not fremem and bufpages is user memory. In the case of this machine, user memory becomes negative! So have you any idea of how I can find user memory using these kernel values (or others).
Thanks
Serge

Re: bufpages

Dietmar Konermann — Mon, 19 Jan 2004 12:05:01 GMT

Vacquier,

I think you are comparing apples and oranges. :-) The vaiables phys_mem_pages and maxmem contains static information, initialized at boot time, while bufpages and freemem keep changing.

Lets try to explain...

phys_mem_pages
Total number of pages. Discovered at boot time. This is the amount of memory pages the kernel can physically use. Dosn't change.

freemem
Number of pages that are free/unused currently. Changing.

bufpages
Number of pages that are currently in use as Buffer Cache (BC). Changing.

maxmem
At boot time the kernel calculates maxmem by subtracting the minimum BC size in pages (derived from dbc_min_pct if BC size is dynamic) from the current freemem. This is freemem at boot time, so I doubt this metric could be useful later.

To get a quite nice overview how memory is currenly used, you may have a look at the output of crashconf. Note that this does not match e.g. freemem by 100%.

Best regards...
Dietmar.