Page daemon frees but doesn't examine?

[Asif]

Hi,

Just a bit curious at the output of vmstat -s.

......
174293 pages paged out
......
0 pages examined by the clock daemon
0 revolutions of the clock hand
174131 pages freed by the clock daemon


Just wondering how the clock daemon pages out pages "without"
examining the them? - Anyone have an explanation?

Thanks,

Asif.

[Darren Dunham]

Asif <asif.sadiq@uk.neceur.com> wrote:

> Hi,

> Just a bit curious at the output of vmstat -s.

What OS?

> .....
> 174293 pages paged out
> .....
> 0 pages examined by the clock daemon
> 0 revolutions of the clock hand
> 174131 pages freed by the clock daemon

> Just wondering how the clock daemon pages out pages "without"
> examining the them? - Anyone have an explanation?

My guess is that this is Solaris 8 or later and that the changes in the
VM handling are not entirely reflected in the vmstat -s messages.

It used to be that all pages were freed by the page scanner, after being
examined and found to be not used recently enough. With large amounts
of memory, this is just too slow, and too time consuming. It limits the
amount of I/O the machine is capable of.

With Solaris 8 and up, the kernel is now capable of freeing memory that
is no longer needed directly, without the page scanner becoming involved
at all.

My suspicion is that the 174131 pages are somehow pages in the past that
would have been freed only through the actions of the page scanner, but
now do not need it. The 'vmstat -s' code is just pulling values from
the kernel, and the text hasn't been rewritten to modify statements that
are no longer strictly true.

It's just a WAG, but I'll bet it's close.

--
Darren Dunham [email]ddunham@taos.com[/email]
Unix System Administrator Taos - The SysAdmin Company
Got some Dr Pepper? San Francisco, CA bay area
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