(sorry for the Double post Bill I hit send too soon)
Bill Anderson wrote:
> Carlos E. R. wrote:
>
> The Thursday 2007-09-20 at 06:41 -0500, David C. Rankin wrote:
>
>
>>>> Ok,
>>>>
>>>> Now I'm confused... After all of the discussion about ram size/swap
>>>> size, I decided to try and make my 1G Toshiba P35 laptop start swapping
>>>> stuff to the swap file.
>>>>
>>>> I opened everything I could think of, 4 konsoles, 2 Open Office
>>>> files,
>>>> 3 Gimps, 2 Firefox, 2 Kongueror, Kjot, knotes, ksnapshot, kstars,
>>>> Amarok, Thunderbird and several more, but the memory required, as shown
>>>> by top, *never* exceeded 1G. The more I would open, the more slight
>>>> slowness would occur, but I *always* had 13k - 15k of memory left and
>>>> *nothing* was ever written to the swap file.
>>>>
>
> It probably was taken from the memory used for buffers. The command
> 'swapon -s' will also tell you the used swap and where.
>
> Just suspend the machine to disk, and get back: you will see that many
> things will remain swaped out. The computer is slow right after waking
> up, because needed things are not in ram and have to be read from
> disk. After a while, it is faster than before because it has got
> ridden himself of useless chunks in memory that has ben swapped out.
>
> -- Cheers,
> Carlos E. R.
>>
> I have been avoiding this thread, because the answer is too long. For
> optimal performance, the kernel pre-allocates buffers and caches. It
> steals from these buffers and caches as it needs memory for
> applications. As for application memory usage, Linux does not keep all
> of the application in memory. Virtual memory is the memory map of an
> application. The physical memory only contains those pages in use by the
> application. Thus, if you run a command like top, you will see the
> virtual size and the resident size. As for swap space, the kernel only
> needs to send the anonymous memory pages of an application to swap
> space, the text (code) can be retrieved from the disk file for the
> application.
> The kernel attempts to keep a certain percentage of memory as free, to
> avoid running out of memory. If a memory shortage occurs, the kernel
> will automatically kill applications based on their oom score. If push
> comes to shove, the kernel shall survive.
> Bill Anderson
> WW7BA
Now that is a great answer! The veil of fog has lifted, I have learned
something new, and I understand a lot better now why my memory
allocation and swap behavior appear as they do in top. Thanks!
--
David C. Rankin, J.D., P.E.
Rankin Law Firm, PLLC
510 Ochiltree Street
Nacogdoches, Texas 75961
(936) 715-9333
(936) 715-9339 fax
www.rankinlawfirm.com
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