Re: Kernel cached memory

From: Bill Davidsen
Date: Mon Aug 01 2005 - 16:07:10 EST


Gábor Lénárt wrote:

On Mon, Jul 25, 2005 at 12:47:50PM -0400, Bill Davidsen wrote:


Gábor Lénárt wrote:


On Fri, Jul 22, 2005 at 05:46:58PM +0800, Ashley wrote:



I've a server with 2 Operton 64bit CPU and 12G memory, and this server is used to run applications which will comsume huge memory,
the problem is: when this aplications exits, the free memory of the server is still very low(accroding to the output of "top"), and


from the output of command "free", I can see that many GB memory was


cached by kernel. Does anyone know how to free the kernel cached
memory? thanks in advance.


It's a very - very - very old and bad logic (at least nowdays) from the
stone age to free up memory.


It's very Microsoft to claim that the OS always knows best, and not let the user tune the system the way they want it tuned. And if that means to leave a bunch of free memory for absolute fastest availability, the admin should have that option.



Sure, sorry if my comment can be treated in this way ... I mean surprising
amount of people I've met criticised Linux (well, some years ago when DOS
was popular) that he/she want to see that 'free memory' field reported eg by
'top' should be the maximum all the time ... I mean this way: this is the
behaviour which is quite wrong, I've written about this.

Sure, because of my not too good English, I may have missed the real meaning
of the mail, sorry about it!

Well, I thought I understood "from the stone age" but I may have taken it slightly too literally. But I really would like to have more control over Linux memory use, because it does cause bad behaviour at times. If I have 4GB of RAM, I'd like to set 200MB or so aside for programs, and never page out the window I'm going to uncover later. Likewise when I write a DVD image, I would like to avoid buffering a few GB without i/o and then driving the disk totally busy while it gets written out (after it has pushed out things I will use again).

The old 2.4.x-aa kernels had some tunables to make the kernel aggressive about writing pages to disk quickly, and I haven't been able to match that behaviour without patches in 2.6. I may be missing a tunable, but swappiness doesn't seem to be the one I want. I have a patch I'm playing with, but it's not ready for prime time, and is probably counter to the current philosophy of memory management.

Thanks for clarifying.

--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979

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