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Content-ID: <Pine.LNX.3.91.960709230737.304C@mayday.compulink.co.uk>
This seems to have gone missing ... lets try again ...
-- Rob. (Robert de Bath <robert@mayday.compulink.co.uk>)---------- Forwarded message ---------- Date: Tue, 9 Jul 1996 23:16:46 +0100 (BST) From: Robert de Bath <robert@mayday.compulink.co.uk> To: Eric Thelin <erict@goodnet.com>, Derrik Pates <dpates@Cavern.NMSU.Edu>, Chad Page <page0588@sundance.sjsu.edu>, "Theodore Y. Ts'o" <tytso@MIT.EDU>, Paul Gortmaker <gpg109@rsphy1.anu.edu.au>, Systemkennung Linux <linux@mailhost.uni-koblenz.de>, Scott Laird <scott@laird.com> Cc: linux-kernel@vger.rutgers.edu Subject: Re: Old style ramdisk
On Mon, 8 Jul 1996, Derrik Pates wrote:
> > running programs from the slooow RAM, 2.0.0 ends up about 1/4 the speed > > of 1.2.13 on an already very slow machine. > > Why? You take away from the memory to create a swapfile to swap pages from > memory? I think that's a bit redundant, not to mention wasteful. That's > like creating a RAM disk to put your WinSlows 3.1 swapfile on. 'Cause the ISA ram is a (tiny) fraction of the speed of the 32 bit stuff. Also, I have put a windows swap file on a ramdisk before ... it was a HW EMS card so windoze couldn't use it any other way. :-)
On Mon, 8 Jul 1996, Chad Page wrote:
> Buffer-cache experts : Is there any way to create buffer-heads > arbitrarily? If so, then at system startup it *might* be possible to > allocate the memory, and create a ramdisk (or more than 1, depending on > the # of fragments) which contains the 'slow' areas of memory using the > current driver. Now this I like, but does it have to even be one ramdisk per fragment? As I understand it the new ramdisks are 100% fragmented anyway so you _should_ be able to assign them all to one 'disk', or assign this RAM to some sort of pool that can only be allocated by the ramdisks ...
Actually, thinking about this if a block is in the buffer bool it'll be mmapped into processes by Linux, we don't want this, we specifically want the data to be copied to a low buffer before anything is done AFAICS the only way to do this is a memcpy in the device driver.
> The old-style ramdisk actually took memory away from the kernel's > reach (I think it lowered the top of memory), so it was never really > modularizable (then again, it was written long before modules even > existed ;) Well, it can be 'modularized' _but_ if it is it can only use memory outside that which has been grabbed by Linux. That's not a problem and could even be useful if you have disjoint chunks of RAM.
On Mon, 8 Jul 1996, Theodore Y. Ts'o wrote:
> What I would do: > > 1. ... append="mem=2M"
> 2. Take the old ramdisk driver, and modify it to be loadable as a > kernel module. Step (1) above means that you won't have to do any nasty > boot-time memory allocation, so it will be easy to drop it as a loadable > kernel module. This is _exactly_ what I was thinking of, of course there's the tiny problem that I haven't actually done that much Linux kernel programming and don't know what the current module recipe is ... :-)
On Tue, 9 Jul 1996, Paul Gortmaker wrote: > It should be a two second operation to add the old ramdisk source file > from a pre 1.3.47 (I think) kernel back into the 2.0.x tree. Make sure > you *don't* compile in the new ramdisk driver as well, or there will be > a conflict for the minor number associated with /dev/ram Humm, This does look like the simplest solution, but it's not very pretty...
LATER: Ok! I've found a nice solution. What I've done is to make some small changes to the code for initrd. There's now a boot option "initrd=x,y" the values are the start and end addresses of the ramdisk in kbytes.
The initrd is now writeable and _if_ you write to it it will not be released until/unless you do a BLKFLSBUF and close.
It even works on this nice large machine ... 16Mb of RAM 64Mb of RAM swap ...
Of course all I need now is some way to tell Linux that it's faster to save clean pages to this swap than it is to re-read them from the HD... :-)
-- Rob. 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