Re: Bugs and wishes in memory management area

Jon Tombs (
Tue, 26 Nov 1996 01:50:16 +0100 (MET)

Jean Francois Martinez said:

> The spirit of LINUX is trying to make an EFFICIENT OS. I quote Linus
> here: "LINUX is so fast it can do infinite loops, on less than 5
> seconds". I suppose it is still less in an Alpha. :-) Allocating 1
> Meg of memory just to have it at hand if we need to do ISA DMA is the
> kind of corner cutting who leads to needing 128 Meg just to run
> "Hello, world\n", on commercial Unixes.
> People who use old machine can run Linux with less than 16 MB, but they
> must be very carefull with programs being actually loaded.
> For those systems ISA/DMA is possible with all the memory space.
> So ISA/DMA complexity is off topic.

One of the silly things in this thread is the flashy PCI owners who seem
convinced the linux DMA problem is just with out of date ISA systems, and
therefore doesn't need fixing.

This is not the case, get_dma_pages can also fail on your 1GB PCI systems. If
you make a request for 32k of DMA memory, and by over commitment linux has the
32k but it isn't suitable for DMA (not contiguous for example), then it will
still return NULL, ISA or PCI. We really should be able to request DMA memory
in a non ATOMIC fashion regardless of the restraints of the DMA archetecture.
most systems that are failing to install modules, don't have have more than
16MB and an ISA bus, they just have most of the memory that is installed
inuse, and no single block of free ram avaiable.

Also how many PCI owners use only PCI sound cards, ethernet adapters and tape
streamers. Like it or not ISA dma is still used by much of todays hardware.

Jon. <,>