Re: Ramdisk for > 1GB / >2 GB

[ebiederm+eric@ccr.net (Eric W. Biederman)]

>>>>> "MS" == Manfred Spraul <masp0008@stud.uni-sb.de> writes:

MS> I've written a ramdisk driver that can use physical, unmapped memory. I've
MS> posted a beta version this morning to linux-kernel.
MS> Basically, it is a kernel patch that manages the memory (alloc_hugemem(),
MS> free_hugemem()), and a block device driver that can use this memory.

MS> I'm new in the Linux MM, perhaps you could help me on these questions:

MS> 1) SMP:
MS> I use a spinlock for every ramdisk, and one page for each drive as a window
MS> to the physical memory. Since only 1 processor uses this page, I can use
MS> __flush_tlb_one( == INVLPG only on the local processor) without any further
MS> synchronization.

Sounds good.  But it's not my area of expertise.

MS> Is that stable on SMP, and do you think that this parallel enough?

MS> Linus suggested using one 4MB pte for each processor, but I think that this
MS> would be to much overhead.
MS> Another idea would be using a hash table (eg. 32 spinlocks, 32 pages) that
MS> is shared by all processors.

Except for quantity of address space consumed a 4MB pte should be equal to a
4k pte.

MS> 3) Is more than 2 GB memory a problem that only applies to the i386
MS> architecture, or is there demand for that on PowerPC, Sparc32?

It's a problem for 32bit architectures.  Most of the RISC processors (I believe)
have 64bit extensions so it's less of an issue there.

Eric
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