Re: [patch for playing] 2.5.65 patch to support > 256 disks

[Badari Pulavarty]

Hi All,

I found 2048-byte slab heavy users. 8MB doesn't seem much they all
add up.

size-2048       before:98 after:4095 diff:3997 size:2060 incr:8233820

The problem is with

	sd.c: sd_attach()
		 alloc_disk(16)

alloc_disk() allocates "hd_struct" structure for 15 minors. 
So it is a 84*15 = 1260 byte allocation. They all come from 
2048-byte slabs. Since I have 4000 simulated disks, it uses up 8MB.

Proposed fixes:

1) Make the allocations come from its own slab, instead of
2048-byte slab. (~40% saving).

2) Instead of allocatinf hd_struct structure for all possible partitions,
why not allocated them dynamically, as we see a partition ? This
way we could (in theory) support more than 16 partitions, if needed.

Are there any issues with doing (2) ? 

Thanks,
Badari