Re: Implementing NVMHCI...

[Jeff Garzik <jeff@garzik.org>]

Alan Cox wrote:
>> We've abstract the DMA mapping/SG list handling enough that the
>> block size should make no more difference than it does for the
>> MTU size of a network.
> 
> You need to start managing groups of pages in the vm and keeping them
> together and writing them out together and paging them together even if
> one of them is dirty and the other isn't. You have to deal with cases
> where a process forks and the two pages are dirtied one in each but still
> have to be written together.
> 
> Alternatively you go for read-modify-write (nasty performance hit
> especially for RAID or a log structured fs).

Or just ignore the extra length, thereby excising the 'read-modify' 
step...  Total storage is halved or worse, but you don't take as much of 
a performance hit.

	Jeff