Re: changes to kiobuf support in 2.4.(?)4

[Andrea Arcangeli]

On Thu, Aug 02, 2001 at 12:31:52AM -0700, Jeremy Higdon wrote:
> By "mmap callback", you're referring to the mmap entry in the file_operations
> structure?

yes.

> I am doing direct I/O.  I'm using the kiobuf to hold the page addresses
> of the user's data buffer, but I'm calling directly into my driver
> after doing the map_user_kiobuf() (I have a read/write request, a file
> offset, a byte count, and a set of pages to DMA into/out of, and that
> gets directly translated into a SCSI command).
> 
> It turns out that the old kmem_cache_alloc was very lightweight, so I
> could get away with doing it once per I/O request, so I would indeed
> profit by going back to a light weight kiobuf, or at least an optional
> allocation of the bh and blocks arrays (perhaps turn them into pointers
> to arrays?).

I see your problem and it's a valid point indeed. But could you actually
allocate the kiobuf in the file->f_iobuf pointer? I mean: could you
allocate it at open/close too?  That would be the way I prefer since you
would need to allocate the bh anyways later (but with a flood of
alloc/free). So if you could move the kiobufs allocation out of the fast
path you would get a benefit too I believe.

Andrea