Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt

[Christoph Hellwig]

On Mon, Jul 31, 2017 at 09:42:06AM +0200, Christoph Hellwig wrote:
> On Mon, Jul 31, 2017 at 04:36:47PM +0900, Minchan Kim wrote:
> > Do you suggest define something special flag(e.g., SWP_INMEMORY)
> > for in-memory swap to swap_info_struct when swapon time manually
> > or from bdi_queue_someting automatically?
> > And depending the flag of swap_info_struct, use the onstack bio
> > instead of dynamic allocation if the swap device is in-memory?
> 
> Currently swap always just does I/O on a single page as far
> as I can tell, so it can always just use an on-stack bio and
> biovec.

That's for synchronous I/O, aka reads of course.  For writes you'll
need to do a dynamic allocation if they are asynchronous.  But yes,
if we want to force certain devices to be synchronous we'll need
a flag for that.