swap on eMMC and other flash

[Luca Porzio (lporzio)]

Hugh,

Great topics. As per one of Rik original points:

> 4) skip writeout of zero-filled pages - this can be a big help
>     for KVM virtual machines running Windows, since Windows zeroes
>     out free pages;   simply discarding a zero-filled page is not
>     at all simple in the current VM, where we would have to iterate
>     over all the ptes to free the swap entry before being able to
>     free the swap cache page (I am not sure how that locking would
>     even work)
> 
>     with the extra layer of indirection, the locking for this scheme
>     can be trivial - either the faulting process gets the old page,
>     or it gets a new one, either way it'll be zero filled
> 

Since it's KVMs realm here, can't KSM simply solve the zero-filled pages problem avoiding unnecessary burden for the Swap subsystem?

Cheers, 
   Luca