Re: [kvm-devel] [RFC PATCH 1/5] lguest: mmap backing file

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

Rusty Russell wrote:
> From: Paul TBBle Hampson <Paul.Hampson-vM6MUUi4OUAAvxtiuMwx3w@public.gmane.org>
>
> This creates a file in $HOME/.lguest/ to directly back the RAM and DMA memory
> mappings created by map_zeroed_pages.
>   

I created a test program recently that measured the latency of a 
reads/writes to an mmap() file in /dev/shm and in a normal filesystem.  
Even after unlinking the underlying file, the write latency was much 
better with a mmap()'d file in /dev/shm.

/dev/shm is not really for general use.  I think we'll want to have our 
own tmpfs mount that we use to create VM images.  I also prefer to use a 
unix socket for communication, unlink the file immediately after open, 
and then pass the fd via SCM_RIGHTS to the other process.

Regards,

Anthony Liguori