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

Anthony Liguori
2008-03-20T14:04:17Z

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