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

[Anthony Liguori]

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Rusty Russell wrote:
>>  
>>> From: Paul TBBle Hampson <Paul.Hampson at Pobox.com>
>>>
>>> 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.
>>   
>
> Surely the difference disappears once the pages have been faulted in?

I don't recall.  I believe rewrite was okay but initial write was much 
worse.

Regards,

Anthony Liguori