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

Anthony Liguori
2008-03-20T15:24:15Z

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Rusty Russell wrote:
>>
>>> From: Paul TBBle Hampson <Paul.Hampson@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

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