Re: [RFC] mmaped copy too slow?

KOSAKI Motohiro
2008-01-15T03:20:27Z

Hi Rik

> While being able to deal with used-once mappings in page reclaim
> could be a good idea, this would require us to be able to determine
> the difference between a page that was accessed once since it was
> faulted in and a page that got accessed several times.

it makes sense that read ahead hit assume used-once mapping, may be.
I will try it.

(may be, i can repost soon)

> Given that page faults have overhead too, it does not surprise me
> that read+write is faster than mmap+memcpy.
>
> In threaded applications, page fault overhead will be worse still,
> since the TLBs need to be synchronized between CPUs (at least at
> reclaim time).

sure.
but current is unnecessary large performance difference.
I hope improvement it because copy by mmapd is very common operation.

> Maybe we should just advise people to use read+write, since it is
> faster than mmap+memcpy?

Time is solved to it :)
thanks!

- kosaki