On Thu, 18 August 2005 12:41:32 +0200, Folkert van Heusden wrote: > > > Just use mmap(). Unlike your proposal, it cooperates with the page > > cache. > > Doesn't that one also use copying? I've also heard that using mmap is > expensive due to pagefaulting. I've found, for example, that copying a > 1.3GB file using read/write instead of mmap & memcpy is seconds faster.
Since you don't consider device DMA to be a copy, no, it doesn't. The data is transferred into page cache, then the pages are mapped into your processes memory without an additional copy. The pagefaulting isn't free either, I agree. And for streaming accesses like your copy of a large file, taking one fault per 4k copied is not an ideal case. Most likely you'd want Linus' pipe stuff for copying a large file without ever looking at the data. That work is still unfinished, though, and I'm currently lacking time to work on it. Jörn -- He that composes himself is wiser than he that composes a book. -- B. Franklin - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
