Re: [patch 6/12] hold atomic kmaps across generic_file_read

[Albert D. Cahalan]

Jeff Garzik writes:
> Linus Torvalds wrote:

> The overhead of the extra stat and mmap/munmap syscalls seemed to be the 
> thing that slowed things down.  sendfile was pretty fast, but still an 
> extra syscall, with an annoyingly large error handling case [only 
> certain files can be sendfile'd]

That error handling case sure does discourage sendfile use.

> I sure would like an O_STREAMING flag, though...  let a user app hint to 
> the system that the pages it is reading or writing are perhaps less 
> likely to be reused, or access randomly....  A copy-file syscall would 
> be nice, too, but that's just laziness talking....

You have a laptop computer with a USB-connected Ethernet.
You mount a NetApp or similar box via the SMB/CIFS protocol.
You see a multi-gigabyte file. You make a copy... ouch!!!
For each gigabyte, you hog the network for an hour.

Now let's say this file is for a MacOS app. You have to
preserve the creator, file type, resource fork, etc.