Re: Unexpected splice "always copy" behavior observed

[Linus Torvalds]

On Thu, 20 May 2010, Nick Piggin wrote:
> 
> Well I mean a full invalidate -- invalidate_mapping_pages -- so there is
> literally no pagecache there at all.

Umm. That won't work. Think mapped pages. You can't handle them 
atomically, so somebody will page-fault them in.

So you'd have to have a "invalidate_and_replace()" to do it atomically 
while holding the mapping spinlock or something. 

And WHAT IS THE POINT? That will be about a million times slower than 
just doing the effing copy in the first place!

Memory copies are _not_ slow. Not compared to taking locks and doing TLB 
invalidates.

		Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/