On Wed, May 19, 2010 at 08:30:10AM -0700, Linus Torvalds wrote: > > > 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. No I never thought it would be a good idea to try to avoid all races or anything. Obviously some cases *cannot* be easily invalidated, if there is a ref on the page or whatever, so the fallback code has to be there anyway. So you would just invalidate and try to insert your page. 99.something% of the time it will work fine. If the insert fails, fall back to copying. And hey you *may* even want a heuristic that avoids trying to invalidate if the page is mapped, due to cost of TLB flushing and faulting etc. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>