Messages in this thread |  | | | Date | Wed, 19 May 2010 08:30:10 -0700 (PDT) | | From | Linus Torvalds <> | | Subject | Re: Unexpected splice "always copy" behavior observed |
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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
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