Re: [openib-general] Re: [PATCH repost] PROT_DONTCOPY: ifiniband uverbs fork support

[Gleb Natapov]

On Thu, Aug 11, 2005 at 03:04:29PM +0100, Hugh Dickins wrote:
> On Thu, 11 Aug 2005, Gleb Natapov wrote:
> > What about the idea that was floating around about new VM flag that will
> > instruct kernel to copy pages belonging to the vma on fork instead of mark
> > them as cow?
> 
> It's a pretty good idea, and thanks for reminding us of it.
> 
> It suffers from the general difficulty with fixes within get_user_pages,
> that we need down_write(&mm->mmap_sem) to split_vma, and even just to
> update vm_flags, whereas get_user_pages is entered with down_read.
> 
Why do it form get_user_pages? Lets use madvise/mprotect interface.
Program can mrpotect(VM_COPYONFORK) address range before registering it.

--
			Gleb.
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