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

[Michael S. Tsirkin]

Quoting r. Hugh Dickins <hugh at veritas.com>:
> Subject: Re: [openib-general] Re: [PATCH repost] PROT_DONTCOPY: ifiniband uverbs fork support
> 
> 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.

No, the idea is to let the application (or a library that it loades)
change this flag by means of some system call.
Something like MADV_COPYONFORK, in addition to MADV_DONTCOPY.


-- 
MST