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Date:	Tue, 7 Oct 2014 11:46:04 +0100
From:	"Dr. David Alan Gilbert" <>
To:	"Kirill A. Shutemov" <>
Cc:	Andrea Arcangeli <>,,,,,,
	Linus Torvalds <>,
	Andres Lagar-Cavilla <>,
	Dave Hansen <>,
	Paolo Bonzini <>,
	Rik van Riel <>, Mel Gorman <>,
	Andy Lutomirski <>,
	Andrew Morton <>,
	Sasha Levin <>,
	Hugh Dickins <>,
	Peter Feiner <>,
	"\\\"Dr. David Alan Gilbert\\\"" <>,
	Christopher Covington <>,
	Johannes Weiner <>,
	Android Kernel Team <>,
	Robert Love <>,
	Dmitry Adamushko <>,
	Neil Brown <>, Mike Hommey <>,
	Taras Glek <>, Jan Kara <>,
	KOSAKI Motohiro <>,
	Michel Lespinasse <>,
	Minchan Kim <>,
	Keith Packard <>,
	"Huangpeng (Peter)" <>,
	Isaku Yamahata <>,
	Anthony Liguori <>,
	Stefan Hajnoczi <>,
	Wenchao Xia <>,
	Andrew Jones <>,
	Juan Quintela <>
Subject: Re: [PATCH 08/17] mm: madvise MADV_USERFAULT

* Kirill A. Shutemov ( wrote:
> On Fri, Oct 03, 2014 at 07:07:58PM +0200, Andrea Arcangeli wrote:
> > MADV_USERFAULT is a new madvise flag that will set VM_USERFAULT in the
> > vma flags. Whenever VM_USERFAULT is set in an anonymous vma, if
> > userland touches a still unmapped virtual address, a sigbus signal is
> > sent instead of allocating a new page. The sigbus signal handler will
> > then resolve the page fault in userland by calling the
> > remap_anon_pages syscall.
> Hm. I wounder if this functionality really fits madvise(2) interface: as
> far as I understand it, it provides a way to give a *hint* to kernel which
> may or may not trigger an action from kernel side. I don't think an
> application will behaive reasonably if kernel ignore the *advise* and will
> not send SIGBUS, but allocate memory.

Aren't DONTNEED and DONTDUMP  similar cases of madvise operations that are
expected to do what they say ?

> I would suggest to consider to use some other interface for the
> functionality: a new syscall or, perhaps, mprotect().


> -- 
>  Kirill A. Shutemov
Dr. David Alan Gilbert / / Manchester, UK
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