linux-kernel - Re: [PATCH V3 3/5] mm: mlock: Introduce VM_LOCKONFAULT and add mlock flags to enable it

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Message-ID: <20150710161948.GF4669@akamai.com>
Date:	Fri, 10 Jul 2015 12:19:48 -0400
From:	Eric B Munson <emunson@...mai.com>
To:	Jonathan Corbet <corbet@....net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Vlastimil Babka <vbabka@...e.cz>, linux-alpha@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
	linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
	linux-mm@...ck.org, linux-arch@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH V3 3/5] mm: mlock: Introduce VM_LOCKONFAULT and add mlock
 flags to enable it

On Fri, 10 Jul 2015, Jonathan Corbet wrote:

> On Thu, 9 Jul 2015 14:46:35 -0400
> Eric B Munson <emunson@...mai.com> wrote:
> 
> > > One other question...if I call mlock2(MLOCK_ONFAULT) on a range that
> > > already has resident pages, I believe that those pages will not be locked
> > > until they are reclaimed and faulted back in again, right?  I suspect that
> > > could be surprising to users.  
> > 
> > That is the case.  I am looking into what it would take to find only the
> > present pages in a range and lock them, if that is the behavior that is
> > preferred I can include it in the updated series.
> 
> For whatever my $0.02 is worth, I think that should be done.  Otherwise
> the mlock2() interface is essentially nondeterministic; you'll never
> really know if a specific page is locked or not.
> 
> Thanks,
> 
> jon

Okay, I likely won't have the new set out today then.  This change is
more invasive.  IIUC, I need an equivalent to __get_user_page() skips
pages which are not present instead of faulting in and the call chain to
get to it.  Unless there is an easier way that I am missing.

Eric

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