linux-kernel - Re: [PATCH v8 4/6] mm: mlock: Add mlock flags to enable VM

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Message-ID: <20150828143251.GF5301@dhcp22.suse.cz>
Date:	Fri, 28 Aug 2015 16:32:51 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Eric B Munson <emunson@...mai.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Jonathan Corbet <corbet@....net>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	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-arch@...r.kernel.org,
	linux-api@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v8 4/6] mm: mlock: Add mlock flags to enable
 VM_LOCKONFAULT usage

On Fri 28-08-15 16:31:30, Michal Hocko wrote:
> On Wed 26-08-15 14:24:23, Eric B Munson wrote:
> > The previous patch introduced a flag that specified pages in a VMA
> > should be placed on the unevictable LRU, but they should not be made
> > present when the area is created.  This patch adds the ability to set
> > this state via the new mlock system calls.
> > 
> > We add MLOCK_ONFAULT for mlock2 and MCL_ONFAULT for mlockall.
> > MLOCK_ONFAULT will set the VM_LOCKONFAULT modifier for VM_LOCKED.
> > MCL_ONFAULT should be used as a modifier to the two other mlockall
> > flags.  When used with MCL_CURRENT, all current mappings will be marked
> > with VM_LOCKED | VM_LOCKONFAULT.  When used with MCL_FUTURE, the
> > mm->def_flags will be marked with VM_LOCKED | VM_LOCKONFAULT.  When used
> > with both MCL_CURRENT and MCL_FUTURE, all current mappings and
> > mm->def_flags will be marked with VM_LOCKED | VM_LOCKONFAULT.
> > 
> > Prior to this patch, mlockall() will unconditionally clear the
> > mm->def_flags any time it is called without MCL_FUTURE.  This behavior
> > is maintained after adding MCL_ONFAULT.  If a call to
> > mlockall(MCL_FUTURE) is followed by mlockall(MCL_CURRENT), the
> > mm->def_flags will be cleared and new VMAs will be unlocked.  This
> > remains true with or without MCL_ONFAULT in either mlockall()
> > invocation.

Btw. I think we really want a man page for this new mlock call.
-- 
Michal Hocko
SUSE Labs
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