linux-kernel - Re: [PATCH 14/19] mm: mempolicy: Add MPOL_MF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20121113120248.GA8218@suse.de>
Date:	Tue, 13 Nov 2012 12:02:48 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 14/19] mm: mempolicy: Add MPOL_MF_LAZY

On Tue, Nov 13, 2012 at 11:25:55AM +0100, Ingo Molnar wrote:
> 
> * Mel Gorman <mgorman@...e.de> wrote:
> 
> > From: Lee Schermerhorn <lee.schermerhorn@...com>
> > 
> > NOTE: Once again there is a lot of patch stealing and the end result
> > 	is sufficiently different that I had to drop the signed-offs.
> > 	Will re-add if the original authors are ok with that.
> > 
> > This patch adds another mbind() flag to request "lazy migration".  The
> > flag, MPOL_MF_LAZY, modifies MPOL_MF_MOVE* such that the selected
> > pages are marked PROT_NONE. The pages will be migrated in the fault
> > path on "first touch", if the policy dictates at that time.
> > 
> > <SNIP>
> 
> Here you are paying a heavy price for the earlier design 
> mistake, for forking into per arch approach - the NUMA version 
> of change_protection() had to be open-coded:
> 

I considered this when looking at the two trees.

At the time I also had the option of making change_prot_numa() to be a
wrapper around change_protection() and if pte_numa is made generic, that
becomes more attractive.

One of the reasons I went with this version from Andrea's tree is simply
because it does less work than change_protect() but what should be
sufficient for _PAGE_NUMA. I avoid the TLB flush if there are no PTE
updates for example but could shuffle change_protection() and get the
same thing.

> >  include/linux/mm.h             |    3 +
> >  include/uapi/linux/mempolicy.h |   13 ++-
> >  mm/mempolicy.c                 |  176 ++++++++++++++++++++++++++++++++++++----
> >  3 files changed, 174 insertions(+), 18 deletions(-)
> 
> Compare it to the generic version that Peter used:
> 
>  include/uapi/linux/mempolicy.h | 13 ++++++++---
>  mm/mempolicy.c                 | 49 +++++++++++++++++++++++++++---------------
>  2 files changed, 42 insertions(+), 20 deletions(-)
> 
> and the cleanliness and maintainability advantages are obvious.
> 
> So without some really good arguments in favor of your approach 
> NAK on that complex approach really.
> 

I will reimplement around change_protection() and see what effect, if any,
it has on overhead.

-- 
Mel Gorman
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/