linux-kernel - Re: [PATCH v2] mm: thp: Set the accessed flag for old pages on access fault.

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Message-Id: <20121023145027.40710e7a.akpm@linux-foundation.org>
Date:	Tue, 23 Oct 2012 14:50:27 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Will Deacon <will.deacon@....com>
Cc:	David Miller <davem@...emloft.net>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"mhocko@...e.cz" <mhocko@...e.cz>,
	"kirill@...temov.name" <kirill@...temov.name>,
	"aarcange@...hat.com" <aarcange@...hat.com>,
	"cmetcalf@...era.com" <cmetcalf@...era.com>,
	Steve Capper <Steve.Capper@....com>
Subject: Re: [PATCH v2] mm: thp: Set the accessed flag for old pages on
 access fault.

On Tue, 23 Oct 2012 11:11:25 +0100
Will Deacon <will.deacon@....com> wrote:

> On Mon, Oct 22, 2012 at 07:18:43PM +0100, Andrew Morton wrote:
> > On Mon, 22 Oct 2012 11:35:03 +0100
> > Will Deacon <will.deacon@....com> wrote:
> > 
> > > On Fri, Oct 19, 2012 at 07:49:55PM +0100, Andrew Morton wrote:
> > > > Ho hum.  I'll drop
> > > > mm-thp-set-the-accessed-flag-for-old-pages-on-access-fault.patch and
> > > > shall assume that you'll sort things out at the appropriate time.
> > > 
> > > Happy to sort it out once I work out what's going wrong!
> > 
> > The patch "ARM: mm: Transparent huge page support for LPAE systems" is
> > not present in linux-next, so this patch ("mm: thp: Set the accessed
> > flag for old pages on access fault") will not compile?
> 
> This patch ("mm: thp: Set the accessed flag for old pages on access fault")
> doesn't depend on "ARM: mm: Transparent huge page support for LPAE systems"
> because currently transparent huge pages cannot be enabled for ARM in
> mainline (or linux-next). update_mmu_cache_pmd is only called from
> mm/huge_memory.c, which depends on CONFIG_TRANSPARENT_HUGEPAGE=y.
> 
> As for the new huge_pmd_set_accessed function... there's a similar situation
> for the do_huge_pmd_wp_page function: it's called from mm/memory.c but is
> only defined in mm/huge_memory.c. Looks like the compiler optimises those
> calls away because pmd_trans_huge and friends constant-fold to 0.

Ah, OK.

"mm: thp: Set the accessed flag for old pages on access fault" clashes
in a non-trivial way with linux-next changes, due to the sched-numa
changes (sigh).  This is a problem for me, because I either need to
significantly alter your patch (so it isn't applicable to mainline) or
I need to stage your patch ahead of linux-next, then fix up linux-next
every day after I've pulled and re-merged it.

I'm unsure what your timing is.  Can you carry "mm: thp: Set the
accessed flag for old pages on access fault" until either the whole
patchset is ready to merge or until the sched-numa situation has been
cleared up?
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