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

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Message-ID: <20121024093510.GB23775@mudshark.cambridge.arm.com>
Date:	Wed, 24 Oct 2012 10:35:10 +0100
From:	Will Deacon <will.deacon@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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, Oct 23, 2012 at 10:50:27PM +0100, Andrew Morton wrote:
> On Tue, 23 Oct 2012 11:11:25 +0100
> Will Deacon <will.deacon@....com> wrote:
> > 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?

I think DaveM may want this patch for sparc, so I'll keep it separate from
the ARM patches and have a go at reworking it when the sched-numa stuff has
settled down. Is that all in linux-next btw? If so, I can use that as a
starting point to dealing with the mess.

Cheers,

Will
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