linux-kernel - Re: [PATCH 17/50] mm: Do not flush TLB during protection change if !pte_present && !migration

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Date:	Tue, 17 Sep 2013 18:00:32 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 17/50] mm: Do not flush TLB during protection change if
 !pte_present && !migration_entry

On Mon, Sep 16, 2013 at 06:35:47PM +0200, Peter Zijlstra wrote:
> On Tue, Sep 10, 2013 at 10:31:57AM +0100, Mel Gorman wrote:
> > NUMA PTE scanning is expensive both in terms of the scanning itself and
> > the TLB flush if there are any updates. Currently non-present PTEs are
> > accounted for as an update and incurring a TLB flush where it is only
> > necessary for anonymous migration entries. This patch addresses the
> > problem and should reduce TLB flushes.
> > 
> > Signed-off-by: Mel Gorman <mgorman@...e.de>
> > ---
> >  mm/mprotect.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/mprotect.c b/mm/mprotect.c
> > index 1f9b54b..1e9cef0 100644
> > --- a/mm/mprotect.c
> > +++ b/mm/mprotect.c
> > @@ -109,8 +109,9 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> >  				make_migration_entry_read(&entry);
> >  				set_pte_at(mm, addr, pte,
> >  					swp_entry_to_pte(entry));
> > +
> > +				pages++;
> >  			}
> > -			pages++;
> >  		}
> >  	} while (pte++, addr += PAGE_SIZE, addr != end);
> >  	arch_leave_lazy_mmu_mode();
> 
> Should we fold this into patch 7 ?

Looking closer at it, I think folding it into the patch would overload
the purpose of patch 7 a little too much but I shuffled the series to
keep the patches together.

-- 
Mel Gorman
SUSE Labs
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