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

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Message-ID: <20130916163547.GF9326@twins.programming.kicks-ass.net>
Date:	Mon, 16 Sep 2013 18:35:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mgorman@...e.de>
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 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 ?
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