linux-kernel - Re: [PATCH] mm: Fix the TLB range flushed when __tlb_remove

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Message-ID: <20130529140319.GK17767@MacBook-Pro.local>
Date:	Wed, 29 May 2013 15:03:19 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Max Filippov <jcmvbkbc@...il.com>
Subject: Re: [PATCH] mm: Fix the TLB range flushed when __tlb_remove_page()
 runs out of slots

On Wed, May 29, 2013 at 01:56:13PM +0100, Vineet Gupta wrote:
> zap_pte_range loops from @addr to @end. In the middle, if it runs out of
> batching slots, TLB entries needs to be flushed for @start to @interim,
> NOT @interim to @end.
> 
> Since ARC port doesn't use page free batching I can't test it myself but
> this seems like the right thing to do.
> Observed this when working on a fix for the issue at thread:
> 	http://www.spinics.net/lists/linux-arch/msg21736.html
> 
> Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: linux-mm@...ck.org
> Cc: linux-arch@...r.kernel.org <linux-arch@...r.kernel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Max Filippov <jcmvbkbc@...il.com>
> ---
>  mm/memory.c |    9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 6dc1882..d9d5fd9 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1110,6 +1110,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>  	spinlock_t *ptl;
>  	pte_t *start_pte;
>  	pte_t *pte;
> +	unsigned long range_start = addr;
>  
>  again:
>  	init_rss_vec(rss);
> @@ -1215,12 +1216,14 @@ again:
>  		force_flush = 0;
>  
>  #ifdef HAVE_GENERIC_MMU_GATHER
> -		tlb->start = addr;
> -		tlb->end = end;
> +		tlb->start = range_start;
> +		tlb->end = addr;
>  #endif
>  		tlb_flush_mmu(tlb);
> -		if (addr != end)
> +		if (addr != end) {
> +			range_start = addr;
>  			goto again;
> +		}
>  	}

Isn't this code only run if force_flush != 0? force_flush is set to
!__tlb_remove_page() and this function always returns 1 on (generic TLB)
UP since tlb_fast_mode() is 1. There is no batching on UP with the
generic TLB code.

-- 
Catalin
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