linux-kernel - Re: [PATCH 01/25] tile: Fix __pte_free

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Message-ID: <4D4C63ED.6060104@tilera.com>
Date:	Fri, 4 Feb 2011 15:39:09 -0500
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	<akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
	<linux-mm@...ck.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
Subject: Re: [PATCH 01/25] tile: Fix __pte_free_tlb

On 1/25/2011 12:31 PM, Peter Zijlstra wrote:
> Tile's __pte_free_tlb() implementation makes assumptions about the
> generic mmu_gather implementation, cure this ;-)

I assume you will take this patch into your tree?  If so:

Acked-by: Chris Metcalf <cmetcalf@...era.com>

> [ Chris, from a quick look L2_USER_PGTABLE_PAGES is something like:
>   1 << (24 - 16 + 3), which looks awefully large for an on-stack
>   array. ]

Yes, the pte_pages[] array in this routine is 2KB currently.  Currently we
ship with 64KB pagesize, so the kernel stack has plenty of room.  I do like
that your patch removes this buffer, however, since we're currently looking
into (re-)supporting 4KB pages, which would totally blow the kernel stack
in this routine.

> Cc: Chris Metcalf <cmetcalf@...era.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  arch/tile/mm/pgtable.c |   15 ++-------------
>  1 file changed, 2 insertions(+), 13 deletions(-)
>
> Index: linux-2.6/arch/tile/mm/pgtable.c
> ===================================================================
> --- linux-2.6.orig/arch/tile/mm/pgtable.c
> +++ linux-2.6/arch/tile/mm/pgtable.c
> @@ -252,19 +252,8 @@ void __pte_free_tlb(struct mmu_gather *t
>  	int i;
>  
>  	pgtable_page_dtor(pte);
> -	tlb->need_flush = 1;
> -	if (tlb_fast_mode(tlb)) {
> -		struct page *pte_pages[L2_USER_PGTABLE_PAGES];
> -		for (i = 0; i < L2_USER_PGTABLE_PAGES; ++i)
> -			pte_pages[i] = pte + i;
> -		free_pages_and_swap_cache(pte_pages, L2_USER_PGTABLE_PAGES);
> -		return;
> -	}
> -	for (i = 0; i < L2_USER_PGTABLE_PAGES; ++i) {
> -		tlb->pages[tlb->nr++] = pte + i;
> -		if (tlb->nr >= FREE_PTE_NR)
> -			tlb_flush_mmu(tlb, 0, 0);
> -	}
> +	for (i = 0; i < L2_USER_PGTABLE_PAGES; ++i)
> +		tlb_remove_page(tlb, pte + i);
>  }
>  
>  #ifndef __tilegx__
>
>

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com

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