linux-kernel - Re: [PATCHv4 02/10] mm: convert mm->nr_ptes to atomic

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Message-ID: <5245EEAD.7010901@linux.vnet.ibm.com>
Date:	Fri, 27 Sep 2013 13:46:37 -0700
From:	Cody P Schafer <cody@...ux.vnet.ibm.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Alex Thorlton <athorlton@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
CC:	"Eric W . Biederman" <ebiederm@...ssion.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Dave Jones <davej@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Kees Cook <keescook@...omium.org>,
	Mel Gorman <mgorman@...e.de>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Robin Holt <robinmholt@...il.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv4 02/10] mm: convert mm->nr_ptes to atomic_t

On 09/27/2013 06:16 AM, Kirill A. Shutemov wrote:
> With split page table lock for PMD level we can't hold
> mm->page_table_lock while updating nr_ptes.
>
> Let's convert it to atomic_t to avoid races.
>

> ---

> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 84e0c56e1e..99f19e850d 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -339,6 +339,7 @@ struct mm_struct {
>   	pgd_t * pgd;
>   	atomic_t mm_users;			/* How many users with user space? */
>   	atomic_t mm_count;			/* How many references to "struct mm_struct" (users count as 1) */
> +	atomic_t nr_ptes;			/* Page table pages */
>   	int map_count;				/* number of VMAs */
>
>   	spinlock_t page_table_lock;		/* Protects page tables and some counters */
> @@ -360,7 +361,6 @@ struct mm_struct {
>   	unsigned long exec_vm;		/* VM_EXEC & ~VM_WRITE */
>   	unsigned long stack_vm;		/* VM_GROWSUP/DOWN */
>   	unsigned long def_flags;
> -	unsigned long nr_ptes;		/* Page table pages */
>   	unsigned long start_code, end_code, start_data, end_data;
>   	unsigned long start_brk, brk, start_stack;
>   	unsigned long arg_start, arg_end, env_start, env_end;

Will 32bits always be enough here? Should atomic_long_t be used instead?

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