Date: Tue, 9 Jun 2009 11:57:25 +0200
From: Nick Piggin <npiggin@suse.de>
To: Andi Kleen <andi@firstfloor.org>
Cc: Lee.Schermerhorn@hp.com, akpm@linux-foundation.org,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       fengguang.wu@intel.com
Subject: Re: [PATCH] [8/16] HWPOISON: Use bitmask/action code for try_to_unmap behaviour
Message-ID: <20090609095725.GC14820@wotan.suse.de>
References: <20090603846.816684333@firstfloor.org> <20090603184641.868D31D0282@basil.firstfloor.org>
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On Wed, Jun 03, 2009 at 08:46:41PM +0200, Andi Kleen wrote:
> 
> try_to_unmap currently has multiple modi (migration, munlock, normal unmap)
> which are selected by magic flag variables. The logic is not very straight
> forward, because each of these flag change multiple behaviours (e.g.
> migration turns off aging, not only sets up migration ptes etc.)
> Also the different flags interact in magic ways.
> 
> A later patch in this series adds another mode to try_to_unmap, so 
> this becomes quickly unmanageable.
> 
> Replace the different flags with a action code (migration, munlock, munmap)
> and some additional flags as modifiers (ignore mlock, ignore aging).
> This makes the logic more straight forward and allows easier extension
> to new behaviours. Change all the caller to declare what they want to 
> do.
> 
> This patch is supposed to be a nop in behaviour. If anyone can prove 
> it is not that would be a bug.
> 
> Cc: Lee.Schermerhorn@hp.com
> Cc: npiggin@suse.de
> 
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> 
> ---
>  include/linux/rmap.h |   14 +++++++++++++-
>  mm/migrate.c         |    2 +-
>  mm/rmap.c            |   40 ++++++++++++++++++++++------------------
>  mm/vmscan.c          |    2 +-
>  4 files changed, 37 insertions(+), 21 deletions(-)
> 
> Index: linux/include/linux/rmap.h
> ===================================================================
> --- linux.orig/include/linux/rmap.h	2009-06-03 19:36:23.000000000 +0200
> +++ linux/include/linux/rmap.h	2009-06-03 20:39:50.000000000 +0200
> @@ -84,7 +84,19 @@
>   * Called from mm/vmscan.c to handle paging out
>   */
>  int page_referenced(struct page *, int is_locked, struct mem_cgroup *cnt);
> -int try_to_unmap(struct page *, int ignore_refs);
> +
> +enum ttu_flags {
> +	TTU_UNMAP = 0,			/* unmap mode */
> +	TTU_MIGRATION = 1,		/* migration mode */
> +	TTU_MUNLOCK = 2,		/* munlock mode */
> +	TTU_ACTION_MASK = 0xff,
> +
> +	TTU_IGNORE_MLOCK = (1 << 8),	/* ignore mlock */
> +	TTU_IGNORE_ACCESS = (1 << 9),	/* don't age */
> +};
> +#define TTU_ACTION(x) ((x) & TTU_ACTION_MASK)

I still think this is nasty and should work like Gfp flags.

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