linux-kernel - Re: [RFC 13/26] SLUB: Add SlabReclaimable() to avoid repeated reclaim attempts

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Date:	Wed, 19 Sep 2007 11:08:28 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Christoph Lameter <clameter@....com>
CC:	Andy Whitcroft <apw@...dowen.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	Christoph Hellwig <hch@....de>, Mel Gorman <mel@...net.ie>,
	David Chinner <dgc@....com>
Subject: Re: [RFC 13/26] SLUB: Add SlabReclaimable() to avoid repeated reclaim
 attempts

Christoph Lameter wrote:
> Add a flag SlabReclaimable() that is set on slabs with a method
> that allows defrag/reclaim. Clear the flag if a reclaim action is not
> successful in reducing the number of objects in a slab. The reclaim
> flag is set again if all objects have been allocated from it.
> 
> Signed-off-by: Christoph Lameter <clameter@....com>
> ---
>  mm/slub.c |   42 ++++++++++++++++++++++++++++++++++++------
>  1 file changed, 36 insertions(+), 6 deletions(-)
> 
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c	2007-08-28 20:10:37.000000000 -0700
> +++ linux-2.6/mm/slub.c	2007-08-28 20:10:47.000000000 -0700
> @@ -107,6 +107,8 @@
>  #define SLABDEBUG 0
>  #endif
>  
> +#define SLABRECLAIMABLE (1 << PG_dirty)
> +
>  static inline int SlabFrozen(struct page *page)
>  {
>  	return page->flags & FROZEN;
> @@ -137,6 +139,21 @@ static inline void ClearSlabDebug(struct
>  	page->flags &= ~SLABDEBUG;
>  }
>  
> +static inline int SlabReclaimable(struct page *page)
> +{
> +	return page->flags & SLABRECLAIMABLE;
> +}
> +
> +static inline void SetSlabReclaimable(struct page *page)
> +{
> +	page->flags |= SLABRECLAIMABLE;
> +}
> +
> +static inline void ClearSlabReclaimable(struct page *page)
> +{
> +	page->flags &= ~SLABRECLAIMABLE;
> +}

Why is it safe to not use the normal page flag bit operators
for these page flags operations?

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