linux-kernel - Re: [PATCH 2/3] mm: Avoid putting a bad page back on the LRU v6

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Message-ID: <Pine.LNX.4.64.0806091123400.30605@schroedinger.engr.sgi.com>
Date:	Mon, 9 Jun 2008 11:28:00 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Russ Anderson <rja@....com>
cc:	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 2/3] mm: Avoid putting a bad page back on the LRU v6

On Mon, 9 Jun 2008, Russ Anderson wrote:

> -#define PAGE_FLAGS	(1 << PG_lru   | 1 << PG_private   | 1 << PG_locked | \
> +#define PAGE_FLAGS_BASE	(1 << PG_lru   | 1 << PG_private   | 1 << PG_locked | \
>  			 1 << PG_buddy | 1 << PG_writeback | \
>  			 1 << PG_slab  | 1 << PG_swapcache | 1 << PG_active)
> +
> +#ifdef CONFIG_PAGEFLAGS_EXTENDED
> +PAGEFLAG(MemError, memerror)
> +#define	PAGE_FLAGS	(PAGE_FLAGS_BASE | 1UL << PG_memerror)
> +#else
> +PAGEFLAG_FALSE(MemError)
> +#define	PAGE_FLAGS	(PAGE_FLAGS_BASE)
> +#endif

Hmmmm... That doesnt look nice. It would be good if we had some definition 
that  allows the simple oring with a flag mask. That mask should be 
zero if the flag is always false.

#ifdef CONFIG_PAGEFLAGS_EXTENDED
PAGEFLAG(MemError, memerror)
#define MemError_mask (1 << PG_memerror)
#else
PAGEFLAG_FALSE(MemError)
#define MemError_mask 0
#endif

#define	PAGE_FLAGS	(PAGE_FLAGS_BASE | MemError_mask)

Maybe we could have the PAGEFLAG and the PAGEFLAG_FALSE macros generate 
these definitions?

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