Re: [RFC] Free up page->private for compound pages

[Dave Kleikamp <shaggy@linux.vnet.ibm.com>]

On Wed, 2007-04-04 at 20:19 -0700, Christoph Lameter wrote:

> Index: linux-2.6.21-rc5-mm4/include/linux/page-flags.h
> ===================================================================
> --- linux-2.6.21-rc5-mm4.orig/include/linux/page-flags.h	2007-04-03 23:48:34.000000000 -0700
> +++ linux-2.6.21-rc5-mm4/include/linux/page-flags.h	2007-04-04 18:25:47.000000000 -0700
> @@ -91,6 +91,7 @@
>  #define PG_booked		20	/* Has blocks reserved on-disk */
> 
>  #define PG_readahead		21	/* Reminder to do read-ahead */
> +#define PG_tail			22	/* Tail portion of a compound page */
> 
>  /* PG_owner_priv_1 users should have descriptive aliases */
>  #define PG_checked		PG_owner_priv_1 /* Used by some filesystems */
> @@ -214,6 +215,10 @@ static inline void SetPageUptodate(struc
>  #define __SetPageCompound(page)	__set_bit(PG_compound, &(page)->flags)
>  #define __ClearPageCompound(page) __clear_bit(PG_compound, &(page)->flags)
> 
> +#define PageTail(page)	test_bit(PG_tail, &(page)->flags)
> +#define __SetPageTail(page)	__set_bit(PG_tail, &(page)->flags)
> +#define __ClearPageTail(page)	__clear_bit(PG_tail, &(page)->flags)
> +
>  #ifdef CONFIG_SWAP
>  #define PageSwapCache(page)	test_bit(PG_swapcache, &(page)->flags)
>  #define SetPageSwapCache(page)	set_bit(PG_swapcache, &(page)->flags)

Wow, I was planning on adding that exact flag for the work I'm doing
with Page Cache Tails:
http://kernel.org/pub/linux/kernel/people/shaggy/OLS-2006/

I'm working on killing the page flag, but I am still using PageTail() to
test for the special-case page.  No worry.  I'll rename it to something
less ambiguous.

As far as the Page Cache Tail work, I'll try to get some patches out for
review soon.

Shaggy
-- 
David Kleikamp
IBM Linux Technology Center

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