Re: [PATCH 12/16] mm: fold sc.may_writepage and sc.may_swap intosc.flags

[Nick Piggin]

Wu Fengguang wrote:
> Fold bool values into flags to make struct scan_control more compact.

Probably not a bad idea (although you haven't done anything for 64-bit
archs, yet)... do we wait until one more flag wants to be added?

> Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxxx>
> ---
>
>  mm/vmscan.c |   22 ++++++++++------------
>  1 files changed, 10 insertions(+), 12 deletions(-)
>
> --- linux.orig/mm/vmscan.c
> +++ linux/mm/vmscan.c
> @@ -72,12 +72,12 @@ struct scan_control {
>  	/* This context's GFP mask */
>  	gfp_t gfp_mask;
>  
> -	int may_writepage;
> -
> -	/* Can pages be swapped as part of reclaim? */
> -	int may_swap;
> +	unsigned long flags;
>  };
>  
> +#define SC_MAY_WRITEPAGE	0x1
> +#define SC_MAY_SWAP		0x2	/* Can pages be swapped as part of reclaim? */
> +
>  #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
>  
>  #ifdef ARCH_HAS_PREFETCH
> @@ -488,7 +488,7 @@ static int shrink_list(struct list_head 
>  		 * Try to allocate it some swap space here.
>  		 */
>  		if (PageAnon(page) && !PageSwapCache(page)) {
> -			if (!sc->may_swap)
> +			if (!(sc->flags & SC_MAY_SWAP))
>  				goto keep_locked;
>  			if (!add_to_swap(page, GFP_ATOMIC))
>  				goto activate_locked;
> @@ -519,7 +519,7 @@ static int shrink_list(struct list_head 
>  				goto keep_locked;
>  			if (!may_enter_fs)
>  				goto keep_locked;
> -			if (laptop_mode && !sc->may_writepage)
> +			if (laptop_mode && !(sc->flags & SC_MAY_WRITEPAGE))
>  				goto keep_locked;
>  
>  			/* Page is dirty, try to write it out here */
> @@ -1238,8 +1238,7 @@ int try_to_free_pages(struct zone **zone
>  	delay_prefetch();
>  
>  	sc.gfp_mask = gfp_mask;
> -	sc.may_writepage = 0;
> -	sc.may_swap = 1;
> +	sc.flags = SC_MAY_SWAP;
>  	sc.nr_scanned = 0;
>  	sc.nr_reclaimed = 0;
>  
> @@ -1287,7 +1286,7 @@ int try_to_free_pages(struct zone **zone
>  		 */
>  		if (sc.nr_scanned > SWAP_CLUSTER_MAX * 3 / 2) {
>  			wakeup_pdflush(laptop_mode ? 0 : sc.nr_scanned);
> -			sc.may_writepage = 1;
> +			sc.flags |= SC_MAY_WRITEPAGE;
>  		}
>  
>  		/* Take a nap, wait for some writeback to complete */
> @@ -1343,8 +1342,7 @@ static int balance_pgdat(pg_data_t *pgda
>  
>  loop_again:
>  	sc.gfp_mask = GFP_KERNEL;
> -	sc.may_writepage = 0;
> -	sc.may_swap = 1;
> +	sc.flags = SC_MAY_SWAP;
>  	sc.nr_mapped = read_page_state(nr_mapped);
>  	sc.nr_scanned = 0;
>  	sc.nr_reclaimed = 0;
> @@ -1439,7 +1437,7 @@ scan_swspd:
>  		 */
>  		if (sc.nr_scanned > SWAP_CLUSTER_MAX * 2 &&
>  		    sc.nr_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
> -			sc.may_writepage = 1;
> +			sc.flags |= SC_MAY_WRITEPAGE;
>  
>  		if (nr_pages && to_free > sc.nr_reclaimed)
>  			continue;	/* swsusp: need to do more work */

--
SUSE Labs, Novell Inc.
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