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Date: Mon, 04 May 2009 10:26:18 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Wu Fengguang <fengguang.wu@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
"lee.schermerhorn@...com" <lee.schermerhorn@...com>,
"riel@...hat.com" <riel@...hat.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
Nick Piggin <npiggin@...e.de>,
Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] vmscan: cleanup the scan batching code
On Sat, 2009-05-02 at 10:31 +0800, Wu Fengguang wrote:
> The vmscan batching logic is twisting. Move it into a standalone
> function nr_scan_try_batch() and document it. No behavior change.
>
> CC: Nick Piggin <npiggin@...e.de>
> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> CC: Christoph Lameter <cl@...ux-foundation.org>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> include/linux/mmzone.h | 4 ++--
> mm/page_alloc.c | 2 +-
> mm/vmscan.c | 39 ++++++++++++++++++++++++++++-----------
> mm/vmstat.c | 8 ++++----
> 4 files changed, 35 insertions(+), 18 deletions(-)
>
> --- mm.orig/include/linux/mmzone.h
> +++ mm/include/linux/mmzone.h
> @@ -323,9 +323,9 @@ struct zone {
>
> /* Fields commonly accessed by the page reclaim scanner */
> spinlock_t lru_lock;
> - struct {
> + struct zone_lru {
> struct list_head list;
> - unsigned long nr_scan;
> + unsigned long nr_saved_scan; /* accumulated for batching */
> } lru[NR_LRU_LISTS];
>
> struct zone_reclaim_stat reclaim_stat;
> --- mm.orig/mm/vmscan.c
> +++ mm/mm/vmscan.c
> @@ -1450,6 +1450,26 @@ static void get_scan_ratio(struct zone *
> percent[1] = 100 - percent[0];
> }
>
> +/*
> + * Smallish @nr_to_scan's are deposited in @nr_saved_scan,
> + * until we collected @swap_cluster_max pages to scan.
> + */
> +static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
> + unsigned long *nr_saved_scan,
> + unsigned long swap_cluster_max)
> +{
> + unsigned long nr;
> +
> + *nr_saved_scan += nr_to_scan;
> + nr = *nr_saved_scan;
> +
> + if (nr >= swap_cluster_max)
> + *nr_saved_scan = 0;
> + else
> + nr = 0;
> +
> + return nr;
> +}
>
> /*
> * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
> @@ -1475,14 +1495,11 @@ static void shrink_zone(int priority, st
> scan >>= priority;
> scan = (scan * percent[file]) / 100;
> }
> - if (scanning_global_lru(sc)) {
> - zone->lru[l].nr_scan += scan;
> - nr[l] = zone->lru[l].nr_scan;
> - if (nr[l] >= swap_cluster_max)
> - zone->lru[l].nr_scan = 0;
> - else
> - nr[l] = 0;
> - } else
> + if (scanning_global_lru(sc))
> + nr[l] = nr_scan_try_batch(scan,
> + &zone->lru[l].nr_saved_scan,
> + swap_cluster_max);
> + else
> nr[l] = scan;
> }
>
> @@ -2079,11 +2096,11 @@ static void shrink_all_zones(unsigned lo
> l == LRU_ACTIVE_FILE))
> continue;
>
> - zone->lru[l].nr_scan += (lru_pages >> prio) + 1;
> - if (zone->lru[l].nr_scan >= nr_pages || pass > 3) {
> + zone->lru[l].nr_saved_scan += (lru_pages >> prio) + 1;
> + if (zone->lru[l].nr_saved_scan >= nr_pages || pass > 3) {
> unsigned long nr_to_scan;
>
> - zone->lru[l].nr_scan = 0;
> + zone->lru[l].nr_saved_scan = 0;
> nr_to_scan = min(nr_pages, lru_pages);
> nr_reclaimed += shrink_list(l, nr_to_scan, zone,
> sc, prio);
> --- mm.orig/mm/vmstat.c
> +++ mm/mm/vmstat.c
> @@ -729,10 +729,10 @@ static void zoneinfo_show_print(struct s
> zone->pages_low,
> zone->pages_high,
> zone->pages_scanned,
> - zone->lru[LRU_ACTIVE_ANON].nr_scan,
> - zone->lru[LRU_INACTIVE_ANON].nr_scan,
> - zone->lru[LRU_ACTIVE_FILE].nr_scan,
> - zone->lru[LRU_INACTIVE_FILE].nr_scan,
> + zone->lru[LRU_ACTIVE_ANON].nr_saved_scan,
> + zone->lru[LRU_INACTIVE_ANON].nr_saved_scan,
> + zone->lru[LRU_ACTIVE_FILE].nr_saved_scan,
> + zone->lru[LRU_INACTIVE_FILE].nr_saved_scan,
> zone->spanned_pages,
> zone->present_pages);
>
> --- mm.orig/mm/page_alloc.c
> +++ mm/mm/page_alloc.c
> @@ -3544,7 +3544,7 @@ static void __paginginit free_area_init_
> zone_pcp_init(zone);
> for_each_lru(l) {
> INIT_LIST_HEAD(&zone->lru[l].list);
> - zone->lru[l].nr_scan = 0;
> + zone->lru[l].nr_saved_scan = 0;
> }
> zone->reclaim_stat.recent_rotated[0] = 0;
> zone->reclaim_stat.recent_rotated[1] = 0;
--
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