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Commit 4be89a34 authored by Jianyu Zhan's avatar Jianyu Zhan Committed by Linus Torvalds
Browse files

mm/vmscan.c: use DIV_ROUND_UP for calculation of zone's balance_gap and correct comments. 



Currently, we use (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1)
/ KSWAPD_ZONE_BALANCE_GAP_RATIO to avoid a zero gap value.  It's better to
use DIV_ROUND_UP macro for neater code and clear meaning.

Besides, the gap value is calculated against the per-zone "managed pages",
not "present pages".  This patch also corrects the comment and do some
rephrasing.

Signed-off-by: default avatarJianyu Zhan <nasa4836@gmail.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarRafael Aquini <aquini@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b7596fb4

include/linux/swap.h

+4 −4
Original line number Diff line number Diff line
@@ -166,10 +166,10 @@ enum { 
#define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX



/*

 * Ratio between the present memory in the zone and the "gap" that

 * we're allowing kswapd to shrink in addition to the per-zone high

 * wmark, even for zones that already have the high wmark satisfied,

 * in order to provide better per-zone lru behavior. We are ok to

 * Ratio between zone->managed_pages and the "gap" that above the per-zone

 * "high_wmark". While balancing nodes, We allow kswapd to shrink zones that

 * do not meet the (high_wmark + gap) watermark, even which already met the

 * high_wmark, in order to provide better per-zone lru behavior. We are ok to

 * spend not more than 1% of the memory for this zone balancing "gap".

 */

#define KSWAPD_ZONE_BALANCE_GAP_RATIO 100

mm/vmscan.c

+4 −6
Original line number Diff line number Diff line
@@ -2295,9 +2295,8 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc) 
	 * there is a buffer of free pages available to give compaction

	 * a reasonable chance of completing and allocating the page

	 */

	balance_gap = min(low_wmark_pages(zone),

		(zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /

			KSWAPD_ZONE_BALANCE_GAP_RATIO);

	balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP(

			zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO));

	watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);

	watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
@@ -2949,9 +2948,8 @@ static bool kswapd_shrink_zone(struct zone *zone, 
	 * high wmark plus a "gap" where the gap is either the low

	 * watermark or 1% of the zone, whichever is smaller.

	 */

	balance_gap = min(low_wmark_pages(zone),

		(zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /

		KSWAPD_ZONE_BALANCE_GAP_RATIO);

	balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP(

			zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO));



	/*

	 * If there is no low memory pressure or the zone is balanced then no