[PATCH] zsmalloc: consider ZS_ALMOST_FULL as migrate source

[Minchan Kim <minchan@kernel.org>]

There is no reason to prevent select ZS_ALMOST_FULL as migration
source if we cannot find source from ZS_ALMOST_EMPTY.

With this patch, zs_can_compact will return more exact result.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/zsmalloc.c |   19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 8c78bcb..7bd7dde 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1687,12 +1687,20 @@ static enum fullness_group putback_zspage(struct zs_pool *pool,
 static struct page *isolate_source_page(struct size_class *class)
 {
 	struct page *page;
+	int i;
+	bool found = false;
 
-	page = class->fullness_list[ZS_ALMOST_EMPTY];
-	if (page)
-		remove_zspage(page, class, ZS_ALMOST_EMPTY);
+	for (i = ZS_ALMOST_EMPTY; i >= ZS_ALMOST_FULL; i--) {
+		page = class->fullness_list[i];
+		if (!page)
+			continue;
 
-	return page;
+		remove_zspage(page, class, i);
+		found = true;
+		break;
+	}
+
+	return found ? page : NULL;
 }
 
 /*
@@ -1706,9 +1714,6 @@ static unsigned long zs_can_compact(struct size_class *class)
 {
 	unsigned long obj_wasted;
 
-	if (!zs_stat_get(class, CLASS_ALMOST_EMPTY))
-		return 0;
-
 	obj_wasted = zs_stat_get(class, OBJ_ALLOCATED) -
 		zs_stat_get(class, OBJ_USED);
 
-- 
1.7.9.5

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