[PATCH] zsmalloc: partial page ordering within a fullness_list

[Sergey Senozhatsky]

We want to see more ZS_FULL pages and less ZS_ALMOST_{FULL, EMPTY}
pages. Put a page with higher ->inuse count first within its
->fullness_list, which will give us better chances to fill up this
page with new objects (find_get_zspage() return ->fullness_list head
for new object allocation), so some zspages will become
ZS_ALMOST_FULL/ZS_FULL quicker.

It performs a trivial and cheap ->inuse compare which does not
slow down zsmalloc and in the worst case keeps the list pages in
no particular order.

A more expensive solution could sort fullness_list by ->inuse count.

[Minchan Kim: code adjustments]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
---
 mm/zsmalloc.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 0a7f81a..3538b8c 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -658,13 +658,22 @@ static void insert_zspage(struct page *page, struct size_class *class,
 	if (fullness >= _ZS_NR_FULLNESS_GROUPS)
 		return;
 
-	head = &class->fullness_list[fullness];
-	if (*head)
-		list_add_tail(&page->lru, &(*head)->lru);
-
-	*head = page;
 	zs_stat_inc(class, fullness == ZS_ALMOST_EMPTY ?
 			CLASS_ALMOST_EMPTY : CLASS_ALMOST_FULL, 1);
+
+	head = &class->fullness_list[fullness];
+	if (!*head) {
+		*head = page;
+		return;
+	}
+
+	/*
+	 * We want to see more ZS_FULL pages and less almost
+	 * empty/full. Put pages with higher ->inuse first.
+	 */
+	list_add_tail(&page->lru, &(*head)->lru);
+	if (page->inuse >= (*head)->inuse)
+		*head = page;
 }
 
 /*
-- 
2.5.0.rc0.3.g912bd49

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