[RFC][PATCHv3 2/7] 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 it keeps the list pages not in
any particular order, just like we do it now.

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

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
---
 mm/zsmalloc.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 7d816c2..6e2ebb6 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -659,8 +659,16 @@ static void insert_zspage(struct page *page, struct size_class *class,
 		return;
 
 	head = &class->fullness_list[fullness];
-	if (*head)
-		list_add_tail(&page->lru, &(*head)->lru);
+	if (*head) {
+		/*
+		 * We want to see more ZS_FULL pages and less almost
+		 * empty/full. Put pages with higher ->inuse first.
+		 */
+		if (page->inuse < (*head)->inuse)
+			list_add_tail(&page->lru, &(*head)->lru);
+		else
+			list_add(&page->lru, &(*head)->lru);
+	}
 
 	*head = page;
 	zs_stat_inc(class, fullness == ZS_ALMOST_EMPTY ?
-- 
2.4.4

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