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.senozhat...@gmail.com>
---
 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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