zsmalloc: partial page ordering within a fullness_list

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@kernel.org: code adjustments]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 5 deletions

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 27b9661c8fa6..615b9b9b45eb 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -643,13 +643,22 @@ 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;
 }
 
 /*