Re: [RFC][PATCHv3 2/7] zsmalloc: partial page ordering within a fullness_list

Minchan Kim
2015-06-29T06:52:17Z

On Thu, Jun 18, 2015 at 08:46:39PM +0900, Sergey Senozhatsky wrote:
> 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@gmail.com>
> ---
> 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;

Why do you want to always put @page in the head?
How about this?

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index e8cb31c..1c5fde9 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -658,21 +658,25 @@ static void insert_zspage(struct page *page, struct size_class *class,
if (fullness >= _ZS_NR_FULLNESS_GROUPS)
return;

+ zs_stat_inc(class, fullness == ZS_ALMOST_EMPTY ?
+ CLASS_ALMOST_EMPTY : CLASS_ALMOST_FULL, 1);
+
head = &class->fullness_list[fullness];
- 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);
+ if (!*head) {
+ *head = page;
+ return;
}

- *head = page;
- zs_stat_inc(class, fullness == ZS_ALMOST_EMPTY ?
- CLASS_ALMOST_EMPTY : CLASS_ALMOST_FULL, 1);
+ /*
+ * 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;
}

/*
--
1.7.9.5

> zs_stat_inc(class, fullness == ZS_ALMOST_EMPTY ?
> --
> 2.4.4
>