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

[Minchan Kim <minchan@kernel.org>]

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
> 

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