Re: [PATCH] vmscan: get_scan_count selects anon pages conservative

[Rik van Riel <riel@redhat.com>]

On 03/04/2015 03:03 PM, Shaohua Li wrote:
> kswapd is a per-node based. Sometimes there is imbalance between nodes,
> node A is full of clean file pages (easy to reclaim), node B is
> full of anon pages (hard to reclaim). With memory pressure, kswapd will
> be waken up for both nodes. The kswapd of node B will try to swap, while
> we prefer reclaim pages from node A first. The real issue here is we
> don't have a mechanism to prevent memory allocation from a hard-reclaim
> node (node B here) if there is an easy-reclaim node (node A) to reclaim
> memory.
> 
> The swap can happen even with swapiness 0. Below is a simple script to
> trigger it. cpu 1 and 8 are in different node, each has 72G memory:
> truncate -s 70G img
> taskset -c 8 dd if=img of=/dev/null bs=4k
> taskset -c 1 usemem 70G

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 5e8eadd..31b03e6 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1990,7 +1990,7 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness,
>  	 * thrashing file LRU becomes infinitely more attractive than
>  	 * anon pages.  Try to detect this based on file LRU size.
>  	 */
> -	if (global_reclaim(sc)) {
> +	if (global_reclaim(sc) && sc->priority < DEF_PRIORITY - 2) {
>  		unsigned long zonefile;
>  		unsigned long zonefree;

What kernel does this apply to?

Current upstream does not seem to have the
"sc->priority < DEF_PRIORITY - 2" check, unless
I somehow managed to mess up "git clone" on several
systems.

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