Re: [RFC][PATCH 8/8] RSS controller support reclamation

[Pavel Emelianov <xemul@openvz.org>]

Balbir Singh wrote:
> Reclaim memory as we hit the max_shares limit. The code for reclamation
> is inspired from Dave Hansen's challenged memory controller and from the
> shrink_all_memory() code
> 
> Reclamation can be triggered from two paths
> 
> 1. While incrementing the RSS, we hit the limit of the container
> 2. A container is resized, such that it's new limit is below its current
>    RSS
> 
> In (1) reclamation takes place in the background.

Hmm... This is not a hard limit in this case, right? And in case
of overloaded system from the moment reclamation thread is woken
up till the moment it starts shrinking zones container may touch
too many pages...

That's not good.

> TODO's
> 
> 1. max_shares currently works like a soft limit. The RSS can grow beyond it's
>    limit. One possible fix is to introduce a soft limit (reclaim when the
>    container hits the soft limit) and fail when we hit the hard limit

Such soft limit doesn't help also. It just makes effects on
low-loaded system smoother.

And what about a hard limit - how would you fail in page fault in
case of limit hit? SIGKILL/SEGV is not an option - in this case we
should run synchronous reclamation. This is done in beancounter
patches v6 we've sent recently.

> Signed-off-by: Balbir Singh <balbir@in.ibm.com>
> ---
> 
> --- linux-2.6.19-rc2/mm/vmscan.c~container-memctlr-reclaim	2006-11-09 22:21:11.000000000 +0530
> +++ linux-2.6.19-rc2-balbir/mm/vmscan.c	2006-11-09 22:21:11.000000000 +0530
> @@ -36,6 +36,8 @@
>  #include <linux/rwsem.h>
>  #include <linux/delay.h>
>  #include <linux/kthread.h>
> +#include <linux/container.h>
> +#include <linux/memctlr.h>
>  
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -65,6 +67,9 @@ struct scan_control {
>  	int swappiness;
>  
>  	int all_unreclaimable;
> +
> +	int overlimit;
> +	void *container;	/* Added as void * to avoid #ifdef's */
>  };
>  
>  /*
> @@ -811,6 +816,10 @@ force_reclaim_mapped:
>  		cond_resched();
>  		page = lru_to_page(&l_hold);
>  		list_del(&page->lru);
> +		if (!memctlr_page_reclaim(page, sc->container, sc->overlimit)) {
> +			list_add(&page->lru, &l_active);
> +			continue;
> +		}
>  		if (page_mapped(page)) {
>  			if (!reclaim_mapped ||
>  			    (total_swap_pages == 0 && PageAnon(page)) ||

[snip] See comment below.

>  
> +#ifdef CONFIG_RES_GROUPS_MEMORY
> +/*
> + * Modelled after shrink_all_memory
> + */
> +unsigned long memctlr_shrink_container_memory(unsigned long nr_pages,
> +						struct container *container,
> +						int overlimit)
> +{
> +	unsigned long lru_pages;
> +	unsigned long ret = 0;
> +	int pass;
> +	struct zone *zone;
> +	struct scan_control sc = {
> +		.gfp_mask = GFP_KERNEL,
> +		.may_swap = 0,
> +		.swap_cluster_max = nr_pages,
> +		.may_writepage = 1,
> +		.swappiness = vm_swappiness,
> +		.overlimit = overlimit,
> +		.container = container,
> +	};
> +

[snip]

> +		for (prio = DEF_PRIORITY; prio >= 0; prio--) {
> +			unsigned long nr_to_scan = nr_pages - ret;
> +
> +			sc.nr_scanned = 0;
> +			ret += shrink_all_zones(nr_to_scan, prio, pass, &sc);
> +			if (ret >= nr_pages)
> +				break;
> +
> +			if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
> +				blk_congestion_wait(WRITE, HZ / 10);
> +		}
> +	}
> +	return ret;
> +}
> +#endif

Please correct me if I'm wrong, but does this reclamation work like
"run over all the zones' lists searching for page whose controller
is sc->container" ?

[snip]

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