[FIX][PATCH 0/3] memcg: 3 fixes for memory cgroup's memory reclaim

[FIX][PATCH 0/3] memcg: 3 fixes for memory cgroup's memory reclaim

[KAMEZAWA Hiroyuki]

This series contains 3 fixes for memcg in Linus's git tree.
All of them were posted in the last week. I cut out and refreshed
and post it here because I think all pathces has obvious benfits, I think.

All of patches are independent from each other but you may see
some dependency between 1 and 2.

1/3 .... fix memory cgroup reclaimable check.
2/3 .... fix memory cgroup numascan update by events
3/3 .... fix lock_page() trouble when using memcg.

Because 3/3 is a patch to change behavior of __do_fault(), I'd like
to get review of mm specialists.

Thanks,
-Kame

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[PATCH 1/3] memcg: fix reclaimable lru check in memcg.

[KAMEZAWA Hiroyuki]

[FIX][PATCH 2/3] memcg: fix numa scan information update to be triggered by memory event

[KAMEZAWA Hiroyuki]

[PATCH 3/3] mm: preallocate page before lock_page() at filemap COW

[KAMEZAWA Hiroyuki]

Re: [FIX][PATCH 2/3] memcg: fix numa scan information update to be triggered by memory event

[Michal Hocko]

On Tue 28-06-11 17:41:50, KAMEZAWA Hiroyuki wrote:
> From 646ca5cd1e1ab0633892b86a1bbb6cf600d79d58 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date: Tue, 28 Jun 2011 17:09:25 +0900
> Subject: [PATCH 2/3] Fix numa scan information update to be triggered by memory event
> 
> commit 889976 adds an numa node round-robin for memcg. But the information
> is updated once per 10sec.
> 
> This patch changes the update trigger from jiffies to memcg's event count.
> After this patch, numa scan information will be updated when we see
> 1024 events of pagein/pageout under a memcg.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Reviewed-by: Michal Hocko <mhocko@suse.cz>

See the note about wasted memory for MAX_NUMNODES==1 bellow.

> 
> Changelog:
>   - simplified
>   - removed mutex
>   - removed 3% check. To use heuristics, we cannot avoid magic value.
>     So, removed heuristics.
> ---
>  mm/memcontrol.c |   29 +++++++++++++++++++++++++----
>  1 files changed, 25 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index c624312..3e7d5e6 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -108,10 +108,12 @@ enum mem_cgroup_events_index {
>  enum mem_cgroup_events_target {
>  	MEM_CGROUP_TARGET_THRESH,
>  	MEM_CGROUP_TARGET_SOFTLIMIT,
> +	MEM_CGROUP_TARGET_NUMAINFO,

This still wastes sizeof(unsigned long) per CPU space for non NUMA
machines (resp. MAX_NUMNODES==1).

[...]
> @@ -703,6 +709,14 @@ static void memcg_check_events(struct mem_cgroup *mem, struct page *page)
>  			__mem_cgroup_target_update(mem,
>  				MEM_CGROUP_TARGET_SOFTLIMIT);
>  		}
> +#if MAX_NUMNODES > 1
> +		if (unlikely(__memcg_event_check(mem,
> +			MEM_CGROUP_TARGET_NUMAINFO))) {
> +			atomic_inc(&mem->numainfo_events);
> +			__mem_cgroup_target_update(mem,
> +				MEM_CGROUP_TARGET_NUMAINFO);
> +		}
> +#endif
>  	}
>  }
>  
> @@ -1582,11 +1596,15 @@ static bool test_mem_cgroup_node_reclaimable(struct mem_cgroup *mem,
>  static void mem_cgroup_may_update_nodemask(struct mem_cgroup *mem)
>  {
>  	int nid;
> -
> -	if (time_after(mem->next_scan_node_update, jiffies))
> +	/*
> +	 * numainfo_events > 0 means there was at least NUMAINFO_EVENTS_TARGET
> +	 * pagein/pageout changes since the last update.
> +	 */
> +	if (!atomic_read(&mem->numainfo_events))
> +		return;

At first I was worried about memory barriers here because
atomic_{set,inc} used for numainfo_events do not imply mem. barriers
but that is not a problem because memcg_check_events will always make
numainfo_events > 0 (even if it doesn't see atomic_set from this
function and we are not interested in the exact value).

> +	if (atomic_inc_return(&mem->numainfo_updating) > 1)
>  		return;

OK, this one should be barrier safe as well as this enforces barrier on
both sides (before and after operation) so the atomic_set shouldn't
break it AFAIU.

>  
> -	mem->next_scan_node_update = jiffies + 10*HZ;
>  	/* make a nodemask where this memcg uses memory from */
>  	mem->scan_nodes = node_states[N_HIGH_MEMORY];
>  
> @@ -1595,6 +1613,9 @@ static void mem_cgroup_may_update_nodemask(struct mem_cgroup *mem)
>  		if (!test_mem_cgroup_node_reclaimable(mem, nid, false))
>  			node_clear(nid, mem->scan_nodes);
>  	}
> +
> +	atomic_set(&mem->numainfo_events, 0);
> +	atomic_set(&mem->numainfo_updating, 0);
>  }
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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Re: [PATCH 1/3] memcg: fix reclaimable lru check in memcg.

[Michal Hocko]

On Tue 28-06-11 17:39:58, KAMEZAWA Hiroyuki wrote:
> From b52bcd09843e903e5f184d0ee499909d072f3c8d Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date: Tue, 28 Jun 2011 15:45:38 +0900
> Subject: [PATCH 1/3] memcg: fix reclaimable lru check in memcg.
> 
> Now, in mem_cgroup_hierarchical_reclaim(), mem_cgroup_local_usage()
> is used for checking whether the memcg contains reclaimable pages
> or not. If no pages in it, the routine skips it.
> 
> But, mem_cgroup_local_usage() contains Unevictable pages and cannot
> handle "noswap" condition correctly. This doesn't work on a swapless
> system.
> 
> This patch adds test_mem_cgroup_reclaimable() and replaces
> mem_cgroup_local_usage(). test_mem_cgroup_reclaimable() see LRU
> counter and returns correct answer to the caller.
> And this new function has "noswap" argument and can see only
> FILE LRU if necessary.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Reviewed-by: Michal Hocko <mhocko@suse.cz>

except for !CONFIG_NUMA issue - see bellow.

> @@ -1559,6 +1550,27 @@ mem_cgroup_select_victim(struct mem_cgroup *root_mem)
>  	return ret;
>  }
>  
> +/** test_mem_cgroup_node_reclaimable
> + * @mem: the target memcg
> + * @nid: the node ID to be checked.
> + * @noswap : specify true here if the user wants flle only information.
> + *
> + * This function returns whether the specified memcg contains any
> + * reclaimable pages on a node. Returns true if there are any reclaimable
> + * pages in the node.
> + */
> +static bool test_mem_cgroup_node_reclaimable(struct mem_cgroup *mem,
> +		int nid, bool noswap)
> +{
> +	if (mem_cgroup_node_nr_file_lru_pages(mem, nid))
> +		return true;

I do not see definition of mem_cgroup_node_nr_file_lru_pages for
!MAX_NUMNODES==1 (resp. !CONFIG_NUMA) and you are calling this function
also from that context.

>  #if MAX_NUMNODES > 1
>  
>  /*
> @@ -1580,15 +1592,8 @@ static void mem_cgroup_may_update_nodemask(struct mem_cgroup *mem)
>  
>  	for_each_node_mask(nid, node_states[N_HIGH_MEMORY]) {
>  
> -		if (mem_cgroup_get_zonestat_node(mem, nid, LRU_INACTIVE_FILE) ||
> -		    mem_cgroup_get_zonestat_node(mem, nid, LRU_ACTIVE_FILE))
> -			continue;
> -
> -		if (total_swap_pages &&
> -		    (mem_cgroup_get_zonestat_node(mem, nid, LRU_INACTIVE_ANON) ||
> -		     mem_cgroup_get_zonestat_node(mem, nid, LRU_ACTIVE_ANON)))
> -			continue;
> -		node_clear(nid, mem->scan_nodes);
> +		if (!test_mem_cgroup_node_reclaimable(mem, nid, false))
> +			node_clear(nid, mem->scan_nodes);

Nice clean up.

> @@ -1627,11 +1632,51 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *mem)
>  	return node;
>  }
>  
> +/*
> + * Check all nodes whether it contains reclaimable pages or not.
> + * For quick scan, we make use of scan_nodes. This will allow us to skip
> + * unused nodes. But scan_nodes is lazily updated and may not cotain
> + * enough new information. We need to do double check.
> + */
> +bool mem_cgroup_reclaimable(struct mem_cgroup *mem, bool noswap)
> +{
> +	int nid;
> +
> +	/*
> +	 * quick check...making use of scan_node.
> +	 * We can skip unused nodes.
> +	 */
> +	if (!nodes_empty(mem->scan_nodes)) {
> +		for (nid = first_node(mem->scan_nodes);
> +		     nid < MAX_NUMNODES;
> +		     nid = next_node(nid, mem->scan_nodes)) {
> +
> +			if (test_mem_cgroup_node_reclaimable(mem, nid, noswap))
> +				return true;
> +		}
> +	}
> +	/*
> + 	 * Check rest of nodes.
> + 	 */
> +	for_each_node_state(nid, N_HIGH_MEMORY) {
> +		if (node_isset(nid, mem->scan_nodes))
> +			continue;
> +		if (test_mem_cgroup_node_reclaimable(mem, nid, noswap))
> +			return true;	
> +	}
> +	return false;
> +}
> +
>  #else

This is #else if MAX_NUMNODES == 1 AFAICS

>  int mem_cgroup_select_victim_node(struct mem_cgroup *mem)
>  {
>  	return 0;
>  }
> +
> +bool mem_cgroup_reclaimable(struct mem_cgroup *mem, bool noswap)
> +{
> +	return test_mem_cgroup_node_reclaimable(mem, 0, noswap);
> +}
>  #endif

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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