Re: [PATCH] mm: exclude isolated non-lru pages from NR_ISOLATED_ANON or NR_ISOLATED_FILE.

[Michal Hocko]

On Wed 28-09-16 17:31:03, ming.ling wrote:
> Non-lru pages don't belong to any lru, so accounting them to
> NR_ISOLATED_ANON or NR_ISOLATED_FILE doesn't make any sense.
> It may misguide functions such as pgdat_reclaimable_pages and
> too_many_isolated.

OK, but it would be better to mention that this related to pfn based
migration (e.g. compaction). It is also highly appreciated to describe
the actual problem that you are seeing and tryin to fix. Is a reclaim
artificially throttled (hung) because of too many non LRU pages being
isolated? Is there a way to trigger that condition? So please tell us
more.
 
> This patch adds NR_ISOLATED_NONLRU to vmstat and moves isolated non-lru
> pages from NR_ISOLATED_ANON or NR_ISOLATED_FILE to NR_ISOLATED_NONLRU.
> And with non-lru pages in vmstat, it helps to optimize algorithm of
> function too_many_isolated oneday.

I am not entirely sure a new vmstat counter is really needed but I have
to admit that the role of too_many_isolated in isolate_migratepages_block
is quite unclear to me. Besides that I believe the patch is not correct
because you are checking PageLRU after those pages have already been
isolated from the LRU. For example putback_movable_pages operates on
pages which are put back to the LRU. I haven't checked others but I
suspect they would be in a similar situation.

> Signed-off-by: ming.ling <ming.ling@xxxxxxxxxxxxxx>
> ---
>  include/linux/mmzone.h |  1 +
>  mm/compaction.c        | 12 +++++++++---
>  mm/migrate.c           | 14 ++++++++++----
>  3 files changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 7f2ae99..dc0adba 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -169,6 +169,7 @@ enum node_stat_item {
>  	NR_VMSCAN_IMMEDIATE,	/* Prioritise for reclaim when writeback ends */
>  	NR_DIRTIED,		/* page dirtyings since bootup */
>  	NR_WRITTEN,		/* page writings since bootup */
> +	NR_ISOLATED_NONLRU,	/* Temporary isolated pages from non-lru */
>  	NR_VM_NODE_STAT_ITEMS
>  };
>  
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 9affb29..8da1dca 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -638,16 +638,21 @@ isolate_freepages_range(struct compact_control *cc,
>  static void acct_isolated(struct zone *zone, struct compact_control *cc)
>  {
>  	struct page *page;
> -	unsigned int count[2] = { 0, };
> +	unsigned int count[3] = { 0, };
>  
>  	if (list_empty(&cc->migratepages))
>  		return;
>  
> -	list_for_each_entry(page, &cc->migratepages, lru)
> -		count[!!page_is_file_cache(page)]++;
> +	list_for_each_entry(page, &cc->migratepages, lru) {
> +		if (PageLRU(page))
> +			count[!!page_is_file_cache(page)]++;
> +		else
> +			count[2]++;
> +	}
>  
>  	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON, count[0]);
>  	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, count[1]);
> +	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_NONLRU, count[2]);
>  }
>  
>  /* Similar to reclaim, but different enough that they don't share logic */
> @@ -659,6 +664,7 @@ static bool too_many_isolated(struct zone *zone)
>  			node_page_state(zone->zone_pgdat, NR_INACTIVE_ANON);
>  	active = node_page_state(zone->zone_pgdat, NR_ACTIVE_FILE) +
>  			node_page_state(zone->zone_pgdat, NR_ACTIVE_ANON);
> +	/* Is it necessary to add NR_ISOLATED_NONLRU?? */
>  	isolated = node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE) +
>  			node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON);
>  
> diff --git a/mm/migrate.c b/mm/migrate.c
> index f7ee04a..cd5abb2 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -168,8 +168,11 @@ void putback_movable_pages(struct list_head *l)
>  			continue;
>  		}
>  		list_del(&page->lru);
> -		dec_node_page_state(page, NR_ISOLATED_ANON +
> -				page_is_file_cache(page));
> +		if (PageLRU(page))
> +			dec_node_page_state(page, NR_ISOLATED_ANON +
> +					page_is_file_cache(page));
> +		else
> +			dec_node_page_state(page, NR_ISOLATED_NONLRU);
>  		/*
>  		 * We isolated non-lru movable page so here we can use
>  		 * __PageMovable because LRU page's mapping cannot have
> @@ -1121,8 +1124,11 @@ out:
>  		 * restored.
>  		 */
>  		list_del(&page->lru);
> -		dec_node_page_state(page, NR_ISOLATED_ANON +
> -				page_is_file_cache(page));
> +		if (PageLRU(page))
> +			dec_node_page_state(page, NR_ISOLATED_ANON +
> +					page_is_file_cache(page));
> +		else
> +			dec_node_page_state(page, NR_ISOLATED_NONLRU);
>  	}
>  
>  	/*
> -- 
> 1.9.1
> 
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-- 
Michal Hocko
SUSE Labs