linux-kernel - Re: [PATCH 8/9] Revert "mm, vmscan: account for skipped pages as a partial scan"

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Date:   Wed, 1 Mar 2017 16:51:38 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jia He <hejianet@...il.com>, Mel Gorman <mgorman@...e.de>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 8/9] Revert "mm, vmscan: account for skipped pages as a
 partial scan"

On Tue 28-02-17 16:40:06, Johannes Weiner wrote:
> This reverts commit d7f05528eedb047efe2288cff777676b028747b6.
> 
> Now that reclaimability of a node is no longer based on the ratio
> between pages scanned and theoretically reclaimable pages, we can
> remove accounting tricks for pages skipped due to zone constraints.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/vmscan.c | 22 ++++------------------
>  1 file changed, 4 insertions(+), 18 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 35b791a8922b..ddcff8a11c1e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1471,12 +1471,12 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  	unsigned long nr_taken = 0;
>  	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
>  	unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
> -	unsigned long skipped = 0, total_skipped = 0;
> +	unsigned long skipped = 0;
>  	unsigned long scan, nr_pages;
>  	LIST_HEAD(pages_skipped);
>  
>  	for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
> -					!list_empty(src);) {
> +					!list_empty(src); scan++) {
>  		struct page *page;
>  
>  		page = lru_to_page(src);
> @@ -1490,12 +1490,6 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  			continue;
>  		}
>  
> -		/*
> -		 * Account for scanned and skipped separetly to avoid the pgdat
> -		 * being prematurely marked unreclaimable by pgdat_reclaimable.
> -		 */
> -		scan++;
> -
>  		switch (__isolate_lru_page(page, mode)) {
>  		case 0:
>  			nr_pages = hpage_nr_pages(page);
> @@ -1524,6 +1518,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  	if (!list_empty(&pages_skipped)) {
>  		int zid;
>  
> +		list_splice(&pages_skipped, src);
>  		for (zid = 0; zid < MAX_NR_ZONES; zid++) {
>  			if (!nr_skipped[zid])
>  				continue;
> @@ -1531,17 +1526,8 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
>  			skipped += nr_skipped[zid];
>  		}
> -
> -		/*
> -		 * Account skipped pages as a partial scan as the pgdat may be
> -		 * close to unreclaimable. If the LRU list is empty, account
> -		 * skipped pages as a full scan.
> -		 */
> -		total_skipped = list_empty(src) ? skipped : skipped >> 2;
> -
> -		list_splice(&pages_skipped, src);
>  	}
> -	*nr_scanned = scan + total_skipped;
> +	*nr_scanned = scan;
>  	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
>  				    scan, skipped, nr_taken, mode, lru);
>  	update_lru_sizes(lruvec, lru, nr_zone_taken);
> -- 
> 2.11.1

-- 
Michal Hocko
SUSE Labs