Re: [PATCH 04/25] mm, vmscan: Begin reclaiming pages on a per-node basis

["Hillf Danton" <hillf.zj@alibaba-inc.com>]

> @@ -1319,6 +1322,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  	struct list_head *src = &lruvec->lists[lru];
>  	unsigned long nr_taken = 0;
>  	unsigned long scan;
> +	LIST_HEAD(pages_skipped);
> 
>  	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
>  		struct page *page;
> @@ -1329,6 +1333,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> 
>  		VM_BUG_ON_PAGE(!PageLRU(page), page);
> 
> +		if (page_zone_id(page) > sc->reclaim_idx)
> +			list_move(&page->lru, &pages_skipped);
> +
>  		switch (__isolate_lru_page(page, mode)) {
>  		case 0:
>  			nr_pages = hpage_nr_pages(page);
> @@ -1347,6 +1354,15 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  		}
>  	}
> 
> +	/*
> +	 * Splice any skipped pages to the start of the LRU list. Note that
> +	 * this disrupts the LRU order when reclaiming for lower zones but
> +	 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
> +	 * scanning would soon rescan the same pages to skip and put the
> +	 * system at risk of premature OOM.
> +	 */
> +	if (!list_empty(&pages_skipped))
> +		list_splice(&pages_skipped, src);
>  	*nr_scanned = scan;
>  	trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
>  				    nr_taken, mode, is_file_lru(lru));

Can we avoid splicing pages by skipping pages with scan not incremented?

Hillf