Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis

[Mel Gorman]

On Mon, Jul 18, 2016 at 01:11:22PM +0100, Mel Gorman wrote:
> The all_unreclaimable logic is related to the number of pages scanned
> but currently pages skipped contributes to pages scanned. That is one
> possibility. The other is that if all pages scanned are skipped then the
> OOM killer can believe there is zero progress.
> 
> Try this to start with;
> 

And if that fails, try this heavier handed version that will scan the full
LRU potentially to isolate at least a single page if it's available for
zone-constrained allocations. It's compile-tested only

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a6f31617a08c..6a35691c8b94 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1408,14 +1408,14 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		isolate_mode_t mode, enum lru_list lru)
 {
 	struct list_head *src = &lruvec->lists[lru];
-	unsigned long nr_taken = 0;
+	unsigned long nr_taken = 0, total_skipped = 0;
 	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
 	unsigned long nr_skipped[MAX_NR_ZONES] = { 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); scan++) {
+			!list_empty(src) && scan == total_skipped; scan++) {
 		struct page *page;
 
 		page = lru_to_page(src);
@@ -1426,6 +1426,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		if (page_zonenum(page) > sc->reclaim_idx) {
 			list_move(&page->lru, &pages_skipped);
 			nr_skipped[page_zonenum(page)]++;
+			total_skipped++;
 			continue;
 		}
 
@@ -1465,7 +1466,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
 		}
 	}
-	*nr_scanned = scan;
+	*nr_scanned = scan - total_skipped;
 	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, scan,
 				    nr_taken, mode, is_file_lru(lru));
 	update_lru_sizes(lruvec, lru, nr_zone_taken, nr_taken);

-- 
Mel Gorman
SUSE Labs