Subject: remove lumpy_reclaim

From: Andrea Arcangeli <aarcange@redhat.com>

Even with memory compaction enabled, without this patch, after:

	echo always >/sys/kernel/mm/transparent_hugepage/defrag

the system becomes unusable and swaps despite gigabytes of clean cache
available in the inactive list. Any frequent high order allocation (despite
being done with noretry/nomemalloc/nowarn) grinds the system to unusable state.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -75,12 +75,6 @@ struct scan_control {
 
 	int order;
 
-	/*
-	 * Intend to reclaim enough contenious memory rather than to reclaim
-	 * enough amount memory. I.e, it's the mode for high order allocation.
-	 */
-	bool lumpy_reclaim_mode;
-
 	/* Which cgroup do we reclaim from */
 	struct mem_cgroup *mem_cgroup;
 
@@ -572,10 +566,6 @@ static enum page_references page_check_r
 	referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
 	referenced_page = TestClearPageReferenced(page);
 
-	/* Lumpy reclaim - ignore references */
-	if (sc->lumpy_reclaim_mode)
-		return PAGEREF_RECLAIM;
-
 	/*
 	 * Mlock lost the isolation race with us.  Let try_to_unmap()
 	 * move the page to the unevictable list.
@@ -1131,7 +1121,6 @@ static unsigned long shrink_inactive_lis
 			return SWAP_CLUSTER_MAX;
 	}
 
-
 	pagevec_init(&pvec, 1);
 
 	lru_add_drain();
@@ -1143,14 +1132,14 @@ static unsigned long shrink_inactive_lis
 		unsigned long nr_freed;
 		unsigned long nr_active;
 		unsigned int count[NR_LRU_LISTS] = { 0, };
-		int mode = sc->lumpy_reclaim_mode ? ISOLATE_BOTH : ISOLATE_INACTIVE;
 		unsigned long nr_anon;
 		unsigned long nr_file;
 
 		if (scanning_global_lru(sc)) {
 			nr_taken = isolate_pages_global(SWAP_CLUSTER_MAX,
 							&page_list, &nr_scan,
-							sc->order, mode,
+							sc->order,
+							ISOLATE_INACTIVE,
 							zone, 0, file);
 			zone->pages_scanned += nr_scan;
 			if (current_is_kswapd())
@@ -1162,7 +1151,8 @@ static unsigned long shrink_inactive_lis
 		} else {
 			nr_taken = mem_cgroup_isolate_pages(SWAP_CLUSTER_MAX,
 							&page_list, &nr_scan,
-							sc->order, mode,
+							sc->order,
+							    ISOLATE_INACTIVE,
 							zone, sc->mem_cgroup,
 							0, file);
 			/*
@@ -1199,27 +1189,6 @@ static unsigned long shrink_inactive_lis
 		nr_scanned += nr_scan;
 		nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
 
-		/*
-		 * If we are direct reclaiming for contiguous pages and we do
-		 * not reclaim everything in the list, try again and wait
-		 * for IO to complete. This will stall high-order allocations
-		 * but that should be acceptable to the caller
-		 */
-		if (nr_freed < nr_taken && !current_is_kswapd() &&
-		    sc->lumpy_reclaim_mode) {
-			congestion_wait(BLK_RW_ASYNC, HZ/10);
-
-			/*
-			 * The attempt at page out may have made some
-			 * of the pages active, mark them inactive again.
-			 */
-			nr_active = clear_active_flags(&page_list, count);
-			count_vm_events(PGDEACTIVATE, nr_active);
-
-			nr_freed += shrink_page_list(&page_list, sc,
-							PAGEOUT_IO_SYNC);
-		}
-
 		nr_reclaimed += nr_freed;
 
 		local_irq_disable();
@@ -1641,21 +1610,6 @@ out:
 	}
 }
 
-static void set_lumpy_reclaim_mode(int priority, struct scan_control *sc)
-{
-	/*
-	 * If we need a large contiguous chunk of memory, or have
-	 * trouble getting a small set of contiguous pages, we
-	 * will reclaim both active and inactive pages.
-	 */
-	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
-		sc->lumpy_reclaim_mode = 1;
-	else if (sc->order && priority < DEF_PRIORITY - 2)
-		sc->lumpy_reclaim_mode = 1;
-	else
-		sc->lumpy_reclaim_mode = 0;
-}
-
 /*
  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
  */
@@ -1670,8 +1624,6 @@ static void shrink_zone(int priority, st
 
 	get_scan_count(zone, sc, nr, priority);
 
-	set_lumpy_reclaim_mode(priority, sc);
-
 	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
 					nr[LRU_INACTIVE_FILE]) {
 		for_each_evictable_lru(l) {