[PATCH 3/6] mm: make __node_reclaim() more flexible

[Davidlohr Bueso <dave@stgolabs.net>]

Currently __node_reclaim() is tailored to the allocator paths. With
proactive per-node reclaim it requires a bit more flexibly:

 - Deal in terms of nr_pages instead of order. Similarly this also
   applies to the respective tracing.
 - Make the caller pass an already armed scan control.
 - Return number of reclaimed pages. The caller can trivially check
   against this explicitly instead.

The current node_reclaim() interface remains the same.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
---
 include/trace/events/vmscan.h | 12 ++++-----
 mm/vmscan.c                   | 47 +++++++++++++++++++----------------
 2 files changed, 31 insertions(+), 28 deletions(-)

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index de136dbd623a..ab6ce8d8770b 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -439,25 +439,25 @@ TRACE_EVENT(mm_vmscan_lru_shrink_active,
 
 TRACE_EVENT(mm_vmscan_node_reclaim_begin,
 
-	TP_PROTO(int nid, int order, gfp_t gfp_flags),
+	TP_PROTO(int nid, unsigned long nr_pages, gfp_t gfp_flags),
 
-	TP_ARGS(nid, order, gfp_flags),
+	TP_ARGS(nid, nr_pages, gfp_flags),
 
 	TP_STRUCT__entry(
 		__field(int, nid)
-		__field(int, order)
+		__field(int, nr_pages)
 		__field(gfp_t, gfp_flags)
 	),
 
 	TP_fast_assign(
 		__entry->nid = nid;
-		__entry->order = order;
+		__entry->nr_pages = nr_pages;
 		__entry->gfp_flags = gfp_flags;
 	),
 
-	TP_printk("nid=%d order=%d gfp_flags=%s",
+	TP_printk("nid=%d nr_pages=%d gfp_flags=%s",
 		__entry->nid,
-		__entry->order,
+		__entry->nr_pages,
 		show_gfp_flags(__entry->gfp_flags))
 );
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index cb583fcbf5bf..1735c302831c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4668,36 +4668,28 @@ static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
 
 /*
  * Try to free up some pages from this node through reclaim.
+ * Returns the number of reclaimed pages.
  */
-static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
+static unsigned long __node_reclaim(struct pglist_data *pgdat,
+				    gfp_t gfp_mask, unsigned long nr_pages,
+				    struct scan_control *sc)
 {
 	/* Minimum pages needed in order to stay on node */
-	const unsigned long nr_pages = 1 << order;
 	struct task_struct *p = current;
 	unsigned int noreclaim_flag;
-	struct scan_control sc = {
-		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
-		.gfp_mask = current_gfp_context(gfp_mask),
-		.order = order,
-		.priority = NODE_RECLAIM_PRIORITY,
-		.may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
-		.may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
-		.may_swap = 1,
-		.reclaim_idx = gfp_zone(gfp_mask),
-	};
 	unsigned long pflags;
 
-	trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order,
-					   sc.gfp_mask);
+	trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, nr_pages,
+					   sc->gfp_mask);
 
 	cond_resched();
 	psi_memstall_enter(&pflags);
-	fs_reclaim_acquire(sc.gfp_mask);
+	fs_reclaim_acquire(sc->gfp_mask);
 	/*
 	 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
 	 */
 	noreclaim_flag = memalloc_noreclaim_save();
-	set_task_reclaim_state(p, &sc.reclaim_state);
+	set_task_reclaim_state(p, &sc->reclaim_state);
 
 	if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
 		/*
@@ -4705,23 +4697,34 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
 		 * priorities until we have enough memory freed.
 		 */
 		do {
-			shrink_node(pgdat, &sc);
-		} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
+			shrink_node(pgdat, sc);
+		} while (sc->nr_reclaimed < nr_pages && --sc->priority >= 0);
 	}
 
 	set_task_reclaim_state(p, NULL);
 	memalloc_noreclaim_restore(noreclaim_flag);
-	fs_reclaim_release(sc.gfp_mask);
+	fs_reclaim_release(sc->gfp_mask);
 	psi_memstall_leave(&pflags);
 
-	trace_mm_vmscan_node_reclaim_end(sc.nr_reclaimed);
+	trace_mm_vmscan_node_reclaim_end(sc->nr_reclaimed);
 
-	return sc.nr_reclaimed >= nr_pages;
+	return sc->nr_reclaimed;
 }
 
 int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
 {
 	int ret;
+	const unsigned long nr_pages = 1 << order;
+	struct scan_control sc = {
+		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
+		.gfp_mask = current_gfp_context(gfp_mask),
+		.order = order,
+		.priority = NODE_RECLAIM_PRIORITY,
+		.may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
+		.may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
+		.may_swap = 1,
+		.reclaim_idx = gfp_zone(gfp_mask),
+	};
 
 	/*
 	 * Node reclaim reclaims unmapped file backed pages and
@@ -4756,7 +4759,7 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
 	if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
 		return NODE_RECLAIM_NOSCAN;
 
-	ret = __node_reclaim(pgdat, gfp_mask, order);
+	ret = __node_reclaim(pgdat, gfp_mask, nr_pages, &sc) >= nr_pages;
 	clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
 
 	if (!ret)
-- 
2.26.2