[RFC PATCH 3/4] mm/vmscan: drop the combined limit gate in __node_reclaim()

[Ridong Chen <ridong.chen@linux.dev>]

From: Ridong Chen <chenridong@xiaomi.com>

__node_reclaim() only ran shrink_node() when unmapped page cache was
over min_unmapped_pages OR reclaimable slab was over min_slab_pages.

With slab and file reclaim now gated per type by sc->skip_slab_reclaim and
sc->skip_file_reclaim, this combined gate is either redundant or harmful:

 - for the NUMA node reclaim caller it is always true, since
   node_reclaim() only calls in when at least one limit is exceeded;

 - for the per-node proactive reclaim caller (which does not go through
   node_reclaim()'s checks) it wrongly suppressed all reclaim -- anon
   included -- whenever both page cache and slab happened to sit at or
   below their limits, even with plenty of reclaimable anon present.

Drop the gate and let the per-type flags decide what to reclaim.  The
node reclaim path is unchanged; the proactive path can now reclaim anon
as requested.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
---
 mm/vmscan.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1e56973ceb73..5a3f67b3ba32 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -7906,16 +7906,16 @@ static unsigned long __node_reclaim(struct pglist_data *pgdat,
 	noreclaim_flag = memalloc_noreclaim_save();
 	set_task_reclaim_state(p, &sc->reclaim_state);
 
-	if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages ||
-	    node_page_state_pages(pgdat, NR_SLAB_RECLAIMABLE_B) > pgdat->min_slab_pages) {
-		/*
-		 * Free memory by calling shrink node with increasing
-		 * priorities until we have enough memory freed.
-		 */
-		do {
-			shrink_node(pgdat, sc);
-		} while (sc->nr_reclaimed < nr_pages && --sc->priority >= 0);
-	}
+	/*
+	 * Free memory by calling shrink node with increasing
+	 * priorities until we have enough memory freed.
+	 *
+	 * What to reclaim is gated per type by sc->skip_slab_reclaim and
+	 * sc->skip_file_reclaim.
+	 */
+	do {
+		shrink_node(pgdat, sc);
+	} while (sc->nr_reclaimed < nr_pages && --sc->priority >= 0);
 
 	set_task_reclaim_state(p, NULL);
 	memalloc_noreclaim_restore(noreclaim_flag);
-- 
2.34.1