[PATCH] mm/vmpressure: scale window size based on machine memory and CPU count

[Benjamin Lee McQueen <mcq@disroot.org>]

the vmpressure window size was recently fixed at 512 pages regardless
of machine size, this patch makes it scale based on the machine memory
and CPU count.

Signed-off-by: Benjamin Lee McQueen <mcq@disroot.org>
---
 mm/vmpressure.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 3fbb86996c4d..b2989c70dd39 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -32,10 +32,20 @@
  * As the vmscan reclaimer logic works with chunks which are multiple of
  * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
  *
- * TODO: Make the window size depend on machine size, as we do for vmstat
- * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
+ * Window size is now scaled based on RAM and CPU size, similarly to how
+ * vmstat checks them.
  */
-static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
+static unsigned long vmpressure_win;
+
+static int __init vmpressure_win_init(void)
+{
+        unsigned long mem = totalram_pages() >> (27 - PAGE_SHIFT);
+
+	vmpressure_win = SWAP_CLUSTER_MAX * max(16UL,
+		2UL * fls(num_online_cpus()) * (1 + fls(mem)));
+        return 0;
+}
+core_initcall(vmpressure_win_init);
 
 /*
  * These thresholds are used when we account memory pressure through
-- 
2.53.0