mm: vmpressure: account allocstalls only on higher pressures

At present any vmpressure value is scaled up if the pages are
reclaimed through direct reclaim. This can result in false
vmpressure values. Consider a case where a device is booted up
and most of the memory is occuppied by file pages. kswapd will
make sure that high watermark is maintained. Now when a sudden
huge allocation request comes in, the system will definitely
have to get into direct reclaims. The vmpressures can be very low,
but because of allocstall accounting logic even these low values
will be scaled to values nearing 100. This can result in
unnecessary LMK kills for example. So define a tunable threshold
for vmpressure above which the allocstalls will be accounted.

CRs-fixed: 893699
Change-Id: Idd7c6724264ac89f1f68f2e9d70a32390ffca3e5
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>

1 files changed, 11 insertions, 2 deletions

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index b843993a9a7c..75b7ffe9e7a3 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -56,6 +56,11 @@ static unsigned long vmpressure_scale_max = 100;
 module_param_named(vmpressure_scale_max, vmpressure_scale_max,
 			ulong, S_IRUGO | S_IWUSR);
 
+/* vmpressure values >= this will be scaled based on allocstalls */
+static unsigned long allocstall_threshold = 70;
+module_param_named(allocstall_threshold, allocstall_threshold,
+			ulong, S_IRUGO | S_IWUSR);
+
 static struct vmpressure global_vmpressure;
 BLOCKING_NOTIFIER_HEAD(vmpressure_notifier);
 
@@ -165,8 +170,12 @@ static unsigned long vmpressure_calc_pressure(unsigned long scanned,
 static unsigned long vmpressure_account_stall(unsigned long pressure,
 				unsigned long stall, unsigned long scanned)
 {
-	unsigned long scale =
-		((vmpressure_scale_max - pressure) * stall) / scanned;
+	unsigned long scale;
+
+	if (pressure < allocstall_threshold)
+		return pressure;
+
+	scale = ((vmpressure_scale_max - pressure) * stall) / scanned;
 
 	return pressure + scale;
 }