mm: vmpressure: scale pressure based on reclaim context

The existing calculation of vmpressure takes into account only
the ratio of reclaimed to scanned pages, but not the time spent
or the difficulty in reclaiming those pages. For e.g. when there
are quite a number of file pages in the system, an allocation
request can be satisfied by reclaiming the file pages alone. If
such a reclaim is successful, the vmpressure value will remain low
irrespective of the time spent by the reclaim code to free up the
file pages. With a feature like lowmemorykiller, killing a task
can be faster than reclaiming the file pages alone. So if the
vmpressure values reflect the reclaim difficulty level, clients
can make a decision based on that, for e.g. to kill a task early.

This patch monitors the number of pages scanned in the direct
reclaim path and scales the vmpressure level according to that.

Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
Change-Id: I6e643d29a9a1aa0814309253a8b690ad86ec0b13

mm/vmpressure.c

@@ -441,6 +441,7 @@ static void vmpressure_global(gfp_t gfp, unsigned long scanned,
 {
 	struct vmpressure *vmpr = &global_vmpressure;
 	unsigned long pressure;
+	unsigned long stall;
 
 	if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
 		return;
@@ -451,6 +452,11 @@ static void vmpressure_global(gfp_t gfp, unsigned long scanned,
 	spin_lock(&vmpr->sr_lock);
 	vmpr->scanned += scanned;
 	vmpr->reclaimed += reclaimed;
+
+	if (!current_is_kswapd())
+		vmpr->stall += scanned;
+
+	stall = vmpr->stall;
 	scanned = vmpr->scanned;
 	reclaimed = vmpr->reclaimed;
 	spin_unlock(&vmpr->sr_lock);
@@ -461,9 +467,11 @@ static void vmpressure_global(gfp_t gfp, unsigned long scanned,
 	spin_lock(&vmpr->sr_lock);
 	vmpr->scanned = 0;
 	vmpr->reclaimed = 0;
+	vmpr->stall = 0;
 	spin_unlock(&vmpr->sr_lock);
 
 	pressure = vmpressure_calc_pressure(scanned, reclaimed);
+	pressure = vmpressure_account_stall(pressure, stall, scanned);
 	vmpressure_notify(pressure);
 }