setup_per_zone_lowmem_reserve() iterates through each zone setting
zone->lowmem_reserve[j] = 0 (where j is the zone's index) then
iterates backwards through all proceeding zones, setting
lower_zone->lowmem_reserve[j] = sum(managed pages of higher zones) /
lowmem_reserve_ratio[idx] for each (where idx is the lower zone's
index).
If the lower zone has no managed pages or its ratio is 0 then all of its
lowmem_reserve[] entries are effectively zeroed.
As these arrays are only assigned here and all lowmem_reserve[] entries
for index < this zone's index are implicitly assumed to be 0 (as these
are specifically output in show_free_areas() and zoneinfo_show_print()
for example) there is no need to additionally zero index == this zone's
index too. This patch avoids zeroing unnecessarily.
Rather than iterating through zones and setting lowmem_reserve[j] for
each lower zone this patch reverse the process and populates each zone's
lowmem_reserve[] values in ascending order.
This clarifies what is going on especially in the case of zero managed
pages or ratio which is now explicitly shown to clear these values.
Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
---
mm/page_alloc.c | 35 ++++++++++++++---------------------
1 file changed, 14 insertions(+), 21 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f91df593bf71..39f92de1228f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7862,31 +7862,24 @@ static void calculate_totalreserve_pages(void)
static void setup_per_zone_lowmem_reserve(void)
{
struct pglist_data *pgdat;
- enum zone_type j, idx;
+ enum zone_type i, j;
for_each_online_pgdat(pgdat) {
- for (j = 0; j < MAX_NR_ZONES; j++) {
- struct zone *zone = pgdat->node_zones + j;
- unsigned long managed_pages = zone_managed_pages(zone);
-
- zone->lowmem_reserve[j] = 0;
-
- idx = j;
- while (idx) {
- struct zone *lower_zone;
-
- idx--;
- lower_zone = pgdat->node_zones + idx;
-
- if (!sysctl_lowmem_reserve_ratio[idx] ||
- !zone_managed_pages(lower_zone)) {
- lower_zone->lowmem_reserve[j] = 0;
- continue;
+ for (i = 0; i < MAX_NR_ZONES - 1; i++) {
+ struct zone *zone = &pgdat->node_zones[i];
+ int ratio = sysctl_lowmem_reserve_ratio[i];
+ bool clear = !ratio || !zone_managed_pages(zone);
+ unsigned long managed_pages = 0;
+
+ for (j = i + 1; j < MAX_NR_ZONES; j++) {
+ if (clear) {
+ zone->lowmem_reserve[j] = 0;
} else {
- lower_zone->lowmem_reserve[j] =
- managed_pages / sysctl_lowmem_reserve_ratio[idx];
+ struct zone *upper_zone = &pgdat->node_zones[j];
+
+ managed_pages += zone_managed_pages(upper_zone);
+ zone->lowmem_reserve[j] = managed_pages / ratio;
}
- managed_pages += zone_managed_pages(lower_zone);
}
}
}
--
2.29.2
