From: Lorenzo Stoakes lstoakes@gmail.com
[ Upstream commit 470c61d70299b1826f56ff5fede10786798e3c14 ]
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 preceding 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.
Link: https://lkml.kernel.org/r/20201129162758.115907-1-lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes lstoakes@gmail.com Cc: Baoquan He bhe@redhat.com Cc: Michal Hocko mhocko@suse.com Cc: Nicholas Piggin npiggin@gmail.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Roman Gushchin guro@fb.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 81cc7fdc9c8f..f955610fb552 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -7788,31 +7788,24 @@ 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); } } }