Commit f6366156 authored by Baoquan He's avatar Baoquan He Committed by Linus Torvalds

mm/page_alloc.c: clear out zone->lowmem_reserve[] if the zone is empty

When requesting memory allocation from a specific zone is not satisfied,
it will fall to lower zone to try allocating memory.  In this case, lower
zone's ->lowmem_reserve[] will help protect its own memory resource.  The
higher the relevant ->lowmem_reserve[] is, the harder the upper zone can
get memory from this lower zone.

However, this protection mechanism should be applied to populated zone,
but not an empty zone. So filling ->lowmem_reserve[] for empty zone is
not necessary, and may mislead people that it's valid data in that zone.

Node 2, zone      DMA
  pages free     0
        min      0
        low      0
        high     0
        spanned  0
        present  0
        managed  0
        protection: (0, 0, 1024, 1024)
Node 2, zone    DMA32
  pages free     0
        min      0
        low      0
        high     0
        spanned  0
        present  0
        managed  0
        protection: (0, 0, 1024, 1024)
Node 2, zone   Normal
  per-node stats
      nr_inactive_anon 0
      nr_active_anon 143
      nr_inactive_file 0
      nr_active_file 0
      nr_unevictable 0
      nr_slab_reclaimable 45
      nr_slab_unreclaimable 254

Here clear out zone->lowmem_reserve[] if zone is empty.
Signed-off-by: default avatarBaoquan He <bhe@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200402140113.3696-3-bhe@redhat.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 86aaf255
...@@ -7704,8 +7704,10 @@ static void setup_per_zone_lowmem_reserve(void) ...@@ -7704,8 +7704,10 @@ static void setup_per_zone_lowmem_reserve(void)
idx--; idx--;
lower_zone = pgdat->node_zones + idx; lower_zone = pgdat->node_zones + idx;
if (!sysctl_lowmem_reserve_ratio[idx]) { if (!sysctl_lowmem_reserve_ratio[idx] ||
!zone_managed_pages(lower_zone)) {
lower_zone->lowmem_reserve[j] = 0; lower_zone->lowmem_reserve[j] = 0;
continue;
} else { } else {
lower_zone->lowmem_reserve[j] = lower_zone->lowmem_reserve[j] =
managed_pages / sysctl_lowmem_reserve_ratio[idx]; managed_pages / sysctl_lowmem_reserve_ratio[idx];
......
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