mm/thp: don't count ZONE_MOVABLE as the target for freepage reserving

There was a regression report for "mm/cma: manage the memory of the CMA
area by using the ZONE_MOVABLE" [1] and I think that it is related to
this problem.  CMA patchset makes the system use one more zone
(ZONE_MOVABLE) and then increases min_free_kbytes.  It reduces usable
memory and it could cause regression.

ZONE_MOVABLE only has movable pages so we don't need to keep enough
freepages to avoid or deal with fragmentation.  So, don't count it.

This changes min_free_kbytes and thus min_watermark greatly if
ZONE_MOVABLE is used.  It will make the user uses more memory.

System:
  22GB ram, fakenuma, 2 nodes. 5 zones are used.

Before:
  min_free_kbytes: 112640

  zone_info (min_watermark):
  Node 0, zone      DMA
          min      19
  Node 0, zone    DMA32
          min      3778
  Node 0, zone   Normal
          min      10191
  Node 0, zone  Movable
          min      0
  Node 0, zone   Device
          min      0
  Node 1, zone      DMA
          min      0
  Node 1, zone    DMA32
          min      0
  Node 1, zone   Normal
          min      14043
  Node 1, zone  Movable
          min      127
  Node 1, zone   Device
          min      0

After:
  min_free_kbytes: 90112

  zone_info (min_watermark):
  Node 0, zone      DMA
          min      15
  Node 0, zone    DMA32
          min      3022
  Node 0, zone   Normal
          min      8152
  Node 0, zone  Movable
          min      0
  Node 0, zone   Device
          min      0
  Node 1, zone      DMA
          min      0
  Node 1, zone    DMA32
          min      0
  Node 1, zone   Normal
          min      11234
  Node 1, zone  Movable
          min      102
  Node 1, zone   Device
          min      0

[1] (lkml.kernel.org/r/20180102063528.GG30397%20()%20yexl-desktop)

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Joonsoo Kim <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: "Kirill A . Shutemov" <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index c15da1ea7e639bc0ab56bc747a4f7110c38f7187..eb32d0707c80d554c040cd0ea350913b31888429 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1879,8 +1879,16 @@ static void set_recommended_min_free_kbytes(void)
        int nr_zones = 0;
        unsigned long recommended_min;
 
-       for_each_populated_zone(zone)
+       for_each_populated_zone(zone) {
+               /*
+                * We don't need to worry about fragmentation of
+                * ZONE_MOVABLE since it only has movable pages.
+                */
+               if (zone_idx(zone) > gfp_zone(GFP_USER))
+                       continue;
+
                nr_zones++;
+       }
 
        /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
        recommended_min = pageblock_nr_pages * nr_zones * 2;