mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request

Freepage on ZONE_HIGHMEM doesn't work for kernel memory so it's not that
important to reserve.  When ZONE_MOVABLE is used, this problem would
theorectically cause to decrease usable memory for GFP_HIGHUSER_MOVABLE
allocation request which is mainly used for page cache and anon page
allocation.  So, fix it by setting 0 to
sysctl_lowmem_reserve_ratio[ZONE_HIGHMEM].

And, defining sysctl_lowmem_reserve_ratio array by MAX_NR_ZONES - 1 size
makes code complex.  For example, if there is highmem system, following
reserve ratio is activated for *NORMAL ZONE* which would be easyily
misleading people.

 #ifdef CONFIG_HIGHMEM
 32
 #endif

This patch also fixes this situation by defining
sysctl_lowmem_reserve_ratio array by MAX_NR_ZONES and place "#ifdef" to
right place.

Link: http://lkml.kernel.org/r/1504672525-17915-1-git-send-email-iamjoonsoo.kim@lge.com
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Tony Lindgren <tony@atomide.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Laura Abbott <lauraa@codeaurora.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Cc: <linux-api@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 17 insertions, 15 deletions

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index ff234d229cbb..17256f2ad919 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -312,8 +312,6 @@ The lowmem_reserve_ratio is an array. You can see them by reading this file.
 % cat /proc/sys/vm/lowmem_reserve_ratio
 256     256     32
 -
-Note: # of this elements is one fewer than number of zones. Because the highest
-      zone's value is not necessary for following calculation.
 
 But, these values are not used directly. The kernel calculates # of protection
 pages for each zones from them. These are shown as array of protection pages
@@ -364,7 +362,8 @@ As above expression, they are reciprocal number of ratio.
 pages of higher zones on the node.
 
 If you would like to protect more pages, smaller values are effective.
-The minimum value is 1 (1/1 -> 100%).
+The minimum value is 1 (1/1 -> 100%). The value less than 1 completely
+disables protection of the pages.
 
 ==============================================================
 
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index a0c9e45a859a..32699b2dc52a 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -885,7 +885,7 @@ int min_free_kbytes_sysctl_handler(struct ctl_table *, int,
                                         void __user *, size_t *, loff_t *);
 int watermark_scale_factor_sysctl_handler(struct ctl_table *, int,
                                         void __user *, size_t *, loff_t *);
-extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1];
+extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES];
 int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *, int,
                                         void __user *, size_t *, loff_t *);
 int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *, int,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b04667848375..34a4c12d2675 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -205,17 +205,18 @@ static void __free_pages_ok(struct page *page, unsigned int order);
  * TBD: should special case ZONE_DMA32 machines here - in those we normally
  * don't need any ZONE_NORMAL reservation
  */
-int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = {
+int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES] = {
 #ifdef CONFIG_ZONE_DMA
-         256,
+        [ZONE_DMA] = 256,
 #endif
 #ifdef CONFIG_ZONE_DMA32
-         256,
+        [ZONE_DMA32] = 256,
 #endif
+        [ZONE_NORMAL] = 32,
 #ifdef CONFIG_HIGHMEM
-         32,
+        [ZONE_HIGHMEM] = 0,
 #endif
-         32,
+        [ZONE_MOVABLE] = 0,
 };
 
 EXPORT_SYMBOL(totalram_pages);
@@ -7132,13 +7133,15 @@ static void setup_per_zone_lowmem_reserve(void)
                                 struct zone *lower_zone;
 
                                 idx--;
-
-                                if (sysctl_lowmem_reserve_ratio[idx] < 1)
-                                        sysctl_lowmem_reserve_ratio[idx] = 1;
-
                                 lower_zone = pgdat->node_zones + idx;
-                                lower_zone->lowmem_reserve[j] = managed_pages /
-                                        sysctl_lowmem_reserve_ratio[idx];
+
+                                if (sysctl_lowmem_reserve_ratio[idx] < 1) {
+                                        sysctl_lowmem_reserve_ratio[idx] = 0;
+                                        lower_zone->lowmem_reserve[j] = 0;
+                                } else {
+                                        lower_zone->lowmem_reserve[j] =
+                                                managed_pages / sysctl_lowmem_reserve_ratio[idx];
+                                }
                                 managed_pages += lower_zone->managed_pages;
                         }
                 }