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From: KAMEZAWA Hiroyuki on 15 Dec 2009 04:20
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com>

Final purpose of this patch is for improving oom/memoy shortage detection
better. In general there are OOM cases that lowmem is exhausted. What
this lowmem means is determined by the situation, but in general,
limited amount of memory for some special use is lowmem.

This patch adds an integer lowmem_zone, which is initialized to -1.
If zone_idx(zone) <= lowmem_zone, the zone is lowmem.

This patch uses simple definition that the zone for special use is the lowmem.
Not taking the amount of memory into account.

For example,
- if HIGHMEM is used, NORMAL is lowmem.
- If the system has both of NORMAL and DMA32, DMA32 is lowmem.
- When the system consists of only one zone, there are no lowmem.

This will be used for lowmem accounting per mm_struct and its information
will be used for oom-killer.

Q: Why you don't use policy_zone ?
A: It's for NUMA only. I want to use unified approach for detecting lowmem.
And policy_zone sounds like "for mempolicy"..

Concerns or TODO:
- Now, we have polizy_zone if CONFIG_NUMA=y. Maybe we can make it as
#define policy_zone (lowmem_zone + 1)
or remove it. But this itself should be done in other patch.

Changelog: 2009/12/14
- no change.
Changelog: 2009/12/09
- stop using policy_zone and use unified definition on each config.

Reviewed-by: Minchan Kim <minchan.kim(a)gmail.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com>
---
include/linux/mm.h | 9 +++++++
mm/page_alloc.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 71 insertions(+)

Index: mmotm-2.6.32-Dec8-pth/include/linux/mm.h
===================================================================
--- mmotm-2.6.32-Dec8-pth.orig/include/linux/mm.h
+++ mmotm-2.6.32-Dec8-pth/include/linux/mm.h
@@ -583,6 +583,15 @@ static inline void set_page_links(struct
}

/*
+ * Check a page is in lower zone
+ */
+extern int lowmem_zone;
+static inline bool is_lowmem_page(struct page *page)
+{
+ return page_zonenum(page) <= lowmem_zone;
+}
+
+/*
* Some inline functions in vmstat.h depend on page_zone()
*/
#include <linux/vmstat.h>
Index: mmotm-2.6.32-Dec8-pth/mm/page_alloc.c
===================================================================
--- mmotm-2.6.32-Dec8-pth.orig/mm/page_alloc.c
+++ mmotm-2.6.32-Dec8-pth/mm/page_alloc.c
@@ -2311,6 +2311,59 @@ static void zoneref_set_zone(struct zone
zoneref->zone_idx = zone_idx(zone);
}

+/* the zone is lowmem if zone_idx(zone) <= lowmem_zone */
+int lowmem_zone __read_mostly;
+/*
+ * Find out LOWMEM zone on this host. LOWMEM means a zone for special use
+ * and its size seems small and precious than other zones. For example,
+ * NORMAL zone is considered to be LOWMEM on a host which has HIGHMEM.
+ *
+ * This lowmem zone is determined by zone ordering and equipped memory layout.
+ * The amount of memory is not taken into account now.
+ */
+static void find_lowmem_zone(void)
+{
+ unsigned long pages[MAX_NR_ZONES];
+ struct zone *zone;
+ int idx;
+
+ for (idx = 0; idx < MAX_NR_ZONES; idx++)
+ pages[idx] = 0;
+ /* count the number of pages */
+ for_each_populated_zone(zone) {
+ idx = zone_idx(zone);
+ pages[idx] += zone->present_pages;
+ }
+ /* If We have HIGHMEM...we ignore ZONE_MOVABLE in this case. */
+#ifdef CONFIG_HIGHMEM
+ if (pages[ZONE_HIGHMEM]) {
+ lowmem_zone = ZONE_NORMAL;
+ return;
+ }
+#endif
+ /* If We have MOVABLE zone...which works like HIGHMEM. */
+ if (pages[ZONE_MOVABLE]) {
+ lowmem_zone = ZONE_NORMAL;
+ return;
+ }
+#ifdef CONFIG_ZONE_DMA32
+ /* If we have DMA32 and there is ZONE_NORMAL...*/
+ if (pages[ZONE_DMA32] && pages[ZONE_NORMAL]) {
+ lowmem_zone = ZONE_DMA32;
+ return;
+ }
+#endif
+#ifdef CONFIG_ZONE_DMA
+ /* If we have DMA and there is ZONE_NORMAL...*/
+ if (pages[ZONE_DMA] && pages[ZONE_NORMAL]) {
+ lowmem_zone = ZONE_DMA;
+ return;
+ }
+#endif
+ lowmem_zone = -1;
+ return;
+}
+
/*
* Builds allocation fallback zone lists.
*
@@ -2790,12 +2843,21 @@ void build_all_zonelists(void)
else
page_group_by_mobility_disabled = 0;

+ find_lowmem_zone();
+
printk("Built %i zonelists in %s order, mobility grouping %s. "
"Total pages: %ld\n",
nr_online_nodes,
zonelist_order_name[current_zonelist_order],
page_group_by_mobility_disabled ? "off" : "on",
vm_total_pages);
+
+ if (lowmem_zone >= 0)
+ printk("LOWMEM zone is detected as %s\n",
+ zone_names[lowmem_zone]);
+ else
+ printk("There are no special LOWMEM. The system seems flat\n");
+
#ifdef CONFIG_NUMA
printk("Policy zone: %s\n", zone_names[policy_zone]);
#endif

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