[PATCH] Make high and batch sizes of per_cpu_pagelists configurable

As recently there has been lot of traffic on the right values for batch and
high water marks for per_cpu_pagelists.  This patch makes these two
variables configurable through /proc interface.

A new tunable /proc/sys/vm/percpu_pagelist_fraction is added.  This entry
controls the fraction of pages at most in each zone that are allocated for
each per cpu page list.  The min value for this is 8.  It means that we
don't allow more than 1/8th of pages in each zone to be allocated in any
single per_cpu_pagelist.

The batch value of each per cpu pagelist is also updated as a result.  It
is set to pcp->high/4.  The upper limit of batch is (PAGE_SHIFT * 8)

Signed-off-by: Rohit Seth <rohit.seth@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 49 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5eeeadd9f66a..2c46f697e8ff 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -53,6 +53,7 @@ struct pglist_data *pgdat_list __read_mostly;
 unsigned long totalram_pages __read_mostly;
 unsigned long totalhigh_pages __read_mostly;
 long nr_swap_pages;
+int percpu_pagelist_fraction;
 
 static void fastcall free_hot_cold_page(struct page *page, int cold);
 
@@ -1831,6 +1832,24 @@ inline void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
         INIT_LIST_HEAD(&pcp->list);
 }
 
+/*
+ * setup_pagelist_highmark() sets the high water mark for hot per_cpu_pagelist
+ * to the value high for the pageset p.
+ */
+
+static void setup_pagelist_highmark(struct per_cpu_pageset *p,
+                                unsigned long high)
+{
+        struct per_cpu_pages *pcp;
+
+        pcp = &p->pcp[0]; /* hot list */
+        pcp->high = high;
+        pcp->batch = max(1UL, high/4);
+        if ((high/4) > (PAGE_SHIFT * 8))
+                pcp->batch = PAGE_SHIFT * 8;
+}
+
+
 #ifdef CONFIG_NUMA
 /*
  * Boot pageset table. One per cpu which is going to be used for all
@@ -1868,6 +1887,10 @@ static int __devinit process_zones(int cpu)
                         goto bad;
 
                 setup_pageset(zone->pageset[cpu], zone_batchsize(zone));
+
+                if (percpu_pagelist_fraction)
+                        setup_pagelist_highmark(zone_pcp(zone, cpu),
+                                (zone->present_pages / percpu_pagelist_fraction));
         }
 
         return 0;
@@ -2567,6 +2590,32 @@ int lowmem_reserve_ratio_sysctl_handler(ctl_table *table, int write,
         return 0;
 }
 
+/*
+ * percpu_pagelist_fraction - changes the pcp->high for each zone on each
+ * cpu.  It is the fraction of total pages in each zone that a hot per cpu pagelist
+ * can have before it gets flushed back to buddy allocator.
+ */
+
+int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write,
+        struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
+{
+        struct zone *zone;
+        unsigned int cpu;
+        int ret;
+
+        ret = proc_dointvec_minmax(table, write, file, buffer, length, ppos);
+        if (!write || (ret == -EINVAL))
+                return ret;
+        for_each_zone(zone) {
+                for_each_online_cpu(cpu) {
+                        unsigned long  high;
+                        high = zone->present_pages / percpu_pagelist_fraction;
+                        setup_pagelist_highmark(zone_pcp(zone, cpu), high);
+                }
+        }
+        return 0;
+}
+
 __initdata int hashdist = HASHDIST_DEFAULT;
 
 #ifdef CONFIG_NUMA