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Subject[PATCH 3/3] Provide control over unmapped pages (v4)
From
Date
Changelog v4
1. Add max_unmapped_ratio and use that as the upper limit
to check when to shrink the unmapped page cache (Christoph
Lameter)

Changelog v2
1. Use a config option to enable the code (Andrew Morton)
2. Explain the magic tunables in the code or at-least attempt
to explain them (General comment)
3. Hint uses of the boot parameter with unlikely (Andrew Morton)
4. Use better names (balanced is not a good naming convention)

Provide control using zone_reclaim() and a boot parameter. The
code reuses functionality from zone_reclaim() to isolate unmapped
pages and reclaim them as a priority, ahead of other mapped pages.
A new sysctl for max_unmapped_ratio is provided and set to 16,
indicating 16% of the total zone pages are unmapped, we start
shrinking unmapped page cache.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---
Documentation/kernel-parameters.txt | 8 +++
include/linux/mmzone.h | 5 ++
include/linux/swap.h | 23 ++++++++-
init/Kconfig | 12 +++++
kernel/sysctl.c | 11 ++++
mm/page_alloc.c | 25 ++++++++++
mm/vmscan.c | 87 +++++++++++++++++++++++++++++++++++
7 files changed, 166 insertions(+), 5 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index fee5f57..65a4ee6 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2500,6 +2500,14 @@ and is between 256 and 4096 characters. It is defined in the file
[X86]
Set unknown_nmi_panic=1 early on boot.

+ unmapped_page_control
+ [KNL] Available if CONFIG_UNMAPPED_PAGECACHE_CONTROL
+ is enabled. It controls the amount of unmapped memory
+ that is present in the system. This boot option plus
+ vm.min_unmapped_ratio (sysctl) provide granular control
+ over how much unmapped page cache can exist in the system
+ before kswapd starts reclaiming unmapped page cache pages.
+
usbcore.autosuspend=
[USB] The autosuspend time delay (in seconds) used
for newly-detected USB devices (default 2). This
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 2485acc..18f0f09 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -306,7 +306,10 @@ struct zone {
/*
* zone reclaim becomes active if more unmapped pages exist.
*/
+#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
unsigned long min_unmapped_pages;
+ unsigned long max_unmapped_pages;
+#endif
#ifdef CONFIG_NUMA
int node;
unsigned long min_slab_pages;
@@ -773,6 +776,8 @@ int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
int sysctl_min_unmapped_ratio_sysctl_handler(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
+int sysctl_max_unmapped_ratio_sysctl_handler(struct ctl_table *, int,
+ void __user *, size_t *, loff_t *);
int sysctl_min_slab_ratio_sysctl_handler(struct ctl_table *, int,
void __user *, size_t *, loff_t *);

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 7b75626..ae62a03 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -255,19 +255,34 @@ extern int vm_swappiness;
extern int remove_mapping(struct address_space *mapping, struct page *page);
extern long vm_total_pages;

+#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL) || defined(CONFIG_NUMA)
extern int sysctl_min_unmapped_ratio;
+extern int sysctl_max_unmapped_ratio;
+
extern int zone_reclaim(struct zone *, gfp_t, unsigned int);
-#ifdef CONFIG_NUMA
-extern int zone_reclaim_mode;
-extern int sysctl_min_slab_ratio;
#else
-#define zone_reclaim_mode 0
static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
{
return 0;
}
#endif

+#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL)
+extern bool should_reclaim_unmapped_pages(struct zone *zone);
+#else
+static inline bool should_reclaim_unmapped_pages(struct zone *zone)
+{
+ return false;
+}
+#endif
+
+#ifdef CONFIG_NUMA
+extern int zone_reclaim_mode;
+extern int sysctl_min_slab_ratio;
+#else
+#define zone_reclaim_mode 0
+#endif
+
extern int page_evictable(struct page *page, struct vm_area_struct *vma);
extern void scan_mapping_unevictable_pages(struct address_space *);

diff --git a/init/Kconfig b/init/Kconfig
index 4f6cdbf..2dfbc09 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -828,6 +828,18 @@ config SCHED_AUTOGROUP
config MM_OWNER
bool

+config UNMAPPED_PAGECACHE_CONTROL
+ bool "Provide control over unmapped page cache"
+ default n
+ help
+ This option adds support for controlling unmapped page cache
+ via a boot parameter (unmapped_page_control). The boot parameter
+ with sysctl (vm.min_unmapped_ratio) control the total number
+ of unmapped pages in the system. This feature is useful if
+ you want to limit the amount of unmapped page cache or want
+ to reduce page cache duplication in a virtualized environment.
+ If unsure say 'N'
+
config SYSFS_DEPRECATED
bool "enable deprecated sysfs features to support old userspace tools"
depends on SYSFS
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 12e8f26..63dbba6 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1224,6 +1224,7 @@ static struct ctl_table vm_table[] = {
.extra1 = &zero,
},
#endif
+#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
{
.procname = "min_unmapped_ratio",
.data = &sysctl_min_unmapped_ratio,
@@ -1233,6 +1234,16 @@ static struct ctl_table vm_table[] = {
.extra1 = &zero,
.extra2 = &one_hundred,
},
+ {
+ .procname = "max_unmapped_ratio",
+ .data = &sysctl_max_unmapped_ratio,
+ .maxlen = sizeof(sysctl_max_unmapped_ratio),
+ .mode = 0644,
+ .proc_handler = sysctl_max_unmapped_ratio_sysctl_handler,
+ .extra1 = &zero,
+ .extra2 = &one_hundred,
+ },
+#endif
#ifdef CONFIG_NUMA
{
.procname = "zone_reclaim_mode",
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7b56473..2ac8549 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1660,6 +1660,9 @@ zonelist_scan:
unsigned long mark;
int ret;

+ if (should_reclaim_unmapped_pages(zone))
+ wakeup_kswapd(zone, order, classzone_idx);
+
mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
if (zone_watermark_ok(zone, order, mark,
classzone_idx, alloc_flags))
@@ -4167,8 +4170,12 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,

zone->spanned_pages = size;
zone->present_pages = realsize;
+#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
zone->min_unmapped_pages = (realsize*sysctl_min_unmapped_ratio)
/ 100;
+ zone->max_unmapped_pages = (realsize*sysctl_max_unmapped_ratio)
+ / 100;
+#endif
#ifdef CONFIG_NUMA
zone->node = nid;
zone->min_slab_pages = (realsize * sysctl_min_slab_ratio) / 100;
@@ -5084,6 +5091,7 @@ int min_free_kbytes_sysctl_handler(ctl_table *table, int write,
return 0;
}

+#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
int sysctl_min_unmapped_ratio_sysctl_handler(ctl_table *table, int write,
void __user *buffer, size_t *length, loff_t *ppos)
{
@@ -5100,6 +5108,23 @@ int sysctl_min_unmapped_ratio_sysctl_handler(ctl_table *table, int write,
return 0;
}

+int sysctl_max_unmapped_ratio_sysctl_handler(ctl_table *table, int write,
+ void __user *buffer, size_t *length, loff_t *ppos)
+{
+ struct zone *zone;
+ int rc;
+
+ rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
+ if (rc)
+ return rc;
+
+ for_each_zone(zone)
+ zone->max_unmapped_pages = (zone->present_pages *
+ sysctl_max_unmapped_ratio) / 100;
+ return 0;
+}
+#endif
+
#ifdef CONFIG_NUMA
int sysctl_min_slab_ratio_sysctl_handler(ctl_table *table, int write,
void __user *buffer, size_t *length, loff_t *ppos)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 02cc82e..6377411 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -159,6 +159,29 @@ static DECLARE_RWSEM(shrinker_rwsem);
#define scanning_global_lru(sc) (1)
#endif

+#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL)
+static unsigned long reclaim_unmapped_pages(int priority, struct zone *zone,
+ struct scan_control *sc);
+static int unmapped_page_control __read_mostly;
+
+static int __init unmapped_page_control_parm(char *str)
+{
+ unmapped_page_control = 1;
+ /*
+ * XXX: Should we tweak swappiness here?
+ */
+ return 1;
+}
+__setup("unmapped_page_control", unmapped_page_control_parm);
+
+#else /* !CONFIG_UNMAPPED_PAGECACHE_CONTROL */
+static inline unsigned long reclaim_unmapped_pages(int priority,
+ struct zone *zone, struct scan_control *sc)
+{
+ return 0;
+}
+#endif
+
static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
struct scan_control *sc)
{
@@ -2359,6 +2382,12 @@ loop_again:
shrink_active_list(SWAP_CLUSTER_MAX, zone,
&sc, priority, 0);

+ /*
+ * We do unmapped page reclaim once here and once
+ * below, so that we don't lose out
+ */
+ reclaim_unmapped_pages(priority, zone, &sc);
+
if (!zone_watermark_ok_safe(zone, order,
high_wmark_pages(zone), 0, 0)) {
end_zone = i;
@@ -2396,6 +2425,11 @@ loop_again:
continue;

sc.nr_scanned = 0;
+ /*
+ * Reclaim unmapped pages upfront, this should be
+ * really cheap
+ */
+ reclaim_unmapped_pages(priority, zone, &sc);

/*
* Call soft limit reclaim before calling shrink_zone.
@@ -2715,7 +2749,8 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
}
if (!waitqueue_active(&pgdat->kswapd_wait))
return;
- if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
+ if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0) &&
+ !should_reclaim_unmapped_pages(zone))
return;

trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
@@ -2868,6 +2903,7 @@ static int __init kswapd_init(void)

module_init(kswapd_init)

+#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL) || defined(CONFIG_NUMA)
/*
* Zone reclaim mode
*
@@ -2893,6 +2929,7 @@ int zone_reclaim_mode __read_mostly;
* occur.
*/
int sysctl_min_unmapped_ratio = 1;
+int sysctl_max_unmapped_ratio = 16;

/*
* If the number of slab pages in a zone grows beyond this percentage then
@@ -3088,6 +3125,54 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)

return ret;
}
+#endif
+
+#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL)
+/*
+ * Routine to reclaim unmapped pages, inspired from the code under
+ * CONFIG_NUMA that does unmapped page and slab page control by keeping
+ * min_unmapped_pages in the zone. We currently reclaim just unmapped
+ * pages, slab control will come in soon, at which point this routine
+ * should be called reclaim cached pages
+ */
+unsigned long reclaim_unmapped_pages(int priority, struct zone *zone,
+ struct scan_control *sc)
+{
+ if (unlikely(unmapped_page_control) &&
+ (zone_unmapped_file_pages(zone) > zone->min_unmapped_pages)) {
+ struct scan_control nsc;
+ unsigned long nr_pages;
+
+ nsc = *sc;
+
+ nsc.swappiness = 0;
+ nsc.may_writepage = 0;
+ nsc.may_unmap = 0;
+ nsc.nr_reclaimed = 0;
+
+ nr_pages = zone_unmapped_file_pages(zone) -
+ zone->min_unmapped_pages;
+ /*
+ * We don't want to be too aggressive with our
+ * reclaim, it is our best effort to control
+ * unmapped pages
+ */
+ nr_pages >>= 3;
+
+ zone_reclaim_pages(zone, &nsc, nr_pages);
+ return nsc.nr_reclaimed;
+ }
+ return 0;
+}
+
+bool should_reclaim_unmapped_pages(struct zone *zone)
+{
+ if (unlikely(unmapped_page_control) &&
+ (zone_unmapped_file_pages(zone) > zone->max_unmapped_pages))
+ return true;
+ return false;
+}
+#endif

/*
* page_evictable - test whether a page is evictable


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