[patch 12/19] scan noreclaim list for reclaimable pages

From: Rik van Riel
Date: Tue Jan 08 2008 - 16:19:36 EST

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V2 -> V3:
+ rebase to 23-mm1 atop RvR's split LRU series

New in V2

This patch adds a function to scan individual or all zones' noreclaim
lists and move any pages that have become reclaimable onto the respective
zone's inactive list, where shrink_inactive_list() will deal with them.

This replaces the function to splice the entire noreclaim list onto the
active list for rescan by shrink_active_list(). That method had problems
with vmstat accounting and complicated '[__]isolate_lru_pages()'. Now,
__isolate_lru_page() will never isolate a non-reclaimable page. The
only time it should see one is when scanning nearby pages for lumpy
reclaim.

TODO: This approach may still need some refinement.
E.g., put back to active list?

DEBUGGING ONLY: NOT FOR UPSTREAM MERGE

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@xxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>

Index: linux-2.6.24-rc6-mm1/include/linux/swap.h
===================================================================
--- linux-2.6.24-rc6-mm1.orig/include/linux/swap.h 2008-01-08 12:17:10.000000000 -0500
+++ linux-2.6.24-rc6-mm1/include/linux/swap.h 2008-01-08 12:17:17.000000000 -0500
@@ -7,6 +7,7 @@
#include <linux/list.h>
#include <linux/sched.h>
#include <linux/memcontrol.h>
+#include <linux/node.h>

#include <asm/atomic.h>
#include <asm/page.h>
@@ -215,12 +216,26 @@ static inline int zone_reclaim(struct zo

#ifdef CONFIG_NORECLAIM
extern int page_reclaimable(struct page *page, struct vm_area_struct *vma);
+extern void scan_zone_noreclaim_pages(struct zone *);
+extern void scan_all_zones_noreclaim_pages(void);
+extern unsigned long scan_noreclaim_pages;
+extern int scan_noreclaim_handler(struct ctl_table *, int, struct file *,
+ void __user *, size_t *, loff_t *);
+extern int scan_noreclaim_register_node(struct node *node);
+extern void scan_noreclaim_unregister_node(struct node *node);
#else
static inline int page_reclaimable(struct page *page,
struct vm_area_struct *vma)
{
return 1;
}
+static inline void scan_zone_noreclaim_pages(struct zone *z) { }
+static inline void scan_all_zones_noreclaim_pages(void) { }
+static inline int scan_noreclaim_register_node(struct node *node)
+{
+ return 0;
+}
+static inline void scan_noreclaim_unregister_node(struct node *node) { }
#endif

extern int kswapd_run(int nid);
Index: linux-2.6.24-rc6-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/vmscan.c 2008-01-08 12:17:10.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/vmscan.c 2008-01-08 12:17:17.000000000 -0500
@@ -39,6 +39,7 @@
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/memcontrol.h>
+#include <linux/sysctl.h>

#include <asm/tlbflush.h>
#include <asm/div64.h>
@@ -2270,4 +2271,144 @@ int page_reclaimable(struct page *page,

return 1;
}
+
+/**
+ * scan_zone_noreclaim_pages(@zone)
+ * @zone - zone to scan
+ *
+ * Scan @zone's noreclaim LRU lists to check for pages that have become
+ * reclaimable. Move those that have to @zone's inactive list where they
+ * become candidates for reclaim, unless shrink_inactive_zone() decides
+ * to reactivate them. Pages that are still non-reclaimable are rotated
+ * back onto @zone's noreclaim list.
+ */
+#define SCAN_NORECLAIM_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
+void scan_zone_noreclaim_pages(struct zone *zone)
+{
+ struct list_head *l_noreclaim = &zone->list[LRU_NORECLAIM];
+ struct list_head *l_inactive_anon = &zone->list[LRU_INACTIVE_ANON];
+ struct list_head *l_inactive_file = &zone->list[LRU_INACTIVE_FILE];
+ unsigned long scan;
+ unsigned long nr_to_scan = zone_page_state(zone, NR_NORECLAIM);
+
+ while (nr_to_scan > 0) {
+ unsigned long batch_size = min(nr_to_scan,
+ SCAN_NORECLAIM_BATCH_SIZE);
+
+ spin_lock_irq(&zone->lru_lock);
+ for (scan = 0; scan < batch_size; scan++) {
+ struct page* page = lru_to_page(l_noreclaim);
+
+ if (unlikely(!PageLRU(page) || !PageNoreclaim(page)))
+ continue;
+
+ prefetchw_prev_lru_page(page, l_noreclaim, flags);
+
+ ClearPageNoreclaim(page); /* for page_reclaimable() */
+ if(page_reclaimable(page, NULL)) {
+ __dec_zone_state(zone, NR_NORECLAIM);
+ if (page_file_cache(page)) {
+ list_move(&page->lru, l_inactive_file);
+ __inc_zone_state(zone, NR_INACTIVE_FILE);
+ } else {
+ list_move(&page->lru, l_inactive_anon);
+ __inc_zone_state(zone, NR_INACTIVE_ANON);
+ }
+ } else {
+ SetPageNoreclaim(page);
+ list_move(&page->lru, l_noreclaim);
+ }
+
+ }
+ spin_unlock_irq(&zone->lru_lock);
+
+ nr_to_scan -= batch_size;
+ }
+}
+
+
+/**
+ * scan_all_zones_noreclaim_pages()
+ *
+ * A really big hammer: scan all zones' noreclaim LRU lists to check for
+ * pages that have become reclaimable. Move those back to the zones'
+ * inactive list where they become candidates for reclaim.
+ * This occurs when, e.g., we have unswappable pages on the noreclaim lists,
+ * and we add swap to the system. As such, it runs in the context of a task
+ * that has possibly/probably made some previously non-reclaimable pages
+ * reclaimable.
+//TODO: or as a last resort under extreme memory pressure--before OOM?
+ */
+void scan_all_zones_noreclaim_pages(void)
+{
+ struct zone *zone;
+
+ for_each_zone(zone) {
+ scan_zone_noreclaim_pages(zone);
+ }
+}
+
+/*
+ * scan_noreclaim_pages [vm] sysctl handler. On demand re-scan of
+ * all nodes' noreclaim lists for reclaimable pages
+ */
+unsigned long scan_noreclaim_pages;
+
+int scan_noreclaim_handler( struct ctl_table *table, int write,
+ struct file *file, void __user *buffer,
+ size_t *length, loff_t *ppos)
+{
+ proc_doulongvec_minmax(table, write, file, buffer, length, ppos);
+
+ if (write && *(unsigned long *)table->data)
+ scan_all_zones_noreclaim_pages();
+
+ scan_noreclaim_pages = 0;
+ return 0;
+}
+
+/*
+ * per node 'scan_noreclaim_pages' attribute. On demand re-scan of
+ * a specified node's per zone noreclaim lists for reclaimable pages.
+ */
+
+static ssize_t read_scan_noreclaim_node(struct sys_device *dev, char *buf)
+{
+ return sprintf(buf, "0\n"); /* always zero; should fit... */
+}
+
+static ssize_t write_scan_noreclaim_node(struct sys_device *dev,
+ const char *buf, size_t count)
+{
+ struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
+ struct zone *zone;
+ unsigned long req = simple_strtoul(buf, NULL, 10);
+
+ if (!req)
+ return 1; /* zero is no-op */
+
+ for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
+ if (!populated_zone(zone))
+ continue;
+ scan_zone_noreclaim_pages(zone);
+ }
+ return 1;
+}
+
+
+static SYSDEV_ATTR(scan_noreclaim_pages, S_IRUGO | S_IWUSR,
+ read_scan_noreclaim_node,
+ write_scan_noreclaim_node);
+
+int scan_noreclaim_register_node(struct node *node)
+{
+ return sysdev_create_file(&node->sysdev, &attr_scan_noreclaim_pages);
+}
+
+void scan_noreclaim_unregister_node(struct node *node)
+{
+ sysdev_remove_file(&node->sysdev, &attr_scan_noreclaim_pages);
+}
+
+
#endif
Index: linux-2.6.24-rc6-mm1/kernel/sysctl.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/kernel/sysctl.c 2008-01-08 12:08:02.000000000 -0500
+++ linux-2.6.24-rc6-mm1/kernel/sysctl.c 2008-01-08 12:17:17.000000000 -0500
@@ -1151,6 +1151,16 @@ static struct ctl_table vm_table[] = {
.extra2 = &one,
},
#endif
+#ifdef CONFIG_NORECLAIM
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "scan_noreclaim_pages",
+ .data = &scan_noreclaim_pages,
+ .maxlen = sizeof(scan_noreclaim_pages),
+ .mode = 0644,
+ .proc_handler = &scan_noreclaim_handler,
+ },
+#endif
/*
* NOTE: do not add new entries to this table unless you have read
* Documentation/sysctl/ctl_unnumbered.txt
Index: linux-2.6.24-rc6-mm1/drivers/base/node.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/drivers/base/node.c 2008-01-08 12:17:14.000000000 -0500
+++ linux-2.6.24-rc6-mm1/drivers/base/node.c 2008-01-08 12:17:17.000000000 -0500
@@ -13,6 +13,7 @@
#include <linux/nodemask.h>
#include <linux/cpu.h>
#include <linux/device.h>
+#include <linux/swap.h>

static struct sysdev_class node_class = {
.name = "node",
@@ -162,6 +163,8 @@ int register_node(struct node *node, int
sysdev_create_file(&node->sysdev, &attr_meminfo);
sysdev_create_file(&node->sysdev, &attr_numastat);
sysdev_create_file(&node->sysdev, &attr_distance);
+
+ scan_noreclaim_register_node(node);
}
return error;
}
@@ -180,6 +183,8 @@ void unregister_node(struct node *node)
sysdev_remove_file(&node->sysdev, &attr_numastat);
sysdev_remove_file(&node->sysdev, &attr_distance);

+ scan_noreclaim_unregister_node(node);
+
sysdev_unregister(&node->sysdev);
}

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Next message: Rik van Riel: "[patch 15/19] non-reclaimable mlocked pages"
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