Re: [PATCH 2.6.17-rc1-mm1 8/9] AutoPage Migration - V0.2 - add max mapcount migration threshold

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

AutoPage Migration - V0.2 - 8/9 add max mapcount migration threshold

This patch adds an additional migration control that allows one
to vary the page mapcount threshold above which pages will not
be migrated by MPOL_MF_MOVE.  The default value is 1, which yields
the same behavior as before this patch.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

Index: linux-2.6.16-mm1/include/linux/auto-migrate.h
===================================================================
--- linux-2.6.16-mm1.orig/include/linux/auto-migrate.h	2006-03-23 16:50:24.000000000 -0500
+++ linux-2.6.16-mm1/include/linux/auto-migrate.h	2006-03-23 16:50:30.000000000 -0500
@@ -20,6 +20,8 @@ extern unsigned long auto_migrate_interv
 #define AUTO_MIGRATE_INTERVAL_MIN (5*HZ)
 #define AUTO_MIGRATE_INTERVAL_MAX (300*HZ)
 
+extern unsigned int migrate_max_mapcount;
+
 #ifdef _LINUX_SCHED_H	/* only used where this is defined */
 static inline void check_internode_migration(task_t *task, int dest_cpu)
 {
@@ -98,6 +100,7 @@ out:
 #define too_soon_for_internode_migration(t,c) 0
 
 #define check_migrate_pending()		/* NOTHING */
+#define migrate_max_mapcount (1)
 
 #endif	/* CONFIG_MIGRATION */
 
Index: linux-2.6.16-mm1/mm/migrate.c
===================================================================
--- linux-2.6.16-mm1.orig/mm/migrate.c	2006-03-23 16:50:24.000000000 -0500
+++ linux-2.6.16-mm1/mm/migrate.c	2006-03-23 16:50:30.000000000 -0500
@@ -107,12 +107,35 @@ static ssize_t auto_migrate_interval_sto
 }
 MIGRATION_ATTR_RW(auto_migrate_interval);
 
+/*
+ * migrate_max_mapcount:  specify how many mappers allowed
+ * before we won't migrate a page via MPOL_MF_MOVE.
+ */
+unsigned int migrate_max_mapcount = 1;	/* default == minimum */
+
+static ssize_t migrate_max_mapcount_show(struct subsystem *subsys, char *page)
+{
+	return sprintf(page, "migrate_max_mapcount %d\n", migrate_max_mapcount);
+}
+static ssize_t migrate_max_mapcount_store(struct subsystem *subsys,
+				      const char *page, size_t count)
+{
+        unsigned int n = simple_strtoul(page, NULL, 10);
+	if (n < 1)
+		migrate_max_mapcount = 1;
+	else
+		migrate_max_mapcount = n;
+        return count;
+}
+MIGRATION_ATTR_RW(migrate_max_mapcount);
+
 decl_subsys(migration, NULL, NULL);
 EXPORT_SYMBOL(migration_subsys);
 
 static struct attribute *migration_attrs[] = {
 	&auto_migrate_enable_attr.attr,
 	&auto_migrate_interval_attr.attr,
+	&migrate_max_mapcount_attr.attr,
 	NULL
 };
 
Index: linux-2.6.16-mm1/mm/mempolicy.c
===================================================================
--- linux-2.6.16-mm1.orig/mm/mempolicy.c	2006-03-23 16:49:34.000000000 -0500
+++ linux-2.6.16-mm1/mm/mempolicy.c	2006-03-23 16:50:30.000000000 -0500
@@ -87,6 +87,7 @@
 #include <linux/seq_file.h>
 #include <linux/proc_fs.h>
 #include <linux/migrate.h>
+#include <linux/auto-migrate.h>
 
 #include <asm/tlbflush.h>
 #include <asm/uaccess.h>
@@ -452,7 +453,6 @@ static int contextualize_policy(int mode
 	return mpol_check_policy(mode, nodes);
 }
 
-
 /*
  * Update task->flags PF_MEMPOLICY bit: set iff non-default
  * mempolicy.  Allows more rapid checking of this (combined perhaps
@@ -611,9 +611,10 @@ static void migrate_page_add(struct page
 				unsigned long flags)
 {
 	/*
-	 * Avoid migrating a page that is shared with others.
+	 * Avoid migrating a page that is shared with [too many] others.
 	 */
-	if ((flags & MPOL_MF_MOVE_ALL) || page_mapcount(page) == 1)
+	if ((flags & MPOL_MF_MOVE_ALL) ||
+		page_mapcount(page) <= migrate_max_mapcount)
 		isolate_lru_page(page, pagelist);
 }
 


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