[PATCH] vm thrashing control tuning

This patch adds "swap_token_timeout" parameter in /proc/sys/vm.  The
parameter means expired time of token.  Unit of the value is HZ, and the
default value is the same as current SWAP_TOKEN_TIMEOUT (i.e.  HZ * 300).
Signed-off-by: Hideo Aoki <aoki@sdl.hitachi.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Documentation/filesystems/proc.txt

@@ -1295,6 +1295,14 @@ block_dump
 block_dump enables block I/O debugging when set to a nonzero value. More
 information on block I/O debugging is in Documentation/laptop-mode.txt.
 
+swap_token_timeout
+------------------
+
+This file contains valid hold time of swap out protection token. The Linux
+VM has token based thrashing control mechanism and uses the token to prevent
+unnecessary page faults in thrashing situation. The unit of the value is
+second. The value would be useful to tune thrashing behavior.
+
 2.5 /proc/sys/dev - Device specific parameters
 ----------------------------------------------
 

Documentation/sysctl/vm.txt

@@ -31,7 +31,7 @@ Currently, these files are in /proc/sys/vm:
 
 dirty_ratio, dirty_background_ratio, dirty_expire_centisecs,
 dirty_writeback_centisecs, vfs_cache_pressure, laptop_mode,
-block_dump:
+block_dump, swap_token_timeout:
 
 See Documentation/filesystems/proc.txt
 

include/linux/swap.h

@@ -230,6 +230,7 @@ extern spinlock_t swaplock;
 
 /* linux/mm/thrash.c */
 extern struct mm_struct * swap_token_mm;
+extern unsigned long swap_token_default_timeout;
 extern void grab_swap_token(void);
 extern void __put_swap_token(struct mm_struct *);
 

include/linux/sysctl.h

@@ -167,6 +167,7 @@ enum
 	VM_HUGETLB_GROUP=25,	/* permitted hugetlb group */
 	VM_VFS_CACHE_PRESSURE=26, /* dcache/icache reclaim pressure */
 	VM_LEGACY_VA_LAYOUT=27, /* legacy/compatibility virtual address space layout */
+	VM_SWAP_TOKEN_TIMEOUT=28, /* default time for token time out */
 };
 
 

kernel/sysctl.c

@@ -783,6 +783,7 @@ static ctl_table vm_table[] = {
 		.strategy	= &sysctl_intvec,
 		.extra1		= &zero,
 	},
+#ifdef CONFIG_SWAP
 	{
 		.ctl_name	= VM_VFS_CACHE_PRESSURE,
 		.procname	= "vfs_cache_pressure",
@@ -805,6 +806,15 @@ static ctl_table vm_table[] = {
 		.extra1		= &zero,
 	},
 #endif
+	{
+		.ctl_name	= VM_SWAP_TOKEN_TIMEOUT,
+		.procname	= "swap_token_timeout",
+		.data		= &swap_token_default_timeout,
+		.maxlen		= sizeof(swap_token_default_timeout),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec_jiffies,
+		.strategy	= &sysctl_jiffies,
+	},
 	{ .ctl_name = 0 }
 };
 
@@ -915,6 +925,7 @@ static ctl_table fs_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
+#endif
 	{ .ctl_name = 0 }
 };
 

mm/thrash.c

@@ -20,6 +20,7 @@ struct mm_struct * swap_token_mm = &init_mm;
 
 #define SWAP_TOKEN_CHECK_INTERVAL (HZ * 2)
 #define SWAP_TOKEN_TIMEOUT (HZ * 300)
+unsigned long swap_token_default_timeout = SWAP_TOKEN_TIMEOUT;
 
 /*
  * Take the token away if the process had no page faults
@@ -75,10 +76,10 @@ void grab_swap_token(void)
 		if ((reason = should_release_swap_token(mm))) {
 			unsigned long eligible = jiffies;
 			if (reason == SWAP_TOKEN_TIMED_OUT) {
-				eligible += SWAP_TOKEN_TIMEOUT;
+				eligible += swap_token_default_timeout;
 			}
 			mm->swap_token_time = eligible;
-			swap_token_timeout = jiffies + SWAP_TOKEN_TIMEOUT;
+			swap_token_timeout = jiffies + swap_token_default_timeout;
 			swap_token_mm = current->mm;
 		}
 		spin_unlock(&swap_token_lock);