[PATCH 2/2] VM throttling: Add vm.dirty_start_writeback_ratio to sysctl

[Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>]

This patch adds a sysctl variable `vm.dirty_start_writeback_ratio' to
enable users to adjust the writeback starting level of the dirty pages.

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
---
 Documentation/filesystems/proc.txt |   11 +++++++++--
 Documentation/sysctl/vm.txt        |    3 ++-
 kernel/sysctl.c                    |   11 +++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

Index: linux-2.6.21-rc5-mm3-writeback/Documentation/filesystems/proc.txt
===================================================================
--- linux-2.6.21-rc5-mm3-writeback.orig/Documentation/filesystems/proc.txt
+++ linux-2.6.21-rc5-mm3-writeback/Documentation/filesystems/proc.txt
@@ -1170,13 +1170,20 @@ dirty_background_ratio
 Contains, as a percentage of total system memory, the number of pages at which
 the pdflush background writeback daemon will start writing out dirty data.

-dirty_ratio
------------------
+dirty_writeback_start_ratio
+---------------------------

 Contains, as a percentage of total system memory, the number of pages at which
 a process which is generating disk writes will itself start writing out dirty
 data.

+dirty_ratio
+-----------------
+
+Contains, as a percentage of total system memory, the number of pages at which
+a process which is generating disk writes will be blocked untill the level
+subsides.
+
 dirty_writeback_centisecs
 -------------------------

Index: linux-2.6.21-rc5-mm3-writeback/Documentation/sysctl/vm.txt
===================================================================
--- linux-2.6.21-rc5-mm3-writeback.orig/Documentation/sysctl/vm.txt
+++ linux-2.6.21-rc5-mm3-writeback/Documentation/sysctl/vm.txt
@@ -19,6 +19,7 @@ Currently, these files are in /proc/sys/
 - overcommit_memory
 - page-cluster
 - dirty_ratio
+- dirty_start_writeback_ratio
 - dirty_background_ratio
 - dirty_expire_centisecs
 - dirty_writeback_centisecs
@@ -40,7 +41,7 @@ Currently, these files are in /proc/sys/
 dirty_ratio, dirty_background_ratio, dirty_expire_centisecs,
 dirty_writeback_centisecs, vfs_cache_pressure, laptop_mode,
 block_dump, swap_token_timeout, drop-caches,
-hugepages_treat_as_movable:
+hugepages_treat_as_movable, dirty_start_writeback_ratio:

 See Documentation/filesystems/proc.txt

Index: linux-2.6.21-rc5-mm3-writeback/kernel/sysctl.c
===================================================================
--- linux-2.6.21-rc5-mm3-writeback.orig/kernel/sysctl.c
+++ linux-2.6.21-rc5-mm3-writeback/kernel/sysctl.c
@@ -708,6 +708,17 @@ static ctl_table vm_table[] = {
 		.extra2		= &one_hundred,
 	},
 	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "dirty_start_writeback_ratio",
+		.data		= &dirty_start_writeback_ratio,
+		.maxlen		= sizeof(dirty_start_writeback_ratio),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec_minmax,
+		.strategy	= &sysctl_intvec,
+		.extra1		= &zero,
+		.extra2		= &one_hundred,
+	},
+	{
 		.ctl_name	= VM_DIRTY_WB_CS,
 		.procname	= "dirty_writeback_centisecs",
 		.data		= &dirty_writeback_interval,