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Subject[PATCH 2/2] writeback: Adding pages_dirtied and pages_entered_writeback
Date
To help developers and applications gain visibility into writeback
behaviour adding four read only sysctl files into /proc/sys/vm.
These files allow user apps to understand writeback behaviour over time
and learn how it is impacting their performance.

# cat /proc/sys/vm/pages_dirtied
3747
# cat /proc/sys/vm/pages_entered_writeback
3618

Documentation/vm.txt has been updated.

In order to track the "cleaned" and "dirtied" counts we added two
vm_stat_items. Per memory node stats have been added also. So we can
see per node granularity:

# cat /sys/devices/system/node/node20/writebackstat
Node 20 pages_writeback: 0 times
Node 20 pages_dirtied: 0 times

Signed-off-by: Michael Rubin <mrubin@google.com>
---
Documentation/sysctl/vm.txt | 20 ++++++++++++++++----
drivers/base/node.c | 14 ++++++++++++++
include/linux/mmzone.h | 2 ++
include/linux/writeback.h | 9 +++++++++
kernel/sysctl.c | 14 ++++++++++++++
mm/page-writeback.c | 36 ++++++++++++++++++++++++++++++------
mm/vmstat.c | 2 ++
7 files changed, 87 insertions(+), 10 deletions(-)
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 5fdbb61..de9ec6a 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -50,6 +50,8 @@ Currently, these files are in /proc/sys/vm:
- overcommit_memory
- overcommit_ratio
- page-cluster
+- pages_dirtied
+- pages_entered_writeback
- panic_on_oom
- percpu_pagelist_fraction
- stat_interval
@@ -425,10 +427,7 @@ See Documentation/vm/hugetlbpage.txt
nr_pdflush_threads

The current number of pdflush threads. This value is read-only.
-The value changes according to the number of dirty pages in the system.
-
-When necessary, additional pdflush threads are created, one per second, up to
-nr_pdflush_threads_max.
+This value is obsolete.

==============================================================

@@ -582,6 +581,19 @@ swap-intensive.

=============================================================

+pages_dirtied
+
+Number of pages that have ever been dirtied since boot.
+This value is read-only.
+
+=============================================================
+
+pages_entered_writeback
+
+Number of pages that have been moved from dirty to writeback since boot.
+This is only a count of file pages. This value is read-only.
+
+=============================================================
panic_on_oom

This enables or disables panic on out-of-memory feature.
diff --git a/drivers/base/node.c b/drivers/base/node.c
index 2bdd8a9..b321d32 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -160,6 +160,18 @@ static ssize_t node_read_numastat(struct sys_device * dev,
}
static SYSDEV_ATTR(numastat, S_IRUGO, node_read_numastat, NULL);

+static ssize_t node_read_writebackstat(struct sys_device *dev,
+ struct sysdev_attribute *attr, char *buf)
+{
+ int nid = dev->id;
+ return sprintf(buf,
+ "Node %d pages_writeback: %lu times\n"
+ "Node %d pages_dirtied: %lu times\n",
+ nid, node_page_state(nid, NR_PAGES_ENTERED_WRITEBACK),
+ nid, node_page_state(nid, NR_FILE_PAGES_DIRTIED));
+}
+static SYSDEV_ATTR(writebackstat, S_IRUGO, node_read_writebackstat, NULL);
+
static ssize_t node_read_distance(struct sys_device * dev,
struct sysdev_attribute *attr, char * buf)
{
@@ -243,6 +255,7 @@ int register_node(struct node *node, int num, struct node *parent)
sysdev_create_file(&node->sysdev, &attr_meminfo);
sysdev_create_file(&node->sysdev, &attr_numastat);
sysdev_create_file(&node->sysdev, &attr_distance);
+ sysdev_create_file(&node->sysdev, &attr_writebackstat);

scan_unevictable_register_node(node);

@@ -267,6 +280,7 @@ void unregister_node(struct node *node)
sysdev_remove_file(&node->sysdev, &attr_meminfo);
sysdev_remove_file(&node->sysdev, &attr_numastat);
sysdev_remove_file(&node->sysdev, &attr_distance);
+ sysdev_remove_file(&node->sysdev, &attr_writebackstat);

scan_unevictable_unregister_node(node);
hugetlb_unregister_node(node); /* no-op, if memoryless node */
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b4d109e..c0cd2bd 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -112,6 +112,8 @@ enum zone_stat_item {
NUMA_LOCAL, /* allocation from local node */
NUMA_OTHER, /* allocation from other node */
#endif
+ NR_PAGES_ENTERED_WRITEBACK, /* number of times pages enter writeback */
+ NR_FILE_PAGES_DIRTIED, /* number of times pages get dirtied */
NR_VM_ZONE_STAT_ITEMS };

/*
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index c24eca7..2d47afb 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -99,6 +99,8 @@ extern int dirty_background_ratio;
extern unsigned long dirty_background_bytes;
extern int vm_dirty_ratio;
extern unsigned long vm_dirty_bytes;
+extern unsigned long vm_pages_dirtied;
+extern unsigned long vm_pages_entered_writeback;
extern unsigned int dirty_writeback_interval;
extern unsigned int dirty_expire_interval;
extern int vm_highmem_is_dirtyable;
@@ -120,6 +122,13 @@ extern int dirty_bytes_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos);

+extern int pages_dirtied_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos);
+extern int pages_entered_writeback_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos);
+
struct ctl_table;
int dirty_writeback_centisecs_handler(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index d24f761..33c3589 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1053,6 +1053,20 @@ static struct ctl_table vm_table[] = {
.proc_handler = proc_dointvec,
},
{
+ .procname = "pages_dirtied",
+ .data = &vm_pages_dirtied,
+ .maxlen = sizeof(vm_pages_dirtied),
+ .mode = 0444 /* read-only */,
+ .proc_handler = pages_dirtied_handler,
+ },
+ {
+ .procname = "pages_entered_writeback",
+ .data = &vm_pages_entered_writeback,
+ .maxlen = sizeof(vm_pages_entered_writeback),
+ .mode = 0444 /* read-only */,
+ .proc_handler = pages_entered_writeback_handler,
+ },
+ {
.procname = "nr_pdflush_threads",
.data = &nr_pdflush_threads,
.maxlen = sizeof nr_pdflush_threads,
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b8e7b3b..4ed5dec 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -95,6 +95,14 @@ unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
*/
unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */

+
+/*
+ * Number of pages dirtied and entered writeback state
+ */
+
+unsigned long vm_pages_dirtied;
+unsigned long vm_pages_entered_writeback;
+
/*
* Flag that makes the machine dump writes/reads and block dirtyings.
*/
@@ -196,7 +204,6 @@ int dirty_ratio_handler(struct ctl_table *table, int write,
return ret;
}

-
int dirty_bytes_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos)
@@ -212,6 +219,23 @@ int dirty_bytes_handler(struct ctl_table *table, int write,
return ret;
}

+int pages_dirtied_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ vm_pages_dirtied = global_page_state(NR_FILE_PAGES_DIRTIED);
+ return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
+}
+
+int pages_entered_writeback_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ vm_pages_entered_writeback =
+ global_page_state(NR_PAGES_ENTERED_WRITEBACK);
+ return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
+}
+
/*
* Increment the BDI's writeout completion count and the global writeout
* completion count. Called from test_clear_page_writeback().
@@ -1091,6 +1115,7 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
{
if (mapping_cap_account_dirty(mapping)) {
__inc_zone_page_state(page, NR_FILE_DIRTY);
+ __inc_zone_page_state(page, NR_FILE_PAGES_DIRTIED);
__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
task_dirty_inc(current);
task_io_account_write(PAGE_CACHE_SIZE);
@@ -1103,15 +1128,15 @@ EXPORT_SYMBOL(account_page_dirtied);
* NOTE: Unlike account_page_dirtied this does not rely on being atomic
* wrt interrupts.
*/
-
void account_page_writeback(struct page *page, struct address_space *mapping)
{
- if (mapping_cap_account_dirty(mapping))
+ if (mapping_cap_account_dirty(mapping)) {
inc_zone_page_state(page, NR_WRITEBACK);
+ inc_zone_page_state(page, NR_PAGES_ENTERED_WRITEBACK);
+ }
}
EXPORT_SYMBOL(account_page_writeback);

-
/*
* For address_spaces which do not use buffers. Just tag the page as dirty in
* its radix tree.
@@ -1347,9 +1372,8 @@ int test_set_page_writeback(struct page *page)
ret = TestSetPageWriteback(page);
}
if (!ret)
- inc_zone_page_state(page, NR_WRITEBACK);
+ account_page_writeback(page, mapping);
return ret;
-
}
EXPORT_SYMBOL(test_set_page_writeback);

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 7759941..e177a40 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -740,6 +740,8 @@ static const char * const vmstat_text[] = {
"numa_local",
"numa_other",
#endif
+ "nr_pages_entered_writeback",
+ "nr_file_pages_dirtied",

#ifdef CONFIG_VM_EVENT_COUNTERS
"pgpgin",
--
1.7.1


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