[PATCH 0/5] writeback: kernel visibility

[PATCH 0/5] writeback: kernel visibility

[Michael Rubin]

Patch #1 sets up some helper functions for account_page_dirty and fixes
a bug in ceph

Patch #2 sets up some helper functions for account_page_writeback

Patch #3 adds writeback visibility in /proc/vmstat

To help developers and applications gain visibility into writeback
behaviour this patch adds two counters to /proc/vmstat.

  # grep nr_dirtied /proc/vmstat
  nr_dirtied 3747
  # grep nr_written /proc/vmstat
  nr_written 3618

These entries allow user apps to understand writeback behaviour over
time and learn how it is impacting their performance. Currently there
is no way to inspect dirty and writeback speed over time. It's not
possible for nr_dirty/nr_writeback.

These entries are necessary to give visibility into writeback
behaviour. We have /proc/diskstats which lets us understand the io in
the block layer. We have blktrace for more in depth understanding. We have
e2fsprogs and debugsfs to give insight into the file systems behaviour,
but we don't offer our users the ability understand what writeback is
doing. There is no way to know how active it is over the whole system,
if it's falling behind or to quantify it's efforts. With these values
exported users can easily see how much data applications are sending
through writeback and also at what rates writeback is processing this
data. Comparing the rates of change between the two allow developers
to see when writeback is not able to keep up with incoming traffic and
the rate of dirty memory being sent to the IO back end. This allows
folks to understand their io workloads and track kernel issues. Non
kernel engineers at Google often use these counters to solve puzzling
performance problems.

Patch #4 adds a pernode vmstat file with nr_dirtied and nr_written

Patch #5 add writeback thresholds to /proc/vmstat

Currently these values are in debugfs. But they should be promoted to
/proc since they are useful for developers who are writing databases
and file servers and are not debugging the kernel.

The output is as below:

 # grep threshold /proc/vmstat
 nr_pages_dirty_threshold 409111
 nr_pages_dirty_background_threshold 818223

Michael Rubin (5):
  mm: exporting account_page_dirty
  mm: account_page_writeback added
  writeback: nr_dirtied and nr_written in /proc/vmstat
  writeback: Adding /sys/devices/system/node/<node>/vmstat
  writeback: Reporting dirty thresholds in /proc/vmstat

 drivers/base/node.c    |   14 ++++++++++++++
 fs/ceph/addr.c         |    8 +-------
 fs/nilfs2/segment.c    |    2 +-
 include/linux/mm.h     |    1 +
 include/linux/mmzone.h |    4 ++++
 mm/page-writeback.c    |   16 +++++++++++++++-
 mm/vmstat.c            |    7 +++++++
 7 files changed, 43 insertions(+), 9 deletions(-)

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[PATCH 1/5] mm: exporting account_page_dirty

[Michael Rubin]

This allows code outside of the mm core to safely manipulate page state
and not worry about the other accounting. Not using these routines means
that some code will lose track of the accounting and we get bugs. This
has happened once already.

Modified cephs to use the interface.

Signed-off-by: Michael Rubin <mrubin@google.com>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
---
 fs/ceph/addr.c      |    8 +-------
 mm/page-writeback.c |    1 +
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 5598a0d..420d469 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -105,13 +105,7 @@ static int ceph_set_page_dirty(struct page *page)
 	spin_lock_irq(&mapping->tree_lock);
 	if (page->mapping) {	/* Race with truncate? */
 		WARN_ON_ONCE(!PageUptodate(page));
-
-		if (mapping_cap_account_dirty(mapping)) {
-			__inc_zone_page_state(page, NR_FILE_DIRTY);
-			__inc_bdi_stat(mapping->backing_dev_info,
-					BDI_RECLAIMABLE);
-			task_io_account_write(PAGE_CACHE_SIZE);
-		}
+		account_page_dirtied(page, page->mapping);
 		radix_tree_tag_set(&mapping->page_tree,
 				page_index(page), PAGECACHE_TAG_DIRTY);
 
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 7262aac..9d07a8d 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1131,6 +1131,7 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
 		task_io_account_write(PAGE_CACHE_SIZE);
 	}
 }
+EXPORT_SYMBOL(account_page_dirtied);
 
 /*
  * For address_spaces which do not use buffers.  Just tag the page as dirty in
-- 
1.7.1

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[PATCH 2/5] mm: account_page_writeback added

[Michael Rubin]

This allows code outside of the mm core to safely manipulate page
writeback state and not worry about the other accounting. Not using
these routines means that some code will lose track of the accounting
and we get bugs.

Modified nilfs2 to use interface.

Signed-off-by: Michael Rubin <mrubin@google.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
 fs/nilfs2/segment.c |    2 +-
 include/linux/mm.h  |    1 +
 mm/page-writeback.c |   13 ++++++++++++-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 9fd051a..5617f16 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1599,7 +1599,7 @@ nilfs_copy_replace_page_buffers(struct page *page, struct list_head *out)
 	kunmap_atomic(kaddr, KM_USER0);
 
 	if (!TestSetPageWriteback(clone_page))
-		inc_zone_page_state(clone_page, NR_WRITEBACK);
+		account_page_writeback(clone_page);
 	unlock_page(clone_page);
 
 	return 0;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 709f672..4b2f38b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -856,6 +856,7 @@ int __set_page_dirty_no_writeback(struct page *page);
 int redirty_page_for_writepage(struct writeback_control *wbc,
 				struct page *page);
 void account_page_dirtied(struct page *page, struct address_space *mapping);
+void account_page_writeback(struct page *page);
 int set_page_dirty(struct page *page);
 int set_page_dirty_lock(struct page *page);
 int clear_page_dirty_for_io(struct page *page);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 9d07a8d..ae5f5d5 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1134,6 +1134,17 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
 EXPORT_SYMBOL(account_page_dirtied);
 
 /*
+ * Helper function for set_page_writeback family.
+ * NOTE: Unlike account_page_dirtied this does not rely on being atomic
+ * wrt interrupts.
+ */
+void account_page_writeback(struct page *page)
+{
+	inc_zone_page_state(page, NR_WRITEBACK);
+}
+EXPORT_SYMBOL(account_page_writeback);
+
+/*
  * For address_spaces which do not use buffers.  Just tag the page as dirty in
  * its radix tree.
  *
@@ -1371,7 +1382,7 @@ int test_set_page_writeback(struct page *page)
 		ret = TestSetPageWriteback(page);
 	}
 	if (!ret)
-		inc_zone_page_state(page, NR_WRITEBACK);
+		account_page_writeback(page);
 	return ret;
 
 }
-- 
1.7.1

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Re: [PATCH 2/5] mm: account_page_writeback added

[Wu Fengguang]

On Mon, Sep 13, 2010 at 04:30:37AM +0800, Michael Rubin wrote:
> This allows code outside of the mm core to safely manipulate page
> writeback state and not worry about the other accounting. Not using
> these routines means that some code will lose track of the accounting
> and we get bugs.
> 
> Modified nilfs2 to use interface.
> 
> Signed-off-by: Michael Rubin <mrubin@google.com>
> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>

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[PATCH 3/5] writeback: nr_dirtied and nr_written in /proc/vmstat

[Michael Rubin]

To help developers and applications gain visibility into writeback
behaviour adding two entries to vm_stat_items and /proc/vmstat. This
will allow us to track the "written" and "dirtied" counts.

   # grep nr_dirtied /proc/vmstat
   nr_dirtied 3747
   # grep nr_written /proc/vmstat
   nr_cleaned 3618

Signed-off-by: Michael Rubin <mrubin@google.com>
---
 include/linux/mmzone.h |    2 ++
 mm/page-writeback.c    |    2 ++
 mm/vmstat.c            |    3 +++
 3 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 6e6e626..d0d7454 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -104,6 +104,8 @@ enum zone_stat_item {
 	NR_ISOLATED_ANON,	/* Temporary isolated pages from anon lru */
 	NR_ISOLATED_FILE,	/* Temporary isolated pages from file lru */
 	NR_SHMEM,		/* shmem pages (included tmpfs/GEM pages) */
+	NR_FILE_DIRTIED,	/* accumulated dirty pages */
+	NR_WRITTEN,		/* accumulated written pages */
 #ifdef CONFIG_NUMA
 	NUMA_HIT,		/* allocated in intended node */
 	NUMA_MISS,		/* allocated in non intended node */
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index ae5f5d5..4d6ef9c 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1126,6 +1126,7 @@ 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_DIRTIED);
 		__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
 		task_dirty_inc(current);
 		task_io_account_write(PAGE_CACHE_SIZE);
@@ -1141,6 +1142,7 @@ EXPORT_SYMBOL(account_page_dirtied);
 void account_page_writeback(struct page *page)
 {
 	inc_zone_page_state(page, NR_WRITEBACK);
+	inc_zone_page_state(page, NR_WRITTEN);
 }
 EXPORT_SYMBOL(account_page_writeback);
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index f389168..d448ef4 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -732,6 +732,9 @@ static const char * const vmstat_text[] = {
 	"nr_isolated_anon",
 	"nr_isolated_file",
 	"nr_shmem",
+	"nr_dirtied",
+	"nr_written",
+
 #ifdef CONFIG_NUMA
 	"numa_hit",
 	"numa_miss",
-- 
1.7.1

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Re: [PATCH 3/5] writeback: nr_dirtied and nr_written in /proc/vmstat

[Wu Fengguang]

On Mon, Sep 13, 2010 at 04:30:38AM +0800, Michael Rubin wrote:
> To help developers and applications gain visibility into writeback
> behaviour adding two entries to vm_stat_items and /proc/vmstat. This
> will allow us to track the "written" and "dirtied" counts.
> 
>    # grep nr_dirtied /proc/vmstat
>    nr_dirtied 3747
>    # grep nr_written /proc/vmstat
>    nr_cleaned 3618

s/nr_cleaned/nr_written

Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>

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[PATCH 4/5] writeback: Adding /sys/devices/system/node/<node>/vmstat

[Michael Rubin]

For NUMA node systems it is important to have visibility in memory
characteristics. Two of the /proc/vmstat values "nr_cleaned" and
"nr_dirtied" are added here.

	# cat /sys/devices/system/node/node20/vmstat
	nr_cleaned 0
	nr_dirtied 0

Signed-off-by: Michael Rubin <mrubin@google.com>
---
 drivers/base/node.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 2872e86..6aaccd9 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_vmstat(struct sys_device *dev,
+				struct sysdev_attribute *attr, char *buf)
+{
+	int nid = dev->id;
+	return sprintf(buf,
+		"nr_written %lu\n"
+		"nr_dirtied %lu\n",
+		node_page_state(nid, NR_WRITTEN),
+		node_page_state(nid, NR_FILE_DIRTIED));
+}
+static SYSDEV_ATTR(vmstat, S_IRUGO, node_read_vmstat, 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_vmstat);
 
 		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_vmstat);
 
 	scan_unevictable_unregister_node(node);
 	hugetlb_unregister_node(node);		/* no-op, if memoryless node */
-- 
1.7.1

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Re: [PATCH 4/5] writeback: Adding /sys/devices/system/node/<node>/vmstat

[Wu Fengguang]

On Mon, Sep 13, 2010 at 04:30:39AM +0800, Michael Rubin wrote:
> For NUMA node systems it is important to have visibility in memory
> characteristics. Two of the /proc/vmstat values "nr_cleaned" and

s/nr_cleaned/nr_written/

> "nr_dirtied" are added here.
> 
> 	# cat /sys/devices/system/node/node20/vmstat
> 	nr_cleaned 0

ditto

> 	nr_dirtied 0
> 
> Signed-off-by: Michael Rubin <mrubin@google.com>

Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>

> +static ssize_t node_read_vmstat(struct sys_device *dev,
> +				struct sysdev_attribute *attr, char *buf)
> +{
> +	int nid = dev->id;
> +	return sprintf(buf,
> +		"nr_written %lu\n"
> +		"nr_dirtied %lu\n",
> +		node_page_state(nid, NR_WRITTEN),
> +		node_page_state(nid, NR_FILE_DIRTIED));
> +}

Do you have plan to port more vmstat_text[] items? :)

Thanks,
Fengguang

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Re: [PATCH 4/5] writeback: Adding /sys/devices/system/node/<node>/vmstat

[Michael Rubin]

On Sun, Sep 12, 2010 at 8:02 PM, Wu Fengguang <fengguang.wu@intel.com> wrote:
> Do you have plan to port more vmstat_text[] items? :)

Yes. I feel bound to do it after all your help. :-)
I may need a few weeks to resolve some other issues but I can get back to this.

mrubin

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[PATCH 5/5] writeback: Reporting dirty thresholds in /proc/vmstat

[Michael Rubin]

The kernel already exposes the user desired thresholds in /proc/sys/vm
with dirty_background_ratio and background_ratio. But the kernel may
alter the number requested without giving the user any indication that
is the case.

Knowing the actual ratios the kernel is honoring can help app developers
understand how their buffered IO will be sent to the disk.

        $ grep threshold /proc/vmstat
        nr_dirty_threshold 409111
        nr_dirty_background_threshold 818223

Signed-off-by: Michael Rubin <mrubin@google.com>
---
 include/linux/mmzone.h |    2 ++
 mm/vmstat.c            |    4 ++++
 2 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index d0d7454..1e87936 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -106,6 +106,8 @@ enum zone_stat_item {
 	NR_SHMEM,		/* shmem pages (included tmpfs/GEM pages) */
 	NR_FILE_DIRTIED,	/* accumulated dirty pages */
 	NR_WRITTEN,		/* accumulated written pages */
+	NR_DIRTY_THRESHOLD,	/* writeback threshold */
+	NR_DIRTY_BG_THRESHOLD,	/* bg writeback threshold */
 #ifdef CONFIG_NUMA
 	NUMA_HIT,		/* allocated in intended node */
 	NUMA_MISS,		/* allocated in non intended node */
diff --git a/mm/vmstat.c b/mm/vmstat.c
index d448ef4..0c1ddca 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -17,6 +17,7 @@
 #include <linux/vmstat.h>
 #include <linux/sched.h>
 #include <linux/math64.h>
+#include <linux/writeback.h>
 
 #ifdef CONFIG_VM_EVENT_COUNTERS
 DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
@@ -734,6 +735,8 @@ static const char * const vmstat_text[] = {
 	"nr_shmem",
 	"nr_dirtied",
 	"nr_written",
+	"nr_dirty_threshold",
+	"nr_dirty_background_threshold",
 
 #ifdef CONFIG_NUMA
 	"numa_hit",
@@ -917,6 +920,7 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
 		return ERR_PTR(-ENOMEM);
 	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
 		v[i] = global_page_state(i);
+	global_dirty_limits(v + NR_DIRTY_BG_THRESHOLD, v + NR_DIRTY_THRESHOLD);
 #ifdef CONFIG_VM_EVENT_COUNTERS
 	e = v + NR_VM_ZONE_STAT_ITEMS;
 	all_vm_events(e);
-- 
1.7.1

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Re: [PATCH 5/5] writeback: Reporting dirty thresholds in /proc/vmstat

[Wu Fengguang]

On Mon, Sep 13, 2010 at 04:30:40AM +0800, Michael Rubin wrote:
> The kernel already exposes the user desired thresholds in /proc/sys/vm
> with dirty_background_ratio and background_ratio. But the kernel may
> alter the number requested without giving the user any indication that
> is the case.
> 
> Knowing the actual ratios the kernel is honoring can help app developers
> understand how their buffered IO will be sent to the disk.
> 
>         $ grep threshold /proc/vmstat
>         nr_dirty_threshold 409111
>         nr_dirty_background_threshold 818223
> 
> Signed-off-by: Michael Rubin <mrubin@google.com>
> ---
>  include/linux/mmzone.h |    2 ++
>  mm/vmstat.c            |    4 ++++
>  2 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index d0d7454..1e87936 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -106,6 +106,8 @@ enum zone_stat_item {
>  	NR_SHMEM,		/* shmem pages (included tmpfs/GEM pages) */
>  	NR_FILE_DIRTIED,	/* accumulated dirty pages */
>  	NR_WRITTEN,		/* accumulated written pages */
> +	NR_DIRTY_THRESHOLD,	/* writeback threshold */

s/writeback/dirty throttling/

> +	NR_DIRTY_BG_THRESHOLD,	/* bg writeback threshold */

I have no idea about this interface change. No ACK or NAK.

But technical wise, the above two enum items should better be removed
to avoid possibly eating one more cache line. The two items can be
printed by explicit code.

Thanks,
Fengguang

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Re: [PATCH 5/5] writeback: Reporting dirty thresholds in /proc/vmstat

[Michael Rubin]

On Sun, Sep 12, 2010 at 8:15 PM, Wu Fengguang <fengguang.wu@intel.com> wrote:

> But technical wise, the above two enum items should better be removed
> to avoid possibly eating one more cache line. The two items can be
> printed by explicit code.

Done. Patch coming.

mrubin

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[PATCH 0/5] writeback: kernel visibility

[Michael Rubin]

Patch #1 sets up some helper functions for account_page_dirty and fixes
a bug in ceph

Patch #2 sets up some helper functions for account_page_writeback

Patch #3 adds writeback visibility in /proc/vmstat

To help developers and applications gain visibility into writeback
behaviour this patch adds two counters to /proc/vmstat.

  # grep nr_dirtied /proc/vmstat
  nr_dirtied 3747
  # grep nr_written /proc/vmstat
  nr_written 3618

These entries allow user apps to understand writeback behaviour over
time and learn how it is impacting their performance. Currently there
is no way to inspect dirty and writeback speed over time. It's not
possible for nr_dirty/nr_writeback.

These entries are necessary to give visibility into writeback
behaviour. We have /proc/diskstats which lets us understand the io in
the block layer. We have blktrace for more in depth understanding. We have
e2fsprogs and debugsfs to give insight into the file systems behaviour,
but we don't offer our users the ability understand what writeback is
doing. There is no way to know how active it is over the whole system,
if it's falling behind or to quantify it's efforts. With these values
exported users can easily see how much data applications are sending
through writeback and also at what rates writeback is processing this
data. Comparing the rates of change between the two allow developers
to see when writeback is not able to keep up with incoming traffic and
the rate of dirty memory being sent to the IO back end. This allows
folks to understand their io workloads and track kernel issues. Non
kernel engineers at Google often use these counters to solve puzzling
performance problems.

Patch #4 adds a pernode vmstat file with nr_dirtied and nr_written

Patch #5 add writeback thresholds to /proc/vmstat

Currently these values are in debugfs. But they should be promoted to
/proc since they are useful for developers who are writing databases
and file servers and are not debugging the kernel.

The output is as below:

 # grep threshold /proc/vmstat
 nr_pages_dirty_threshold 409111
 nr_pages_dirty_background_threshold 818223

Michael Rubin (5):
  mm: exporting account_page_dirty
  mm: account_page_writeback added
  writeback: nr_dirtied and nr_written in /proc/vmstat
  writeback: Adding /sys/devices/system/node/<node>/vmstat
  writeback: Reporting dirty thresholds in /proc/vmstat

 drivers/base/node.c    |   14 ++++++++++++++
 fs/ceph/addr.c         |    8 +-------
 fs/nilfs2/segment.c    |    2 +-
 include/linux/mm.h     |    1 +
 include/linux/mmzone.h |    2 ++
 mm/page-writeback.c    |   16 +++++++++++++++-
 mm/vmstat.c            |   42 ++++++++++++++++++++++++++++--------------
 7 files changed, 62 insertions(+), 23 deletions(-)

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[PATCH 2/5] mm: account_page_writeback added

[Michael Rubin]

This allows code outside of the mm core to safely manipulate page
writeback state and not worry about the other accounting. Not using
these routines means that some code will lose track of the accounting
and we get bugs.

Modified nilfs2 to use interface.

Signed-off-by: Michael Rubin <mrubin@google.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
---
 fs/nilfs2/segment.c |    2 +-
 include/linux/mm.h  |    1 +
 mm/page-writeback.c |   13 ++++++++++++-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 9fd051a..5617f16 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1599,7 +1599,7 @@ nilfs_copy_replace_page_buffers(struct page *page, struct list_head *out)
 	kunmap_atomic(kaddr, KM_USER0);
 
 	if (!TestSetPageWriteback(clone_page))
-		inc_zone_page_state(clone_page, NR_WRITEBACK);
+		account_page_writeback(clone_page);
 	unlock_page(clone_page);
 
 	return 0;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 709f672..4b2f38b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -856,6 +856,7 @@ int __set_page_dirty_no_writeback(struct page *page);
 int redirty_page_for_writepage(struct writeback_control *wbc,
 				struct page *page);
 void account_page_dirtied(struct page *page, struct address_space *mapping);
+void account_page_writeback(struct page *page);
 int set_page_dirty(struct page *page);
 int set_page_dirty_lock(struct page *page);
 int clear_page_dirty_for_io(struct page *page);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 9d07a8d..ae5f5d5 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1134,6 +1134,17 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
 EXPORT_SYMBOL(account_page_dirtied);
 
 /*
+ * Helper function for set_page_writeback family.
+ * NOTE: Unlike account_page_dirtied this does not rely on being atomic
+ * wrt interrupts.
+ */
+void account_page_writeback(struct page *page)
+{
+	inc_zone_page_state(page, NR_WRITEBACK);
+}
+EXPORT_SYMBOL(account_page_writeback);
+
+/*
  * For address_spaces which do not use buffers.  Just tag the page as dirty in
  * its radix tree.
  *
@@ -1371,7 +1382,7 @@ int test_set_page_writeback(struct page *page)
 		ret = TestSetPageWriteback(page);
 	}
 	if (!ret)
-		inc_zone_page_state(page, NR_WRITEBACK);
+		account_page_writeback(page);
 	return ret;
 
 }
-- 
1.7.1

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