Date:	Wed, 25 Jul 2012 18:12:01 +0300
From:	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linux Kernel Maling List <linux-kernel@...r.kernel.org>,
	Linux FS Maling List <linux-fsdevel@...r.kernel.org>,
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
	Randy Dunlap <rdunlap@...otime.net>
Subject: [PATCH 03/16] Documentation: fix the VM knobs descritpion WRT pdflush

From: Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>

The pdflush thread is long gone, however we still mention it incorrectly in the
kernel documentation. This patch fixes the situation.

Cc: Randy Dunlap <rdunlap@...otime.net>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
---

I expect this patch to be merged via Al Viro's VFS tree.

 Documentation/laptops/laptop-mode.txt |   12 ++++++------
 Documentation/sysctl/vm.txt           |   25 ++++++++++++++-----------
 2 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/Documentation/laptops/laptop-mode.txt b/Documentation/laptops/laptop-mode.txt
index 0bf25ee..4ebbfc3 100644
--- a/Documentation/laptops/laptop-mode.txt
+++ b/Documentation/laptops/laptop-mode.txt
@@ -262,9 +262,9 @@ MINIMUM_BATTERY_MINUTES=10
 
 #
 # Allowed dirty background ratio, in percent.  Once DIRTY_RATIO has been
-# exceeded, the kernel will wake pdflush which will then reduce the amount
-# of dirty memory to dirty_background_ratio.  Set this nice and low, so once
-# some writeout has commenced, we do a lot of it.
+# exceeded, the kernel will wake flusher threads which will then reduce the
+# amount of dirty memory to dirty_background_ratio.  Set this nice and low,
+# so once some writeout has commenced, we do a lot of it.
 #
 #DIRTY_BACKGROUND_RATIO=5
 
@@ -384,9 +384,9 @@ CPU_MAXFREQ=${CPU_MAXFREQ:-'slowest'}
 
 #
 # Allowed dirty background ratio, in percent.  Once DIRTY_RATIO has been
-# exceeded, the kernel will wake pdflush which will then reduce the amount
-# of dirty memory to dirty_background_ratio.  Set this nice and low, so once
-# some writeout has commenced, we do a lot of it.
+# exceeded, the kernel will wake flusher threads which will then reduce the
+# amount of dirty memory to dirty_background_ratio.  Set this nice and low,
+# so once some writeout has commenced, we do a lot of it.
 #
 DIRTY_BACKGROUND_RATIO=${DIRTY_BACKGROUND_RATIO:-'5'}
 
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 96f0ee8..cec12bb 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -77,8 +77,8 @@ huge pages although processes will also directly compact memory as required.
 
 dirty_background_bytes
 
-Contains the amount of dirty memory at which the pdflush background writeback
-daemon will start writeback.
+Contains the amount of dirty memory at which the background kernel
+flusher threads will start writeback.
 
 Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only
 one of them may be specified at a time. When one sysctl is written it is
@@ -90,7 +90,7 @@ other appears as 0 when read.
 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.
+the background kernel flusher threads will start writing out dirty data.
 
 ==============================================================
 
@@ -113,9 +113,9 @@ retained.
 dirty_expire_centisecs
 
 This tunable is used to define when dirty data is old enough to be eligible
-for writeout by the pdflush daemons.  It is expressed in 100'ths of a second.
-Data which has been dirty in-memory for longer than this interval will be
-written out next time a pdflush daemon wakes up.
+for writeout by the kernel flusher threads.  It is expressed in 100'ths
+of a second.  Data which has been dirty in-memory for longer than this
+interval will be written out next time a flusher thread wakes up.
 
 ==============================================================
 
@@ -129,7 +129,7 @@ data.
 
 dirty_writeback_centisecs
 
-The pdflush writeback daemons will periodically wake up and write `old' data
+The kernel flusher threads will periodically wake up and write `old' data
 out to disk.  This tunable expresses the interval between those wakeups, in
 100'ths of a second.
 
@@ -428,11 +428,14 @@ 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.
+This is not used by the kernel since version 2.6.32, this is read-only
+and is always set to 1.  Preserve for backward-compatibility reasons.
 
-When necessary, additional pdflush threads are created, one per second, up to
-nr_pdflush_threads_max.
+In the past, it contained the current number of pdflush threads.  The
+value changed according to the number of dirty pages in the system.
+When necessary, additional pdflush threads were created, one per second.
+However, in kernel version 2.6.32 the pdflush thread was removed in
+favour of per-block device bdi flusher threads.
 
 ==============================================================
 
-- 
1.7.10

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