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authorAndrea Righi <arighi@develer.com>2010-10-27 15:33:31 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-10-27 18:03:08 -0700
commitabffc0207f12563f17bbde96e4cc0d9f3d7e2a53 (patch)
tree42a2b7ea028cf0bdc2b5f2d38386507768c8fe5c /Documentation/sysctl/vm.txt
parente45c9effed903ba3fdbd6ef0498ee8989c35af0a (diff)
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doc: clarify the behaviour of dirty_ratio/dirty_bytes
When dirty_ratio or dirty_bytes is written the other parameter is disabled and set to 0 (in dirty_bytes_handler() / dirty_ratio_handler()). We do the same for dirty_background_ratio and dirty_background_bytes. However, in the sysctl documentation, we say that the counterpart becomes a function of the old value, that is not correct. Clarify the documentation reporting the actual behaviour. Reviewed-by: Greg Thelen <gthelen@google.com> Acked-by: David Rientjes <rientjes@google.com> Signed-off-by: Andrea Righi <arighi@develer.com> Cc: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/sysctl/vm.txt')
-rw-r--r--Documentation/sysctl/vm.txt12
1 files changed, 8 insertions, 4 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index b606c2c4dd37..30289fab86eb 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -80,8 +80,10 @@ dirty_background_bytes
Contains the amount of dirty memory at which the pdflush background writeback
daemon will start writeback.
-If dirty_background_bytes is written, dirty_background_ratio becomes a function
-of its value (dirty_background_bytes / the amount of dirtyable system memory).
+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
+immediately taken into account to evaluate the dirty memory limits and the
+other appears as 0 when read.
==============================================================
@@ -97,8 +99,10 @@ dirty_bytes
Contains the amount of dirty memory at which a process generating disk writes
will itself start writeback.
-If dirty_bytes is written, dirty_ratio becomes a function of its value
-(dirty_bytes / the amount of dirtyable system memory).
+Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be
+specified at a time. When one sysctl is written it is immediately taken into
+account to evaluate the dirty memory limits and the other appears as 0 when
+read.
Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
value lower than this limit will be ignored and the old configuration will be