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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>
This commit is contained in:
Andrea Righi 2010-10-27 15:33:31 -07:00 committed by Linus Torvalds
parent e45c9effed
commit abffc0207f
1 changed files with 8 additions and 4 deletions
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12
Documentation/sysctl/vm.txt
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@ -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