doc: clarify the behaviour of dirty_ratio/dirty_bytes
Subsystems (2)
PATCH 1/1 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 <[email protected]>
Acked-by David Rientjes <[email protected]>
Signed-off-by Andrea Righi <[email protected]>
--- Documentation/sysctl/vm.txt | 12 ++++++++---- 1 files changed, 8 insertions(+), 4 deletions(-)
Documentation/sysctl/vm.txt +8 -4
@@ -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
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