Re: [patch 1/2] mm: page-writeback: fix dirty_balance_reserve subtractionfrom dirtyable memory

[Rik van Riel]

On 01/24/2014 05:03 PM, Johannes Weiner wrote:
> The dirty_balance_reserve is an approximation of the fraction of free
> pages that the page allocator does not make available for page cache
> allocations.  As a result, it has to be taken into account when
> calculating the amount of "dirtyable memory", the baseline to which
> dirty_background_ratio and dirty_ratio are applied.
> 
> However, currently the reserve is subtracted from the sum of free and
> reclaimable pages, which is non-sensical and leads to erroneous
> results when the system is dominated by unreclaimable pages and the
> dirty_balance_reserve is bigger than free+reclaimable.  In that case,
> at least the already allocated cache should be considered dirtyable.
> 
> Fix the calculation by subtracting the reserve from the amount of free
> pages, then adding the reclaimable pages on top.
> 
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>

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