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SubjectRe: [RFC PATCH 0/3] Avoid the use of congestion_wait under zone pressure
On Mon,  8 Mar 2010 11:48:20 +0000
Mel Gorman <mel@csn.ul.ie> wrote:

> Under memory pressure, the page allocator and kswapd can go to sleep using
> congestion_wait(). In two of these cases, it may not be the appropriate
> action as congestion may not be the problem.

clear_bdi_congested() is called each time a write completes and the
queue is below the congestion threshold.

So if the page allocator or kswapd call congestion_wait() against a
non-congested queue, they'll wake up on the very next write completion.

Hence the above-quoted claim seems to me to be a significant mis-analysis and
perhaps explains why the patchset didn't seem to help anything?


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