User mode stalls - can it be...?

[Roger Larsson <roger.larsson@norran.net>]

Hi,


I have an idea why we get the stalls!

If we end up in a situation where our write attempts are rejected
due to lack of resources - we will continue happily with next and
next...

Count hits zero and we return

But kswapd finds out that there is more to do and calls another
shrink_mmap...
(and need_resched is not set due to lower priority)

Gives, busy wait in shrink_mmap until pages are written...

I tried to renice 15 kswapd with improved results (I am using my patched
kernels)
Another approach would be to always sleep...

/RogerL

(Sent privately to Quintela and Riel - but it might be of value for
 someone else too...)

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