Re: [PATCH][5/?] count writeback pages in nr_scanned

[Andrew Morton]

Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote:
>
> > 
> > I suspect something might still be broken.  It may take a few
> > days of continuous testing to trigger the bug, though ...
> > 
> 
> It is possible to be those blk_congestion_wait paths, because
> the queue simply won't be congested. So doing io_schedule_timeout
> might help.

If the queue is not congested, blk_congestion_wait() will still sleep.  See
freed_request().

> I wonder if reducing the size of the write queue in CFQ would help
> too? IIRC, it only really wants a huge read queue.

Surely it will help - but we need to be able to handle the situation
because memory can still become full of PageWriteback pages if there are
many disks.
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