Re: [PATCH] bdi flusher should not be throttled here when it fall into buddy slow path

[Mel Gorman]

On Tue, Oct 18, 2016 at 03:12:45PM +0800, zhouxianrong@xxxxxxxxxx wrote:
> From: z00281421 <z00281421@xxxxxxxxxxxxxxxxxxxx>
> 
> bdi flusher may enter page alloc slow path due to writepage and kmalloc. 
> in that case the flusher as a direct reclaimer should not be throttled here
> because it can not to reclaim clean file pages or anaonymous pages
> for next moment; furthermore writeback rate of dirty pages would be
> slow down and other direct reclaimers and kswapd would be affected.
> bdi flusher should be iosceduled by get_request rather than here.
> 
> Signed-off-by: z00281421 <z00281421@xxxxxxxxxxxxxxxxxxxx>

What does this patch do that PF_LESS_THROTTLE is not doing already if
there is an underlying BDI?

There have been a few patches like this recently that look like they might
do something useful but are subtle. They really should be accompanied by
a test case and data showing they either fix a functional issue (machine
livelocking due to writeback not making progress) or a performance issue.

-- 
Mel Gorman
SUSE Labs