Hi Mel,



2016-06-03 14:36 GMT+02:00 Mel Gorman [off-list ref]:

On Fri, Jun 03, 2016 at 01:57:06PM +0200, Marcin Wojtas wrote:

quoted

quoted

quoted

For the record: the newest kernel I was able to reproduce the dumps
was v4.6: http://pastebin.com/ekDdACn5. I've just checked v4.7-rc1,
which comprise a lot (mainly yours) changes in mm, and I'm wondering
if there may be a spot fix or rather a series of improvements. I'm
looking forward to your opinion and would be grateful for any advice.

I don't believe we want to reintroduce the reserve to cope with CMA. One
option would be to widen the gap between low and min watermark by the
size of the CMA region. The effect would be to wake kswapd earlier which
matters considering the context of the failing allocation was
GFP_ATOMIC.

Of course my intention is not reintroducing anything that's gone
forever, but just to find out way to overcome current issues. Do you
mean increasing CMA size?

No. There is a gap between the low and min watermarks. At the low point,
kswapd is woken up and at the min point allocation requests either
either direct reclaim or fail if they are atomic. What I'm suggesting
is that you adjust the low watermark and add the size of the CMA area
to it so that kswapd is woken earlier. The watermarks are calculated in
__setup_per_zone_wmarks

I printed all zones' settings, whose watermarks are configured within
__setup_per_zone_wmarks(). There are three DMA, Normal and Movable -
only first one's watermarks have non-zero values. Increasing DMA min
watermark didn't help. I also played with increasing
/proc/sys/vm/min_free_kbytes from ~2560 to 16000
(__setup_per_zone_wmarks() recalculates watermarks after that) - no
effect either.

Best regards,
Marcin

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