Hi Mel, My last email got cut in half. 2016-06-08 12:09 GMT+02:00 Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>: > On Tue, Jun 07, 2016 at 07:36:57PM +0200, Marcin Wojtas wrote: >> Hi Mel, >> >> >> >> 2016-06-03 14:36 GMT+02:00 Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>: >> > On Fri, Jun 03, 2016 at 01:57:06PM +0200, Marcin Wojtas wrote: >> >> >> 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 > > Patch? > I played with increasing min_free_kbytes from ~2600 to 16000. It resulted in shifting watermarks levels in __setup_per_zone_wmarks(), however only for zone DMA. Normal and Movable remained at 0. No progress with avoiding page alloc failures - a gap between 'free' and 'free_cma' was huge, so I don't think that CMA itself would be a root cause. > Did you establish why GFP_ATOMIC (assuming that's the failing site) had > not specified __GFP_ATOMIC at the time of the allocation failure? > Yes. It happens in new_slab() in following lines: return allocate_slab(s, flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK), node); I added "| GFP_ATOMIC" and in such case I got same dumps but with one bit set more in gfp_mask, so I don't think it's an issue. Latest patches in v4.7-rc1 seem to boost page alloc performance enough to avoid problems observed between v4.2 and v4.6. Hence before rebasing from v4.4 to another LTS >v4.7 in future, we decided as a WA to return to using MIGRATE_RESERVE + adding fix for early_page_nid_uninitialised(). Now operation seems stable on all our SoC's during the tests. Best regards, Marcin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>